Invertebrate Welfare Cause Profile

Ex­ec­u­tive Summary

More than 99.9% of an­i­mals are in­ver­te­brates. There is mod­est ev­i­dence that some large groups of in­ver­te­brates, es­pe­cially cephalopods and arthro­pods, are sen­tient. The effec­tive an­i­mal ac­tivism com­mu­nity cur­rently al­lo­cates less than 1% of to­tal spend­ing to in­ver­te­brate welfare. That share should rise so that we can bet­ter un­der­stand in­ver­te­brate sen­tience and in­ves­ti­gate the tractabil­ity of im­prov­ing in­ver­te­brate welfare.

In­tro­duc­tion and Context

This post is the tenth in Re­think Pri­ori­ties’ se­ries on in­ver­te­brate welfare. In the first post we ex­am­ine some philo­soph­i­cal difficul­ties in­her­ent in the de­tec­tion of morally sig­nifi­cant pain and plea­sure in non­hu­mans. In the sec­ond post we dis­cuss our sur­vey and com­pila­tion of the ex­tant sci­en­tific liter­a­ture rele­vant to in­ver­te­brate sen­tience, as well as the strengths and weak­nesses of our ap­proach to the sub­ject. In the third post we ex­plain some anatom­i­cal, evolu­tion­ary, and be­hav­ioral fea­tures po­ten­tially in­dica­tive of the ca­pac­ity for con­scious ex­pe­rience in in­ver­te­brates. In the fourth post we ex­plain some drug re­sponses, mo­ti­va­tional trade­offs, and feats of cog­ni­tive so­phis­ti­ca­tion po­ten­tially in­dica­tive of the ca­pac­ity for con­scious ex­pe­rience in in­ver­te­brates. In the fifth post we ex­plain some learn­ing in­di­ca­tors, nav­i­ga­tional skills, and mood state be­hav­iors po­ten­tially in­dica­tive of the ca­pac­ity for con­scious ex­pe­rience in in­ver­te­brates. The sixth post an­nounces our In­ver­te­brate Sen­tience Table. In the sev­enth and eighth posts, we pre­sent our sum­mary of find­ings by fea­ture and by taxa. The ninth post asks what we can learn about sen­tience from ex­am­in­ing pro­cess that op­er­ate un­con­sciously in hu­mans.

In this post we ap­ply the stan­dard im­por­tance-ne­glect­ed­ness-tractabil­ity frame­work to in­ver­te­brate welfare to de­ter­mine, as best we can, whether this is a cause area that is worth pri­ori­tiz­ing. We con­clude that it is. In a sep­a­rate post, slated to be pub­lished next month, we pre­sent and ex­am­ine the best ar­gu­ments against our anal­y­sis.

What Is In­ver­te­brate Welfare?

In­ver­te­brates[1] com­prise an enor­mous and di­verse ar­ray of an­i­mals, from ne­ma­todes and earth­worms to jump­ing spi­ders and jel­lyfish, crabs and krill to cut­tlefish and cock­roaches. Be­cause in­ver­te­brates are a large and het­ero­ge­neous class of an­i­mals, there are few things that can be said about in­ver­te­brates in gen­eral (other than that they are an­i­mals that lack a back­bone). More­over, it is un­cer­tain which (if any) in­ver­te­brates have the ca­pac­ity for valenced ex­pe­rience,[2] so it is un­clear whether these an­i­mals have a welfare. Thus, the term ‘in­ver­te­brate welfare’ is in­evitably mis­lead­ing.[3] Us­ing the term to de­note a cause area is some­thing of a ter­minolog­i­cal sim­plifi­ca­tion.

If in­ver­te­brate welfare were a ma­ture field, it would en­com­pass per­haps dozens of dis­tinct and un­re­lated in­ter­ven­tions.[4] A cam­paign to pro­mote the use of hu­mane in­sec­ti­cides is quite differ­ent in kind from a cam­paign to pro­mote strict lab­o­ra­tory stan­dards for the treat­ment of oc­to­puses.[5] What the in­ter­ven­tions have in com­mon is that they con­cern a group of an­i­mals whose welfare has his­tor­i­cally been ig­nored.

When we con­sider the ar­gu­ments for and against pri­ori­tiz­ing in­ver­te­brate welfare as a cause area, what we are con­sid­er­ing is whether we should pri­ori­tize learn­ing more about this group of an­i­mals. At this early stage, sup­port­ing the cause of in­ver­te­brate welfare means sup­port­ing ad­di­tional re­search on in­ver­te­brate sen­tience, ad­vo­cacy strate­gies, and cost-effec­tive in­ter­ven­tions. Op­pos­ing the cause means de-pri­ori­tiz­ing this re­search. It’s pos­si­ble to sup­port the cause now, and, as the re­sults of the ad­di­tional re­search come in, later op­pose the cause.

Com­pli­cat­ing mat­ters fur­ther, the moral sta­tus of in­ver­te­brates is al­most cer­tainly not uniform across the cat­e­gory. Sup­port­ing in­ver­te­brate welfare as a cause area does not mean cham­pi­oning all in­ver­te­brates equally. Car­ing about highly in­tel­li­gent cephalopods doesn’t en­tail car­ing about brain­less cnidar­i­ans. Part of the in­ver­te­brate welfare pro­ject is de­ter­min­ing which in­ver­te­brates (if any) mat­ter and to what de­gree.

Scale and Limit­ing Factors

The (Rough) Num­ber of Invertebrates

First, a caveat: es­ti­mat­ing the num­ber of in­ver­te­brates is hard. Most in­ver­te­brates are small, wild, short-lived, ge­o­graph­i­cally dis­persed, and, as a re­sult, difficult to sys­tem­at­i­cally col­lect and count. More­over, there are few aca­demic or eco­nomic mo­ti­va­tions to un­der­take the ar­du­ous task of es­ti­mat­ing global pop­u­la­tion sizes for most in­ver­te­brates. As a con­se­quence, many of the es­ti­mates pre­sented in this sec­tion could eas­ily be wrong, in ei­ther di­rec­tion, by one or more or­ders of mag­ni­tude. Nonethe­less, one fact is clear: there are many, many more in­ver­te­brates than ver­te­brates.

In­ver­te­brates ac­count for ap­prox­i­mately 85% of all an­i­mal bio­mass. How­ever, be­cause the mass of in­di­vi­d­ual an­i­mals varies by many or­ders of mag­ni­tude across taxa, this figure vastly un­der­states the ex­tent to which in­di­vi­d­ual in­ver­te­brates out­num­ber in­di­vi­d­ual ver­te­brates. More than 98% of all ex­tant an­i­mal species are in­ver­te­brates. Again, though, be­cause the num­ber of an­i­mals per species is not uniform across taxa, this figure also un­der­states the ex­tent to which in­di­vi­d­ual in­ver­te­brates out­num­ber in­di­vi­d­ual ver­te­brates. Re­cent es­ti­mates put the to­tal num­ber of an­i­mals on earth at around a sex­til­lion. Of that sex­til­lion, ap­prox­i­mately 99.9998% are in­ver­te­brates.[6] From the point of view of to­tal in­di­vi­d­u­als, ‘an­i­mals’ is ba­si­cally syn­ony­mous with ‘in­ver­te­brates.’

Of course, from a welfare per­spec­tive, the to­tal num­ber of in­ver­te­brates is ir­rele­vant if only a hand­ful of in­ver­te­brate species are sen­tient. An­nelids and ne­ma­todes are ex­tremely nu­mer­ous,[7] but they are less plau­si­bly moral pa­tients than, for ex­am­ple, coleoid cephalopods (such as oc­to­puses and cut­tlefish), de­ca­pod crus­taceans (such as crabs, lob­sters, and crayfish), and eu­so­cial in­sects (such as ants, bees, and ter­mites). It will be helpful, then, to look at more fine-grained pop­u­la­tion es­ti­mates.

To­tal in­sects num­ber some­where be­tween 1 and 10 quin­til­lion,[8] of which ants are by far the most nu­mer­ous. (Ants alone ac­count for roughly 15% of ter­res­trial an­i­mal bio­mass.) Antarc­tic krill (Euphau­sia su­perba) are the most nu­mer­ous marine arthro­pod (and, by weight, the largest sin­gle an­i­mal species on the planet). Re­cent stud­ies put the to­tal num­ber of Antarc­tic krill at any given mo­ment in time at 800 trillion.[9] (That’s just shy of the to­tal num­ber of in­di­vi­d­ual fish across all fish species.) Fish­count.org es­ti­mates that be­tween 220 billion and 526 billion de­ca­pod crus­taceans were slaugh­tered in aqua­cul­ture pro­duc­tion in 2015 alone.[10] (This figure doesn’t in­clude de­capods that died be­fore slaugh­ter.) Even the lower es­ti­mate is al­most three times the num­ber of land ver­te­brates slaugh­tered for food each year. Based on an anal­y­sis of cephalo­pod prey pop­u­la­tions, it has been es­ti­mated that the to­tal bio­mass of cephalopods is ap­prox­i­mately 0.05 gi­ga­tonnes car­bon.[11] (In­di­vi­d­ual cephalopods range in mass from less than a gram to al­most 200 kilo­grams for the gi­ant squid.) That num­ber com­pares fa­vor­ably to the to­tal bio­mass of hu­mans at 0.06 gi­ga­tonnes car­bon, and far out­strips the bio­mass of wild mam­mals (0.007 Gt C) and wild birds (0.002 Gt C).[12]

Th­ese num­bers alone don’t tell us that in­ver­te­brate welfare is an im­por­tant cause area. Even if most in­ver­te­brates are sen­tient, it might be the case that there is lit­tle we can do to im­prove their welfare, ei­ther due to a lack of cost-effec­tive in­ter­ven­tions or per­haps be­cause in­ver­te­brate lives are already mostly pos­i­tive. We know pre­cious lit­tle about the life his­tory of most in­ver­te­brates and even less about the in­ter­ven­tions that might im­prove those lives. The point of this sec­tion is to show that if there is a non-neg­ligible chance that in­ver­te­brates have the ca­pac­ity for morally sig­nifi­cant valenced ex­pe­rience, then it fol­lows that there is a huge pot of ex­pected moral worth out there that has hith­erto been al­most com­pletely ne­glected. To re­it­er­ate a point above, sup­port­ing in­ver­te­brate welfare at this stage of our un­der­stand­ing merely en­tails sup­port­ing ad­di­tional re­search into this group of an­i­mals.

Mo­ral Weight of Invertebrates

One sub­ject that looms large here and must be ad­dressed di­rectly is the rel­a­tive moral weight of (var­i­ous groups of) in­ver­te­brates. Even if it’s true that there are quin­til­lions of in­ver­te­brates with the ca­pac­ity for valenced ex­pe­rience, if the moral sig­nifi­cance of these ex­pe­riences is neg­ligible, then the to­tal moral value of all in­ver­te­brates may not amount to much.

Ques­tions of moral weight are no­to­ri­ously difficult to ad­ju­di­cate. To sim­plify a bit, we can as­sume that, for a fixed lifes­pan, if crea­ture x has less moral weight than crea­ture y, it’s be­cause x has fewer in­trin­sic morally sig­nifi­cant prop­er­ties and/​or x has those prop­er­ties to a lesser de­gree.[13] Of course, we don’t know what all the morally sig­nifi­cant prop­er­ties are, and even if we did, we prob­a­bly don’t have epistemic ac­cess to all of them. (For ex­am­ple, even if we were cer­tain that gen­eral in­tel­li­gence were the only morally sig­nifi­cant trait, we would still have a hard time de­ter­min­ing rel­a­tive moral weight with much pre­ci­sion be­cause gen­eral in­tel­li­gence is ex­traor­di­nar­ily difficult to mea­sure across dis­similar taxa.) So dis­cus­sions of moral weight in­evitably rely on im­perfect prox­ies and even more im­perfect in­tu­itions.

Sup­pose that the only in­trin­sic morally sig­nifi­cant fea­ture of an en­tity is its phe­nom­e­nally con­scious ex­pe­ri­en­tial states. For crea­tures with the ca­pac­ity for valenced ex­pe­rience, these states can come with a pos­i­tive or nega­tive af­fect. But of course, the dis­tinc­tion is not bi­nary. Some pos­i­tive states are much bet­ter than other pos­i­tive states, and some nega­tive states are much worse than other nega­tive states. Call this the phe­nom­e­nal in­ten­sity of valenced ex­pe­rience. It might be the case that, ce­teris paribus, the greater the range of phe­nom­e­nal in­ten­sity a crea­ture is ca­pa­ble of ex­pe­rienc­ing, the more morally valuable that crea­ture is. (That is to say, crea­tures ca­pa­ble of ex­pe­rienc­ing higher highs and lower lows are worth more, morally, than crea­tures whose ex­pe­rience tends to be neu­tral.)

Some peo­ple have the in­tu­ition that if in­ver­te­brates have the ca­pac­ity for valenced ex­pe­rience, their phe­nom­e­nal range would be much nar­rower than the phe­nom­e­nal range of ver­te­brates. For in­stance, Matt Ball writes, “So even if in­sects can have any sub­jec­tive ex­pe­rience, their most in­tense sen­sa­tion would be the palest hint of a feel­ing—a tiny frac­tion of the worst suffer­ing we can ex­pe­rience.” It’s not clear what ex­actly mo­ti­vates this view. It’s plau­si­ble that there are differ­ences of phe­nom­e­nal in­ten­sity across phy­lo­ge­net­i­cally dis­tant taxa, but it’s cer­tainly not ob­vi­ous that the differ­ence would be as stark as Ball sug­gests. It’s un­clear what fit­ness ad­van­tage the palest hint of a feel­ing could con­vey. Pain mo­ti­vates an­i­mals to do things like avoid bod­ily dam­age; plea­sure mo­ti­vates an­i­mals to do things like re­pro­duce. Sub­jec­tive ex­pe­riences so faint as to barely reg­ister would do a poor job mo­ti­vat­ing any­thing.

Per­haps the rea­son some peo­ple think in­ver­te­brates have a diminished range of phe­nom­e­nal in­ten­sity is that they think in­ver­te­brates are, in some sense, less con­scious than ver­te­brates. Here we must tread care­fully be­cause we are on shaky the­o­ret­i­cal ground. Ac­cord­ing to our defi­ni­tion, an en­tity is con­scious if and only if there is some­thing it feels like to be that en­tity, no mat­ter how strange or faint that phe­nomenol­ogy might be. So in our sense, con­scious­ness is bi­nary: ei­ther an en­tity is con­scious or it is not. Nonethe­less, there are cer­tain as­pects of con­scious­ness that ad­mit of gra­da­tions, and vari­a­tions of these gra­da­tions might be morally rele­vant.

There are at least three mun­dane ways in which con­scious­ness, loosely speak­ing, might come in de­grees. An en­tity that is con­scious might be con­scious all the time or only part of the time. (An­i­mal sleep cy­cles range from 2 to 20 hours a day.[14]) For an en­tity that is cur­rently con­scious, con­scious­ness might span many or few modal­ities. (Some crea­tures are sen­si­tive to differ­ences in light, sound, tem­per­a­ture, pres­sure, odor, bod­ily ori­en­ta­tion, and mag­netic field. Other crea­tures are sen­si­tive to far fewer sen­sory modal­ities.) For an en­tity that is cur­rently con­scious of a given sen­sory modal­ity, that modal­ity might be coarse-grained or fine-grained. (Within the vi­sion modal­ity, some crea­tures are only sen­si­tive to differ­ences in bright­ness, while other crea­tures are also sen­si­tive to hue and sat­u­ra­tion.)

In this loose sense, it ap­pears to be the case that if in­ver­te­brates like ne­ma­todes (round­worms), cnidar­i­ans (coral/​jel­lyfish/​anemones), porifer­ans (sponges), and an­nelids (earth­worms/​leeches) are con­scious, they are con­scious to a lesser de­gree than ver­te­brates. But for pre­cisely this rea­son, there is lit­tle ev­i­dence that these crea­tures are con­scious at all. Ac­cord­ing to many re­searchers, the role of con­scious­ness is to in­te­grate di­verse streams of in­for­ma­tion into one global workspace.[15] If an an­i­mal only re­ceives coarse-grained in­for­ma­tion from a sin­gle sen­sory modal­ity, there is no need to de­velop a global workspace. The in­ver­te­brates for which we have the best ev­i­dence of sen­tience, arthro­pods and coleoid cephalopods, do ap­pear to pro­cess dis­tinct sen­sory modal­ities into a unified whole.[16] It’s still pos­si­ble that these crea­tures are less con­scious (in the loose sense) than the av­er­age ver­te­brate, but it seems un­jus­tified to con­clude that they are dras­ti­cally less con­scious than the av­er­age ver­te­brate.

Another way to po­ten­tially get a han­dle on the phe­nom­e­nal in­ten­sity of non­hu­man ex­pe­rience is to con­sider again the evolu­tion­ary role that pain plays. Pain teaches us which stim­uli are nox­ious, how to avoid those stim­uli, and what we ought to do to re­cover from in­jury. Be­cause in­tense pain can be dis­tract­ing, an­i­mals in in­tense pain seem to be at a se­lec­tive dis­ad­van­tage com­pared to con­speci­fics not in in­tense pain. Thus, we might ex­pect evolu­tion to se­lect for crea­tures with pains just phe­nom­e­nally in­tense enough (on av­er­age) to play the pri­mary in­struc­tive role of pain. Hu­mans are among the most cog­ni­tively so­phis­ti­cated an­i­mals on the planet, plau­si­bly the an­i­mals most likely to pick up on pat­terns in sig­nals only weakly con­veyed. In gen­eral, less cog­ni­tively so­phis­ti­cated an­i­mals prob­a­bly re­quire stronger sig­nals for pat­tern-learn­ing. If pain is the sig­nal, then we might rea­son­ably ex­pect the phe­nom­e­nal in­ten­sity of pain to cor­re­late in­versely with cog­ni­tive so­phis­ti­ca­tion.[17] If that’s the case, hu­mans might ex­pe­rience (on av­er­age) the least in­tense pain in all the an­i­mal king­dom.[18]

A fi­nal con­sid­er­a­tion in­volves not the phe­nom­e­nal in­ten­sity of pain but its phe­nom­e­nal ex­ten­sion (that is, its felt du­ra­tion). Due to neu­rolog­i­cal differ­ences, phe­nom­e­nal ex­ten­sion might not be uniform across dis­similar taxa. Con­sider brain-pro­cess­ing speed and rates of sub­jec­tive ex­pe­rience, both loosely defined. An­i­mals with faster metabolisms and smaller body sizes tend, ac­cord­ing to some met­rics, to pro­cess in­for­ma­tion faster. Thus, there is some rea­son to think that smaller an­i­mals have, in gen­eral, faster sub­jec­tive ex­pe­riences. So a honey bee might ex­pe­rience one minute of ob­jec­tive time as longer, in some ro­bust sense of the term, than a hu­man would. If that’s true, then a given honey bee and a given hu­man ex­pe­rienc­ing a pain of the same phe­nom­e­nal in­ten­sity over the same ob­jec­tive du­ra­tion of time would not, ce­teris paribus, suffer equally. The honey bee would suffer more. Hence, we should not naively equate the phe­nom­e­nal ex­ten­sion of pain with its du­ra­tion ex­pressed in ob­jec­tive time. The take­away here is that the moral sig­nifi­cance of pains and plea­sures might be re­lated in im­por­tant ways to an en­tity’s pro­cess­ing speed. As with other ar­eas, more re­search is needed.

Other Mo­rally Sig­nifi­cant Properties

Range of phe­nom­e­nal in­ten­sity is prob­a­bly not the only in­trin­sic prop­erty rele­vant to moral weight. When philoso­phers dis­cuss gra­da­tions of moral sta­tus, they typ­i­cally in­voke a wider set of fea­tures. For in­stance, David De­grazia, an ethi­cist at Ge­orge Wash­ing­ton Univer­sity, de­scribes “a slid­ing-scale model, ac­cord­ing to which there are any num­ber of de­grees of moral sta­tus. On this view, the de­gree of con­sid­er­a­tion to which you are en­ti­tled—that is, the de­gree of moral weight your in­ter­ests are to re­ceive in com­par­i­son with oth­ers’ com­pa­rable in­ter­ests—de­pends on the de­gree of your cog­ni­tive, af­fec­tive, and so­cial com­plex­ity” (em­pha­sis added).[19] Later in the same pa­per he writes, “Per­son­hood… is a cluster con­cept that serves as a sum­mary place­holder for other con­cepts such as moral agency, au­ton­omy, the ca­pac­ity for in­ten­tional ac­tion, ra­tio­nal­ity, self-aware­ness, so­cia­bil­ity, and lin­guis­tic abil­ity. But most… of these prop­er­ties can be rea­son­ably un­der­stood as com­ing in de­grees; and many of them… are found to some de­gree in non­hu­man an­i­mals. Now, if these morally rele­vant prop­er­ties come in de­grees and cross species bound­aries, it is nat­u­ral to judge that the moral sta­tus based on these prop­er­ties also comes in de­grees while ex­tend­ing be­yond our species—sup­port­ing the slid­ing-scale model of moral sta­tus” (em­pha­sis added).[20]

How do in­ver­te­brates stack up against ver­te­brates ac­cord­ing to these crite­ria? It de­pends on the in­ver­te­brate. Moon jel­lyfish don’t dis­play much cog­ni­tive, af­fec­tive, or so­cial com­plex­ity, and there’s lit­tle rea­son to sus­pect they pos­sess moral agency, au­ton­omy, the ca­pac­ity for in­ten­tional ac­tion, ra­tio­nal­ity, self-aware­ness, or lin­guis­tic abil­ity. Other in­ver­te­brates are more im­pres­sive. Con­sider the large or­der Hy­menoptera (which in­cludes wasps, bees, and ants). One liter­a­ture re­view doc­u­mented 59 dis­tinct be­hav­ior types in honey bees; that num­ber com­pares fa­vor­ably against many mam­malian species, such as the North Amer­i­can moose (at 22), De Brazza mon­keys (at 44), and bot­tlenose dolphins (at 123). A sep­a­rate study shows that honey bees ex­hibit more self-con­trol (defined as the ten­dency to choose large de­layed re­wards over small im­me­di­ate re­wards) than rats and pi­geons. Another re­cent study demon­strates that wasps are ca­pa­ble of tran­si­tive in­fer­ence. Many of these an­i­mals dis­play ex­traor­di­nary so­cial com­plex­ity. Some ants live in su­per­colonies con­tain­ing mil­lions of in­di­vi­d­u­als. The effects of so­cial de­pri­va­tion can be dras­tic. So­cial iso­la­tion in­creases ag­gres­sion in hon­ey­bees, re­duces lifes­pan in ants, and de­stroys wasps’ abil­ity to rec­og­nize faces. There is even ev­i­dence of af­fec­tive com­plex­ity in or­der Hy­menoptera. Agi­tated honey bees ex­hibit the same sorts of pes­simistic cog­ni­tive bi­ases that anx­ious mam­mals do.

None of this is to say that ants, wasps, and bees en­joy the same moral sta­tus as cows and pigs. It’s still plau­si­ble that in­sects are worth less, morally, than mam­mals. But the case that in­ver­te­brates are, as a rule, worth far less than ver­te­brates is quite weak. The in­ver­te­brate taxa for which we have the best ev­i­dence of sen­tience, coleoid cephalopods and arthro­pods, con­tain mem­bers ca­pa­ble of cog­ni­tive, so­cial, and af­fec­tive com­plex­ity that ri­vals many ver­te­brate species. And if these in­ver­te­brates can suffer, there is so far lit­tle rea­son to think that they suffer ex­po­nen­tially less than typ­i­cal ver­te­brates.

Limit­ing Factors

When con­sid­er­ing the scale of a prob­lem, it is also pru­dent to ex­am­ine the limit­ing fac­tors that con­strain the de­gree to which in­ter­ven­tions in the near-term are able to tackle the prob­lem. For ex­am­ple, there may be tremen­dous, eas­ily pre­ventable suffer­ing oc­cur­ring on a far-off planet in our galaxy. We might come to de­tect this suffer­ing with next-gen­er­a­tion as­tro­nom­i­cal equip­ment. But if the tech­nol­ogy to ac­tu­ally re­duce the far-off suffer­ing (e.g., by send­ing space­craft to the planet) is still cen­turies away, then for pur­poses of near-term in­ter­ven­tions, the scale of the suffer­ing is ir­rele­vant. Of course, in the long-term, nearly all limit­ing fac­tors are muta­ble, so the cost of elimi­nat­ing a limit­ing fac­tor is just one more in­put into a tra­di­tional cost-effec­tive­ness anal­y­sis.[21] Still, the gen­eral les­son should be rec­og­niz­able: there’s no point buy­ing bed­nets to­day if the ship to de­liver them isn’t go­ing to be ready for a hun­dred years.

This les­son is par­tic­u­larly rele­vant for in­ver­te­brate welfare. Take some ex­tremely nu­mer­ous group of po­ten­tially sen­tient in­ver­te­brates, say arthro­pods. Even as­sign­ing an egre­giously low cre­dence to the claim that arthro­pods have the ca­pac­ity for morally sig­nifi­cant valenced ex­pe­rience and ad­just­ing down­ward for moral weight, one should still be­lieve that the ex­pected moral worth of the phy­lum Arthro­poda is com­pa­rable to the ex­pected moral worth of many classes of ver­te­brates.[22] Tak­ing a more rea­son­able (though still low) view of the pos­si­bil­ity of morally sig­nifi­cant arthro­pod ex­pe­rience re­sults in an ex­pected moral worth higher than any class of ver­te­brates. Does that nec­es­sar­ily mean that we should start pour­ing tens of mil­lions of dol­lars into in­ver­te­brate welfare? No.

Put sim­ply, there are a va­ri­ety of limit­ing fac­tors that will con­strain the use­ful­ness of large amounts of money in this area for many years to come. The biggest limit­ing fac­tor is un­cer­tainty. We don’t know enough about in­ver­te­brates to be able to judge with much con­fi­dence which in­ver­te­brates (if any) are sen­tient. We don’t know enough about the life his­tory of most in­ver­te­brates to know which in­ter­ven­tions would be most benefi­cial. Of the in­ter­ven­tions that do seem po­ten­tially promis­ing (e.g., hu­mane in­sec­ti­cides) we don’t know enough about the flow-through effects to recom­mend the in­ter­ven­tions at scale.[23] Even if we were in a po­si­tion to recom­mend large-scale in­ter­ven­tions, we don’t know enough about pub­lic at­ti­tudes to­ward in­ver­te­brates to know whether or not ad­vo­cat­ing for in­ver­te­brate welfare would be net-nega­tive for the effec­tive al­tru­ism move­ment as a whole. And so on.

All this un­cer­tainty trans­lates to few ac­tion­able in­ter­ven­tions other than ad­di­tional in­ves­ti­ga­tion. More­over, there are very few re­searchers and even fewer or­ga­ni­za­tions ex­plic­itly think­ing about in­ver­te­brate welfare.[24] Thus, in the short-term, the in­ver­te­brate welfare cause area will only be able to ab­sorb a mod­est amount of fund­ing.[25]

Although in the long-term we should work to dis­man­tle these limit­ing fac­tors, in the near-term they may con­tribute to, rather than de­tract from, the case for in­ver­te­brate welfare. Be­cause the ca­pac­ity for in­ver­te­brate welfare to ab­sorb ad­di­tional fund­ing is so limited, it’s pos­si­ble to fully fund (for the near-term) a po­ten­tially im­por­tant cause area for a rel­a­tively small sum of money. In that sense, in­ver­te­brate welfare is a steal.

The Ev­i­dence for In­ver­te­brate Sentience

Some Caveats

First, the goal of this sec­tion is not to defini­tively con­vince any­one that in­ver­te­brates are sen­tient. The aim is merely to make the idea of in­ver­te­brate sen­tience some­what plau­si­ble, where ‘some­what plau­si­ble’ is com­pat­i­ble with cre­dences well be­low 50%. Be­cause there are so many in­ver­te­brates, even a rel­a­tively low cre­dence in the propo­si­tion that in­ver­te­brates are sen­tient will, when cou­pled with a few ba­sic as­sump­tions dis­cussed el­se­where, gen­er­ate a high ex­pected moral value.

Se­cond, limited ev­i­dence of sen­tience should not be con­fused with limited sen­tience. The sci­en­tific liter­a­ture on in­ver­te­brate sen­tience is young and in­com­plete and does not yet rep­re­sent our best un­der­stand­ing of ev­ery group of in­ver­te­brates. More re­search is needed.

Third, this overview is in­ten­tion­ally cur­sory. A com­pre­hen­sive overview is sim­ply not fea­si­ble in a length suit­able for the EA Fo­rum. Whole books have been writ­ten about much smaller groups of an­i­mals. Due to space con­straints, we have con­densed the re­sults of dozens of stud­ies into a few pages worth of ma­te­rial. For a ful­ler ac­count, see our sum­mary of find­ings (part 1, part 2) or our In­ver­te­brate Sen­tience Table.

Fourth, the type of ev­i­dence that one con­sid­ers rele­vant to in­ver­te­brate sen­tience de­pends on the method­ol­ogy one adopts for in­ves­ti­gat­ing the ques­tion. We en­dorse the method­ol­ogy em­ployed by philoso­pher Michael Tye in his 2016 book Tense Bees and Shell-Shocked Crabs. Tye uses an ar­gu­ment form called in­fer­ence to the best ex­pla­na­tion. The strat­egy is sim­ple. Con­sider the be­hav­ior of some group of an­i­mals. If the best ex­pla­na­tion for that be­hav­ior is that those an­i­mals are con­scious, then, in the ab­sence of defeaters, one is li­censed to pre­fer the ex­pla­na­tion that those an­i­mals are con­scious to al­ter­na­tive ex­pla­na­tions that don’t in­voke con­scious­ness.[26] For more on in­fer­ence to the best ex­pla­na­tion, see our first and sec­ond posts.

Fifth, the ev­i­dence pre­sented here is sug­ges­tive, not defini­tive. There are in fact many al­ter­na­tive ex­pla­na­tions for the be­hav­iors de­scribed be­low that do not in­voke con­scious­ness. We dis­cuss these al­ter­na­tives, as well as other po­ten­tial defeaters, in our forth­com­ing coun­ter­ar­gu­ments post.

Fi­nally, due to the ex­traor­di­nary di­ver­sity of in­ver­te­brates, there are few pieces of in­for­ma­tion that might qual­ify as ev­i­dence for in­ver­te­brate sen­tience in gen­eral.[27] Nev­er­the­less, it is per­haps worth not­ing that nearly all in­ver­te­brates with­draw from po­ten­tially harm­ful stim­uli, and no­ci­cep­tion, the neu­ral pro­cess of en­cod­ing and pro­cess­ing po­ten­tially harm­ful stim­uli, is widely con­served through­out the an­i­mal king­dom, in­clud­ing in in­ver­te­brates.[28] Nearly all in­ver­te­brates are ca­pa­ble of some form of learn­ing, with many in­ver­te­brates dis­play­ing long-term be­hav­ior al­ter­a­tion in re­sponse to harm­ful stim­uli. Still, there is rel­a­tively lit­tle to be gained from in­ves­ti­gat­ing sen­tience at such a high level of gen­er­al­ity. Bet­ter to an­a­lyze spe­cific groups of in­ver­te­brates. We turn then to three case stud­ies: coleoid cephalopods, de­ca­pod crus­taceans, and eu­so­cial in­sects.

Case Studies

Coleoid Cephalopods

Coleoid cephalopods en­com­pass squid, cut­tlefish, and oc­to­puses. Coleoid cephalopods are soft-bod­ied, ex­clu­sively marine an­i­mals char­ac­ter­ized by bilat­eral body sym­me­try, a promi­nent head, and eight or ten highly de­vel­oped ten­ta­cles. Coleoid cephalopods are mol­luscs, and, like all mol­luscs, they evolved from crea­tures with shells. Un­like their ex­tant sister group, the nau­tiloid cephalopods, which re­tain an outer shell for pro­tec­tion and to which they are only dis­tantly re­lated, coleoid cephalopods have ei­ther in­ter­nal­ized or elimi­nated their shells. Coleoid cephalopods first ap­pear in the fos­sil record a lit­tle more than 300 mil­lion years ago, al­though given the fact that they are soft-bod­ied, it’s pos­si­ble they split from other cephalopods some­what ear­lier. Coleoid cephalopods are di­vided into two ma­jor su­per­orders, the ten-ten­ta­cle de­capod­iformes (cut­tlefish and most squid) and the eight-ten­ta­cle oc­topod­iformes (oc­to­puses and vam­pire squid).[29]

Coleoid cephalopods are uni­ver­sally rec­og­nized as the most in­tel­li­gent in­ver­te­brates. Oc­to­puses have roughly five hun­dred mil­lion neu­rons, and al­though an as­ton­ish­ing 60% of these neu­rons are lo­cated in the ten­ta­cles, oc­to­puses still have a rec­og­niz­able cen­tral brain that pro­cesses and in­te­grates ex­te­ro­cep­tive and in­te­ro­cep­tive sen­sory in­for­ma­tion.[30] Oc­to­puses are no­to­ri­ously clever tool users. In ad­di­tion to countless lab­o­ra­tory anec­dotes, oc­to­puses in the wild have been ob­served as­sem­bling co­conuts into portable defen­sive shelters.[31] Oc­to­puses also have a keen sense of ob­ject per­ma­nence: they will make de­tours to get at prey seen through a trans­par­ent bar­rier, even if the de­tour takes them out of sight of their tar­get.[32]

Cut­tlefish de­ploy a wide va­ri­ety of chro­matic, tex­tu­ral, pos­tu­ral, and lo­co­mo­tor el­e­ments to com­mu­ni­cate with preda­tors, prey, and con­speci­fics, and there is ev­i­dence that they pos­sess a so­phis­ti­cated the­ory of mind.[33] Dur­ing courtship male cut­tlefish en­gage in a re­mark­able form of tac­ti­cal de­cep­tion with ri­val males: si­mul­ta­neous dual gen­der sig­nal­ling. A male will po­si­tion it­self be­tween a ri­val male and a po­ten­tial mate. On the side of its man­tle fac­ing the po­ten­tial mate, the de­cep­tive male will pro­duce typ­i­cal chro­matic courtship pat­terns. But on the side of its man­tle fac­ing the ri­val male, it will mimic typ­i­cal fe­male dis­plays, thus con­fus­ing the ri­val and sig­nifi­cantly re­duc­ing the odds that the ri­val male will at­tempt to dis­rupt cop­u­la­tion.

Jen­nifer Mather, a biol­o­gist and psy­chol­o­gist at the Univer­sity of Leth­bridge and a pi­o­neer in cephalo­pod re­search, ar­gues that coleoid cephalopods plau­si­bly satisfy the ‘global workspace’ crite­rion on con­scious­ness. Ac­cord­ing to this pop­u­lar the­ory of con­scious­ness, what’s re­quired (and suffi­cient) for con­scious­ness is the in­te­grated rep­re­sen­ta­tion of var­i­ous sen­sory in­puts com­pet­ing for an or­ganism’s at­ten­tion. Cephalopods’ “rich dis­crim­i­na­tory be­hav­ior” and “do­main gen­er­al­ity of learn­ing” are, in Mather’s words, ev­i­dence of “pri­mary con­scious­ness.”

In 2005 the Scien­tific Panel on An­i­mal Health and Welfare of the Euro­pean Union con­cluded that cephalopods “have a ner­vous sys­tem and rel­a­tively com­plex brain similar to many ver­te­brates, and suffi­cient in struc­ture and func­tion­ing for them to ex­pe­rience pain.”[34] As a re­sult of this con­clu­sion, EU mem­ber states opted to give cephalopods used for sci­en­tific re­search the same le­gal pro­tec­tion that was pre­vi­ously af­forded only to ver­te­brates (Direc­tive 2010/​63/​EU).

De­ca­pod Crustaceans

De­ca­pod crus­taceans en­com­pass prawns, shrimp, crayfish, crabs, and lob­sters. De­ca­pod crus­taceans are ten-footed arthro­pods char­ac­ter­ized by the cara­pace ex­tend­ing from their tho­rax to their head.[35] They can be found both on land and at sea in a wide range of habitats wor­ld­wide. Crus­taceans are a com­mer­cially im­por­tant group of an­i­mals. As noted above, hun­dreds of billions of crus­taceans are slaugh­tered for food ev­ery year. (Most crus­taceans con­sumed by hu­mans are de­capods.[36]) De­ca­pod crus­taceans have a long evolu­tion­ary his­tory. Prawns first ap­pear in the fos­sil record in the Tri­as­sic Pe­riod, shrimp and crabs first ap­pear in the Juras­sic, and lob­sters first ap­pear in the Cre­ta­ceous.

De­ca­pod crus­taceans en­gage in com­plex mo­ti­va­tional trade­offs that demon­strate the sort of be­hav­ioral plas­tic­ity one would ex­pect from crea­tures with the ca­pac­ity for valenced ex­pe­rience (and that one would not ex­pect from crea­tures with­out the ca­pac­ity for valenced ex­pe­rience). For ex­am­ple, in a lab­o­ra­tory set­ting, her­mit crabs will aban­don their shells if they are sub­jected to a mild shock. Ini­tially, such be­hav­ior was thought to be purely re­flex­ive. How­ever, re­cent ex­per­i­ments show the crabs are sig­nifi­cantly less likely to aban­don their shells af­ter shock if the odor of a preda­tor is pre­sent. The fact that the crabs re­main in their shells when the odor of a preda­tor is pre­sent sug­gests that the be­hav­ior is not re­flex­ive. A nat­u­ral ex­pla­na­tion is that the crabs weigh the pain of the shock against the fear of a preda­tor, thus in­cor­po­rat­ing differ­ent in­ter­ests and de­mands into a unified util­ity func­tion. Such in­te­gra­tion is of­ten con­sid­ered a dis­tinc­tive at­tribute of con­scious­ness.

Another ex­am­ple: shore crabs gen­er­ally avoid well-lit ar­eas, prefer­ring to hide in dark en­vi­ron­ments such as those found un­der rocks. Given the choice be­tween two cham­bers in a lab­o­ra­tory set­ting, one brightly lit and the other dark, the crabs will uni­ver­sally choose the dark cham­ber. How­ever, if the dark cham­ber is rigged to de­liver a mild shock, the crabs will be­gin to opt for the nor­mally avoided well-lit cham­ber. The crabs do so in in­creas­ing num­bers (and in­creas­ingly quickly) as the num­ber of tri­als in­creases. A com­pel­ling ex­pla­na­tion of this be­hav­ior is that the crabs feel pain, then learn to avoid the pain by choos­ing the op­po­site, oth­er­wise un­de­sir­able cham­ber.

De­ca­pod crus­taceans also ap­pear to lead com­plex emo­tional lives. For in­stance, stress-in­duced avoidance be­hav­ior in crayfish bears a strik­ing re­sem­blance to mam­malian anx­iety. A 2014 study demon­strated that shocked crayfish de­velop an ex­tended, con­text-in­de­pen­dent aver­sion to light.[37] (The shocks were not as­so­ci­ated with lev­els of illu­mi­na­tion.) In con­trast, un­shocked crayfish, though prefer­ring the dark, were happy to ex­plore both illu­mi­nated and unillu­mi­nated ar­eas of their en­vi­ron­ment. Most im­por­tantly, in­ject­ing the shocked crayfish with the anx­iolytic drug chlor­diazepox­ide (used to treat anx­iety in hu­mans) elimi­nated the aver­sion to light.[38] In hu­mans, anx­iety is of­ten as­so­ci­ated with dan­ger that is per­ceived to be un­avoid­able[39] or situ­a­tions in which the threat is am­bigu­ous or un­known.[40] The elec­tric shocks ap­plied to the crayfish fit this de­scrip­tion. In hu­mans, anx­iety is as­so­ci­ated with gen­er­al­ized fear, that is, in­creased fear of un­re­lated stim­uli. The shocked crayfish ap­peared to ex­hibit in­creased fear of light that is un­re­lated to the source of stress. In hu­mans, anx­iety is re­duced by anx­iolytic drugs. In crayfish, anx­iety-like be­hav­ior is re­duced by anx­iolytic drugs. The most nat­u­ral ex­pla­na­tion of this phe­nomenon is that crayfish, like hu­mans, are ca­pa­ble of ex­pe­rienc­ing nega­tively valenced emo­tional states.

Eu­so­cial Insects

Eu­so­cial in­sects are group-liv­ing an­i­mals char­ac­ter­ized by re­pro­duc­tive di­vi­sion of la­bor, co­op­er­a­tive care of young, and over­lap­ping adult gen­er­a­tions. All ants and ter­mites are eu­so­cial, as are many bees, wasps, and aphids.[41] Be­cause the ge­netic fit­ness of ster­ile eu­so­cial work­ers is de­ter­mined by the suc­cess of the colony and be­cause hives and colonies are ca­pa­ble of com­plex group de­ci­sion-mak­ing, eu­so­cial in­sects are some­times thought to con­sti­tute su­per­or­ganisms. Although eu­so­cial­ity is rare, eu­so­cial in­sects are among the most suc­cess­ful an­i­mals on the planet, dom­i­nat­ing many ter­res­trial habitats and of­ten oc­cu­py­ing cor­ner­stone ecolog­i­cal niches. The com­par­i­son to hu­man so­cieties is in­escapable. Eu­so­cial in­sects typ­i­cally live in densely pop­u­lated, in­tri­cately tun­neled hives or mounds. Colonies of­ten em­ploy spe­cial­ized la­bor castes and de­pend on ex­ten­sive so­cial com­mu­ni­ca­tion, in­clud­ing rel­a­tively com­plex forms of ob­ser­va­tional learn­ing. The re­sult is a re­mark­able ar­ray of mul­ti­faceted colony-level ac­tivity, such as aphid ‘farm­ing’ and corpse man­age­ment.

In ad­di­tion to im­pres­sive colony-level be­hav­iors, in­di­vi­d­ual eu­so­cial in­sects are sur­pris­ingly in­tel­li­gent. Ants learn quickly and do not for­get eas­ily. Honey bees are able to com­mu­ni­cate the dis­tance, di­rec­tion, and rel­a­tive re­ward-to-dan­ger ra­tio of nearby flower patches to hive­mates us­ing their fa­mous wag­gle dance. Ants and bees are both ca­pa­ble of us­ing tools flex­ibly. Fun­nel ants use ar­tifi­cial de­bris to trans­port liquid food to the nest, adopt­ing differ­ent ma­te­ri­als for differ­ent types of liquid in or­der to op­ti­mize han­dling and soak­ing prop­er­ties. In an­other re­cent study re­searchers trained bum­ble bees to see that a ball could be used to dis­pense a re­ward. In sub­se­quent iter­a­tions of the ex­per­i­ment, the bees in­de­pen­dently learned to solve the task more effi­ciently by us­ing a ball po­si­tioned more closely to the tar­get, even though the ball was a differ­ent color.[42] Both ants and bees en­gage in con­tex­tual learn­ing. For in­stance, ants can be trained to as­so­ci­ate the scent of an ant from an­other colony with a food re­ward and once trained will ap­proach the odor in an ap­pet­i­tive con­text. How­ever, the con­di­tioned ants are not eas­ily fooled. When a non-nest­mate ant is pre­sent alongside the odor, the con­di­tioned ants re­vert to their ag­gres­sive be­hav­ior.[43] Similarly, honey bees can come to un­der­stand that when a cer­tain color is pre­sented to them, odor A pre­dicts a su­crose re­ward and odor B does not, but when a differ­ent color is pre­sented, the re­la­tion­ship be­tween the odors is re­versed.

There is even ev­i­dence of metacog­ni­tive abil­ities in eu­so­cial in­sects. Us­ing the “un­cer­tain re­sponse” paradigm, one study tasked honey bees with dis­crim­i­nat­ing be­tween two stim­uli. A cor­rect an­swer earned a re­ward (su­crose) and an in­cor­rect an­swer earned a pun­ish­ment (qui­nine). When given the choice to opt out, honey bees were found to opt out more of­ten when the trial was difficult (when the honey bee was pro­por­tionately more likely to re­ceive a pun­ish­ment than a re­ward). The honey bees on av­er­age im­proved their suc­cess-to-failure ra­tio when given the op­tion to opt out of tri­als.[44] When search­ing for a new nest site, in­di­vi­d­ual ants ad­just their be­hav­ior ac­cord­ing to their rel­a­tive con­fi­dence. They em­ploy a “highly so­phis­ti­cated ‘copy-when-un­cer­tain’ so­cial learn­ing strat­egy similar to that ob­served in a few ver­te­brate species:” when their con­fi­dence is high, ants tend to act on their own ini­ti­a­tive, but when they are un­cer­tain, they tend to copy the ac­tions of their nest­mates.[45] Another study found that ants up­reg­u­late pheromone trail de­po­si­tion in re­sponse to changes in the lo­ca­tion of food. In an ex­per­i­ment with a T-maze, re­searchers trained ants to a feeder lo­ca­tion, then al­tered the en­vi­ron­ment by chang­ing the feeder lo­ca­tion to the other arm of the T-maze. After find­ing the new food source, ants up­reg­u­lated pheromone de­po­si­tion if they had made a wrong choice. Ad­di­tion­ally, the re­searchers found that out­go­ing ants that went on to make an er­ror de­posited less pheromone. This seems to im­ply that the ants can mea­sure the re­li­a­bil­ity of their own mem­o­ries and re­spond ac­cord­ingly by de­posit­ing more or less pheromones.[46]

Neglectedness

EA Space

In­ver­te­brate welfare is mostly ig­nored within the effec­tive al­tru­ism com­mu­nity. De­spite the fact that in­ver­te­brates com­prise more than 99.9% of all an­i­mals, there is no sin­gle or­ga­ni­za­tion in the effec­tive an­i­mal ac­tivism move­ment ex­clu­sively work­ing to pro­mote in­ver­te­brate well-be­ing. In the effec­tive al­tru­ism com­mu­nity there are only two or­ga­ni­za­tions that de­vote a sig­nifi­cant por­tion of their (mod­est) bud­gets to in­ver­te­brate welfare. Wild An­i­mal Ini­ti­a­tive is cur­rently con­duct­ing a re­search pro­ject to in­ves­ti­gate the fea­si­bil­ity of a hu­mane in­sec­ti­cide pro­gram. The other or­ga­ni­za­tion is Re­think Pri­ori­ties, the group that pro­duced this re­port. There are also a hand­ful of in­de­pen­dent EA re­searchers pro­mot­ing the cause area. Brian To­masik has writ­ten ex­ten­sively on in­ver­te­brate suffer­ing. Max Carpen­dale, an in­de­pen­dent re­searcher at the EA ho­tel and past con­trib­u­tor to Re­think Pri­ori­ties’ work on in­ver­te­brate welfare, has also writ­ten about in­ver­te­brate sen­tience.

Sev­eral other or­ga­ni­za­tions in EA space are aware of the po­ten­tial mag­ni­tude of in­ver­te­brate welfare. An­i­mal Ethics has writ­ten about an­i­mal sen­tience, in­clud­ing in­ver­te­brate sen­tience, as well as an­i­mal ex­ploita­tion, in­clud­ing the ex­ploita­tion of in­ver­te­brates. Foun­da­tional Re­search In­sti­tute and Effec­tive Altru­ism Foun­da­tion are closely al­igned with To­masik’s views on in­ver­te­brate sen­tience. Both An­i­mal Char­ity Eval­u­a­tors and the Open Philan­thropy Pro­ject have pre­vi­ously ex­pressed in­ter­est in re­search that in­ves­ti­gates the im­por­tance of in­ver­te­brate welfare. Fau­n­a­lyt­ics and An­i­mal Equal­ity have also oc­ca­sion­ally writ­ten about in­ver­te­brates.

Based on the above, I es­ti­mate that the effec­tive al­tru­ism com­mu­nity as a whole cur­rently com­mits no less than $150,000 per year and no more than $300,000 per year to in­ver­te­brate welfare.[47] Be­cause there are no or­ga­ni­za­tions ex­clu­sively work­ing on in­ver­te­brate welfare, an ex­act es­ti­mate de­pends on the way the pro­por­tion of var­i­ous re­search bud­gets is al­lo­cated to in­ver­te­brate welfare. Ad­di­tion­ally, the ex­act num­ber ap­pears prone to pretty se­vere year-on-year fluc­tu­a­tions. Given cer­tain de­vel­op­ments, the num­ber could plau­si­bly fall to ~$0 in 2020. By way of com­par­i­son, Open Phil recom­mended nearly $28 mil­lion in an­i­mal welfare grants in 2018.[48] If we as­sume that Open Phil ac­counts for one-half to two-thirds of to­tal effec­tive an­i­mal ac­tivism spend­ing, that puts the per­centage of money spent on in­ver­te­brates in effec­tive an­i­mal ac­tivism be­tween 0.27% and 0.71%.

Non-EA Space

In­ver­te­brate welfare is also gen­er­ally ne­glected out­side the effec­tive al­tru­ism com­mu­nity. Ex­clud­ing EA or­ga­ni­za­tions, there are per­haps fewer than half a dozen an­i­mal rights groups in the an­glo­phone world that take in­ver­te­brate welfare se­ri­ously. PETA is one of them. PETA cam­paigns against eat­ing crus­taceans, wear­ing silk, own­ing her­mit crabs, and kil­ling house­hold pest in­sects. Another im­por­tant, albeit limited, or­ga­ni­za­tion is Crus­tacean Com­pas­sion. Crus­tacean Com­pas­sion is a UK-based char­ity cam­paign­ing to have crabs, lob­sters and other de­capods in­cluded in an­i­mal welfare leg­is­la­tion on the grounds that crus­taceans feel pain. Among other goals, Crus­tacean Com­pas­sion hopes to repli­cate the live boil ban re­cently en­acted in Switzer­land. FishCount, a UK-based group pro­mot­ing more hu­mane com­mer­cial fish­ing, sup­ports these goals. Viva!, an­other UK-based an­i­mal rights or­ga­ni­za­tion, also cam­paigns on be­half of lob­sters. Or­ga­ni­za­tions that pro­mote strict ve­g­anism, in­clud­ing ab­sten­tion from honey and silk, such as The Ve­gan So­ciety, also take the in­ter­ests of in­ver­te­brates into ac­count. Many Dharmic re­li­gions, but es­pe­cially Jainism, ad­vise ad­her­ents to min­i­mize harm to all liv­ing things, in­clud­ing in­ver­te­brates.

Con­ser­va­tion Groups

In ad­di­tion to an­i­mal welfare and an­i­mal rights or­ga­ni­za­tions, there are also dozens of con­ser­va­tion groups that tar­get in­ver­te­brates. It is difficult to know how to as­sess these bod­ies. For one, it’s not clear that any of the or­ga­ni­za­tions cov­ered in this sec­tion be­lieve that in­ver­te­brates pos­sess in­trin­sic moral value or that they have the ca­pac­ity for valenced ex­pe­rience. Most of the or­ga­ni­za­tions em­pha­size the in­stru­men­tal value that many in­ver­te­brates (e.g., in­sect pol­li­na­tors) provide to ecosys­tem sta­bil­ity or the aes­thetic value that cer­tain iconic in­ver­te­brate species (e.g., monarch but­terflies) provide to hu­mans. More­over, it’s un­clear if the cam­paigns in which these or­ga­ni­za­tions en­gage are net-pos­i­tive for in­ver­te­brates as a whole. Nonethe­less, these groups do pos­sess var­i­ous forms of ex­per­tise re­lat­ing to in­ver­te­brates and could po­ten­tially make for good part­ners for ad­vo­cacy, re­search, or on-the-ground in­ter­ven­tions.

There are two gen­eral pur­pose in­ver­te­brate con­ser­va­tion groups in the an­glo­phone world: the Xerces So­ciety in North Amer­ica and Buglife in Europe. How­ever, there are dozens, per­haps as many as a hun­dred, con­ser­va­tion char­i­ties that spe­cial­ize in par­tic­u­lar groups of in­ver­te­brates. For ex­am­ple (and just to name a few), there are drag­on­fly char­i­ties: The Dragon­fly So­ciety of the Amer­i­cas and the Bri­tish Dragon­fly So­ciety. There are bee char­i­ties: The Honey­bee Con­ser­vancy, Planet Bee Foun­da­tion, Pol­li­na­tor Part­ner­ship, and the Bum­ble­bee Con­ser­va­tion Trust. And there are but­terfly char­i­ties: Save Our Monar­chs, North Amer­i­can But­terfly As­so­ci­a­tion, But­terfly Con­ser­va­tion, and the Lepi­dopter­ists’ So­ciety.

Academia

Although it is difficult to es­ti­mate what per­centage of aca­demics con­duct re­search on in­ver­te­brate welfare rel­a­tive to other groups of an­i­mals, it is clear that in­ver­te­brate welfare is largely ne­glected in academia. That’s not to say that in­ver­te­brates them­selves are ne­glected. Many model or­ganisms are in­ver­te­brates. The fruit fly Drosophila melanogaster, the sea slug Aplysia cal­ifor­nica, and the ne­ma­tode Caenorhab­di­tis el­e­gans, are among the best un­der­stood an­i­mals on the planet. One rea­son these crea­tures are so widely stud­ied is the be­lief that fruit flies, sea slugs, and ne­ma­todes are in­ca­pable of ex­pe­rienc­ing pain. Many ex­per­i­men­tal de­signs that would never be sanc­tioned for use on mam­malian sub­jects are rou­tinely con­ducted on in­ver­te­brates with­out eth­i­cal over­sight.

A hand­ful of aca­demic re­searchers do take the ques­tion of in­ver­te­brate welfare se­ri­ously, and an even smaller group is ac­tively in­ves­ti­gat­ing in­ver­te­brate sen­tience. Robert El­wood, pro­fes­sor emer­i­tus in the school of biolog­i­cal sci­ences at Queen’s Univer­sity Belfast, has been ad­vanc­ing the no­tion that crus­taceans ex­pe­rience pain and stress for over a decade. Lynne Sned­don, di­rec­tor of biovet­eri­nary sci­ence at the Univer­sity of Liver­pool, also pro­motes the idea that a wide va­ri­ety of aquatic an­i­mals, in­clud­ing crus­taceans, demon­strate the po­ten­tial for pain per­cep­tion. An­thony Rowe, an an­i­mal welfare officer at CSIRO, be­lieves use of de­ca­pod crus­taceans in re­search should re­quire eth­i­cal re­view. Jen­nifer Mather, an ex­pert in cephalo­pod cog­ni­tion at the Univer­sity of Leth­bridge, has long ar­gued that oc­to­puses, squid, and cut­tlefish ap­pear to be con­scious. Robyn J. Crook, an evolu­tion­ary biol­o­gist and be­hav­ioral neu­ro­scien­tist at San Fran­cisco State Univer­sity, runs a lab study­ing sen­sa­tion, emo­tion, and cog­ni­tion in cephalopods, with an aim to provide em­piri­cal sup­port for reg­u­la­tion gov­ern­ing the use of com­plex in­ver­te­brates in sci­en­tific re­search. Shel­ley Adamo, a neu­ro­biol­o­gist at Dalhousie Univer­sity, has re­viewed the ev­i­dence for in­sect sen­tience and was asked to tes­tify be­fore a Cana­dian sen­ate com­mit­tee in 2003 as to whether in­ver­te­brates feel pain. An­drew Bar­ron, a neu­roethol­o­gist and ARC Fu­ture Fel­low at Mac­quarie Univer­sity, ar­gues that in­sects have the ca­pac­ity for sub­jec­tive ex­pe­rience.[49]

Bar­ri­ers to Attention

Hu­man psy­cholog­i­cal heuris­tics con­spire to make em­pathiz­ing with in­ver­te­brates ex­tremely difficult. Com­pared to house­hold pets, farmed an­i­mals, and iconic wild species, most in­ver­te­brates are small and alien-look­ing. Many in­ver­te­brates are as­so­ci­ated in the pop­u­lar mind with dis­ease or un­clean­li­ness. En­coun­ters with in­ver­te­brate of­ten pro­duce feel­ings of dis­gust, anx­iety, or fear. Th­ese re­ac­tions can al­ter the con­tours of sci­en­tific in­ves­ti­ga­tion. Tax­o­nomic bias is ram­pant in con­ser­va­tion biol­ogy and bio­di­ver­sity re­search. Large, charis­matic species are wildly over-rep­re­sented in sci­en­tific stud­ies, and this skew is driven largely by so­cietal prefer­ences. (In­sects are par­tic­u­larly un­der-rep­re­sented.) Even when in­ver­te­brates are not ig­nored, their welfare typ­i­cally is. Our psy­cholog­i­cal heuris­tics ex­plain some of this ne­glect, but it is also due to the na­ture of the sub­ject. In­ver­te­brate sen­tience re­search lies at the in­ter­sec­tion of philos­o­phy, biol­ogy, and neu­ro­science. As Max Carpen­dale puts it, “Many in­ver­te­brate biol­o­gists who might oth­er­wise have a lot to con­tribute in the area are not philo­soph­i­cally in­clined, and have not thought about the eth­i­cal im­pli­ca­tions of their knowl­edge, and so be­come con­fused about the ques­tion of in­ver­te­brate sen­tience.” With these bar­ri­ers to at­ten­tion in place, it is no sur­prise that in­ver­te­brate welfare is a highly ne­glected cause area.

Tractability

How Should We Eval­u­ate the Tractabil­ity of In­ver­te­brate Welfare?

Im­prov­ing in­ver­te­brate welfare will un­doubt­edly be difficult. How difficult? No one knows. Very few or­ga­ni­za­tions and re­searchers have se­ri­ously in­ves­ti­gated cost-effec­tive in­ter­ven­tions to im­prove the lives of in­ver­te­brates, and those that have se­ri­ously in­ves­ti­gated the is­sue have been do­ing so for less than a decade, con­strained by mod­est bud­gets and small staffs. Much more re­search is needed to as­cer­tain the difficulty of im­prov­ing in­ver­te­brate lives. Even if large-scale in­ter­ven­tions are in­tractable, there may be low-hang­ing fruit that has been missed sim­ply be­cause the field is so ne­glected. Ad­di­tional in­ves­ti­ga­tion may yet re­veal that in­ver­te­brate welfare is an in­tractable cause area; how­ever, we are not yet in a po­si­tion to know this.

In this sec­tion we offer brief ex­am­ples to illus­trate the tractabil­ity of im­prov­ing in­ver­te­brate welfare along two timeframes. The first sub­sec­tion con­cerns the tractabil­ity of im­prov­ing in­ver­te­brate welfare now. The sec­ond sub­sec­tion con­cerns the tractabil­ity of im­prov­ing our chances to lo­cate cost-effec­tive in­ter­ven­tions in the medium-term. (Th­ese rep­re­sen­ta­tive ex­am­ple in­ter­ven­tions are not in­tended to be ex­haus­tive. For more in­for­ma­tion on our recom­mended di­rec­tions for fu­ture work, see our forth­com­ing “Next Steps” post.) Be­cause the in­ver­te­brate welfare move­ment is in its in­fancy and sup­port­ing the cause area at this point sim­ply means sup­port­ing ad­di­tional re­search, only the sec­ond sub­sec­tion is rele­vant to the im­por­tance-ne­glect­ed­ness-tractabil­ity frame­work. Nonethe­less, for those read­ers with the strong pre-the­o­retic be­lief that effec­tively helping in­ver­te­brates would be prac­ti­cally im­pos­si­ble, the first sub­sec­tion serves to show that this be­lief is prob­a­bly mis­taken.

Although the prospects of helping in­ver­te­brates at scale in the very near fu­ture are dim, there are sev­eral con­crete, tractable steps we can take now to bet­ter un­der­stand in­ver­te­brate sen­tience and bet­ter po­si­tion our­selves to help in­ver­te­brates in the fu­ture. The most im­por­tant in­ter­ven­tion at this stage is plau­si­bly rais­ing aware­ness about the cause area.[50] The ex­am­ples that fol­low may be most use­fully eval­u­ated ac­cord­ing to that crite­rion.

Helping In­ver­te­brates Now

Hu­mane Insecticides

Wild An­i­mal Ini­ti­a­tive is cur­rently con­duct­ing a re­search pro­ject to in­ves­ti­gate the fea­si­bil­ity of a hu­mane in­sec­ti­cide pro­gram. The goal of the pro­ject is to iden­tify in­sec­ti­cides that kill faster, less painfully, or both, while min­i­miz­ing down­stream ecolog­i­cal effects and im­pacts on non-tar­get species. Ac­cord­ing to their four month up­date, WAI has built a database of over 250 in­sec­ti­cides, doc­u­ment­ing their modes of ac­tion, pro­duc­ers, and other rele­vant in­for­ma­tion. They have also con­tacted out­side do­main spe­cial­ists to dis­cuss the vi­a­bil­ity of the pro­ject. The hope is that rel­a­tively small fi­nan­cial in­cen­tives could mo­ti­vate many users to adopt faster, less painful meth­ods for con­trol­ling in­sect pop­u­la­tions, thereby re­duc­ing a sig­nifi­cant amount of in­ver­te­brate suffer­ing.

Mesh to Re­duce By­catch in Sticky Traps

Sticky traps are ad­he­sive-coated cards with an al­lur­ing odor and/​or color de­ployed in large num­bers by pest man­agers to mon­i­tor for fly­ing in­sect pests in com­mer­cial or­chards. They pro­duce a sig­nifi­cant amount of by­catch, par­tic­u­larly lady­bugs and lacewings but also lizards and even some small birds. Re­search shows that sim­ple, in­ex­pen­sive mesh at­tached to the traps sig­nifi­cantly re­duces by­catch. Death by sticky trap is prob­a­bly es­pe­cially slow and un­pleas­ant, so re­duc­ing the amount of by­catch could plau­si­bly re­duce a sig­nifi­cant amount of in­ver­te­brate suffer­ing (and also a small amount of ver­te­brate suffer­ing).

Crus­tacean Live Boil Bans

It’s been ille­gal to boil crus­taceans al­ive in New Zealand since 1999. Switzer­land en­acted a similar ban in 2018. Crus­tacean Com­pas­sion is ac­tively cam­paign­ing for a similar ban (along with other pro­tec­tions) in the UK. If such a ban could be repli­cated across the whole of the EU, it would spare billions of an­i­mals from what ap­pears to be an ex­tremely painful death.

Cam­paigns Against Carmine

Carmine, also known as cochineal ex­tract, is a red dye widely used in yo­gurts, ice creams, so­das, cup­cakes, donuts, and lip­stick. It is made from the fe­male cochineal in­sect. Ac­cord­ing to Wikipe­dia, it takes roughly 80,000 in­sects to make a kilo­gram, and more than 220 tons of the stuff is pro­duced wor­ld­wide, yield­ing an es­ti­mate of roughly 16 billion in­sects kil­led per year.[51] The in­sects seem to be ei­ther boiled or baked al­ive. The gen­eral pub­lic ap­pears not to know that carmine is widely used in food prod­ucts and cos­met­ics. The gen­eral pub­lic also ap­pears to har­bor aver­sive at­ti­tudes to­wards both con­sum­ing ground-up bug paste and smear­ing it on faces. For those rea­sons, pub­lic aware­ness cam­paigns against carmine might be quite effec­tive in re­duc­ing its use. It has worked at least once in the past: on March 14, 2012, ThisDishIsVege­tar­ian.com re­ported that Star­bucks uses carmine in its straw­berry Frap­puc­ci­nos. An avalanche of nega­tive press fol­lowed. On April 19, a mere 36 days later, the chain an­nounced it would stop us­ing carmine in its food and bev­er­age prod­ucts.

Thwart­ing Entomophagy

En­to­mophagy refers to the prac­tice of eat­ing in­sects, es­pe­cially by hu­mans. Although peo­ple have been eat­ing in­sects for most of hu­man his­tory and many cul­tures con­tin­u­ing to eat in­sects, the prac­tice has not yet been adopted on a large scale in the in­dus­tri­al­ized world. If cer­tain fu­tur­ists are to be be­lieved, that is set to change. In­ter­est in en­to­mophagy ap­pears to be surg­ing. In 2013, the FAO re­leased a com­pre­hen­sive re­port on ed­ible in­sects. En­to­mophagy in­creas­ingly is mar­keted as a solu­tion to food in­se­cu­rity and a rem­edy to global warm­ing. (A quick Google search re­veals head­lines like “En­to­mophagy: How giv­ing up meat and eat­ing bugs can help save the planet.”) As of last year, when the rele­vant reg­u­la­tions came into force, ed­ible in­sects can be found in shops and su­per­mar­kets across Europe. How­ever, if in­sects are sen­tient, there are some pretty se­ri­ous welfare con­cerns at stake. So we seem to be at a key mo­ment in his­tory re­gard­ing this is­sue. Sus­tained pres­sure may be able to de­rail the en­to­mophagy move­ment now, thus spar­ing trillions of in­sects un­nec­es­sary suffer­ing. If the move­ment is al­lowed to gain even more mo­men­tum, it may be sig­nifi­cantly harder to kill later.

Helping In­ver­te­brates Later

Un­der­stand­ing In­ver­te­brate Life History

Be­fore we can hope to im­prove the lives of in­ver­te­brates, we must first know what those lives are like. Un­for­tu­nately, we know pre­cious lit­tle about the lives of most in­ver­te­brates. As noted above, per­va­sive tax­o­nomic bias in the life sci­ences en­sures that in­ver­te­brates are sys­tem­at­i­cally un­der­stud­ied. Even in the ab­sence of tax­o­nomic bias, there are many more in­ver­te­brate species than ver­te­brate species, and they are in many re­spects com­par­a­tively more difficult to study, so it’s no sur­prise we know so lit­tle. And among the in­ver­te­brates that have been thor­oughly stud­ied, hardly any have been stud­ied with their welfare in mind. Thank­fully, some EA or­ga­ni­za­tions are try­ing to close this knowl­edge gap. For in­stance, Re­think Pri­ori­ties re­cently re­leased a life his­tory re­port (writ­ten by a tenured pro­fes­sor of ecol­ogy) on her­bivorous in­sects. The re­port doc­u­ments var­i­ous data re­gard­ing lifes­pans, fe­cun­dity, mor­tal­ity rates, and mor­tal­ity causes. Th­ese data will help us bet­ter un­der­stand which in­ter­ven­tions might most effec­tively im­prove the welfare of her­bivorous in­sects. Similar re­ports should be com­mis­sioned for other large groups of in­ver­te­brates.

Pol­ling Public Attitudes

In the long-term im­prov­ing in­ver­te­brate welfare may well de­pend on ac­tively chang­ing at­ti­tudes to­wards in­ver­te­brates, es­pe­cially among effec­tive al­tru­ists, an­i­mal ac­tivists, aca­demics, and, ul­ti­mately, among leg­is­la­tors and lob­by­ists. But an ad­vo­cacy cam­paign can­not op­er­ate in an in­for­ma­tion vac­uum. One tan­gible and tractable next step is to poll pub­lic at­ti­tudes about in­ver­te­brates. This pol­ling should not only in­ves­ti­gate cur­rent at­ti­tudes to­wards in­ver­te­brates but also how malle­able those at­ti­tudes are. So, for ex­am­ple, an ex­per­i­ment might com­pare differ­ences in as­signed prob­a­bil­ity of con­scious­ness or moral weight in: i) peo­ple asked about a given taxon (e.g., lady­bugs), ii) peo­ple asked about “an an­i­mal” that has a list of ca­pac­i­ties, iii) peo­ple asked about lady­bugs and told they have cer­tain ca­pac­i­ties. With mod­est fund­ing, Re­think Pri­ori­ties is in a po­si­tion to con­duct such sur­veys.

Com­piling Ex­tant Scien­tific Re­search on More Species

Although we have already com­piled the ex­tant sci­en­tific re­search rele­vant to in­ver­te­brate sen­tience for 18 biolog­i­cal taxa, our efforts could have been more com­pre­hen­sive. There are at least a dozen more taxa that we would like to see added to this database. To strengthen analog­i­cal and similar­ity-driven ar­gu­ments, it would be helpful to have a more com­plete un­der­stand­ing of ver­te­brate sen­tience. Hence we would like to add a rep­re­sen­ta­tive am­phibian (class Am­phibia), a rep­re­sen­ta­tive rep­tile (class Rep­tilia), a rep­re­sen­ta­tive bony fish (su­per­class Oste­ichthyes), and a rep­re­sen­ta­tive car­tilag­i­nous fish (class Chon­drichthyes) to the database. On the in­ver­te­brate side, there are sev­eral ad­di­tions that could po­ten­tially be helpful. Phy­lum Mol­lusca con­tains coleoid cephalopods (rep­re­sented by fam­ily Oc­topo­di­dae on our table), and of all in­ver­te­brates, we are most con­fi­dent that these crea­tures are con­scious. But Mol­lusca also con­tains crea­tures like oys­ters and mus­sels, and there is a strong ini­tial case to be made that these an­i­mals are not con­scious. Thus, it would be good to in­ves­ti­gate class Bi­valvia (of which oys­ters and mus­sels are mem­bers) to bet­ter un­der­stand the dis­tri­bu­tion of sen­tience within Mol­lusca.[52] Stay­ing within the phy­lum, snails are con­sumed by hu­mans in many cul­tures[53] and have at­tracted some at­ten­tion as an edge case of con­scious­ness in philo­soph­i­cal cir­cles. A rep­re­sen­ta­tive from or­der Sty­lom­matophora would there­fore be use­ful. And if some in­ter­ven­tions are go­ing to tar­get hu­man con­sump­tion of in­ver­te­brates, more widely con­sumed in­ver­te­brates, like shrimp (sub­or­der Den­dro­branchi­ata), should also be added to the table. Other in­ver­te­brates ex­ploited by hu­mans in­clude silk­worms (genus Bom­byx), cochineal (genus Dacty­lopius), meal­worms (genus Tene­brio), house crick­ets (genus Acheta), and lac scales (fam­ily Ker­rii­dae). Be­fore cam­paign­ing against the ex­ploita­tion of these an­i­mals, we should have a firm grasp of the ev­i­dence that they are sen­tient. Fi­nally, as noted above, the Antarc­tic krill (genus Euphau­sia) is among the most nu­mer­ous in­di­vi­d­ual species on the planet. Any an­i­mal species num­ber­ing in the hun­dreds of trillions is worth un­der­stand­ing bet­ter.

Although much of the re­search we com­pile can be used by an­i­mal ad­vo­cates, they are not the only tar­get au­di­ence. Another goal of our pro­ject is to syn­the­size and dis­sem­i­nate in­for­ma­tion back to in­ver­te­brate re­searchers. A well-placed re­view ar­ti­cle or con­fer­ence pre­sen­ta­tion could spark dis­cus­sions that ul­ti­mately help mo­ti­vate re­searchers to work more di­rectly on this topic.

Bet­ter Pop­u­la­tion Estimates

If pos­si­ble, it could be ex­tremely use­ful to fund ad­di­tional re­search to bet­ter es­ti­mate in­ver­te­brate pop­u­la­tions. For ex­am­ple, the most widely cited global in­sect pop­u­la­tion es­ti­mate is nearly 60 years old. It’s an ex­trap­o­la­tion based on the num­ber of in­sects found on the Rotham­sted Farm Site in the United King­dom be­fore the wide­spread use of pes­ti­cides. Without more stud­ies (and, where fea­si­ble, a more rigor­ous method­ol­ogy), our es­ti­mates are likely to be off, in one di­rec­tion or the other, by sev­eral or­ders of mag­ni­tude. There is an al­most in­com­pre­hen­si­ble differ­ence be­tween there be­ing 100 quadrillion in­sects and there be­ing 100 quin­til­lion in­sects.

New Scien­tific Research

Aca­demic out­reach is likely to be a high-value ac­tivity in the near-term. Ad­di­tional sci­en­tific re­search will help us bet­ter un­der­stand in­ver­te­brate sen­tience. For in­stance, the effects of anal­gesics (pain-kil­ling drugs), anx­iolyt­ics (anti-anx­iety drugs), and var­i­ous recre­ational drugs have been well-doc­u­mented in many in­ver­te­brates. How­ever, it’s difficult to judge whether the be­hav­ioral changes these drugs in­duce are merely a product of phys­iolog­i­cal re­sponses or in­stead re­flect a change in the valence of ex­pe­rience. Self-ad­minis­tra­tion stud­ies can help us tease the two apart. So, for ex­am­ple, if a pur­port­edly stressed an­i­mal con­sis­tently fa­vored a food source laced with an anx­iolytic, that would be mild ev­i­dence that the stress causes a nega­tively valenced emo­tional state for which the an­i­mal seeks re­lief. To our knowl­edge, there has only been a sin­gle anal­gesic self-ad­minis­tra­tion study on an in­ver­te­brate species and no anx­iolytic or an­tide­pres­sant self-ad­minis­tra­tion stud­ies on in­ver­te­brate species.

Pre­limi­nary Conclusion

Our ap­proach to in­ver­te­brate sen­tience and in­ver­te­brate welfare is es­sen­tially com­par­a­tive. The effec­tive an­i­mal ac­tivism com­mu­nity already de­votes con­sid­er­able re­sources to helping mam­mals, birds, and (to a lesser ex­tent) fish.[54] An­i­mal ad­vo­cates think that mam­mals, birds, and fish are sen­tient on the ba­sis of well-es­tab­lished be­hav­ioral and neu­ro­biolog­i­cal facts. There is no rea­son in prin­ci­ple why this ap­proach can­not be ex­tended to in­ver­te­brates. Although the un­der­ly­ing sci­ence is more un­cer­tain, the same sort of be­hav­ioral and neu­ro­biolog­i­cal ev­i­dence that leads us to at­tribute con­scious states to mam­mals, birds, and fish is also available for some in­ver­te­brates, no­tably cephalopods and many arthro­pods. So if one thinks mam­mals, birds, and fish are con­scious, one should take the idea of in­ver­te­brate con­scious­ness se­ri­ously. More­over, there are far more arthro­pods (to take just one in­ver­te­brate phy­lum) than there are mam­mals, birds, and fish. So even if the case for arthro­pod con­scious­ness is weaker than the case for mam­mal, bird, and fish con­scious­ness, the ex­pected value of helping arthro­pods might be higher—po­ten­tially much higher—than the ex­pected value of helping mam­mals, birds, and fish.

Of course, tremen­dous un­cer­tainty re­mains. As our sci­en­tific and philo­soph­i­cal un­der­stand­ing of con­scious­ness con­tinues to im­prove, we may dis­cover defini­tive rea­sons to think con­scious­ness is re­stricted to ver­te­brates. Even if we think that in­ver­te­brates are con­scious, we might come to jus­tifi­ably be­lieve that the moral value of their ex­pe­riences is neg­ligible. And even if in­ver­te­brates do have morally valuable ex­pe­riences, it might turn out that there is no cost-effec­tive way to help them. But we aren’t yet in a po­si­tion to know any of these things. We don’t know enough about con­scious­ness to be cer­tain that arthro­pods and cephalopods aren’t con­scious. We don’t know enough about nor­ma­tive ethics to be cer­tain we don’t have moral obli­ga­tions to these crea­tures. We don’t know enough about the tractabil­ity of im­prov­ing in­ver­te­brate welfare to be cer­tain we can’t help these an­i­mals. And be­cause there are a truly mind-bog­gling num­ber of in­ver­te­brates, the cause area has the po­ten­tial to be ex­tremely high-value. Thus, we think that at this stage in­ver­te­brate welfare is a cause area that ought to be pri­ori­tized.

Credits

This es­say is a pro­ject of Re­think Pri­ori­ties. It was writ­ten by Ja­son Schukraft. Thanks to Mar­cus A. Davis, Jamie Git­tins, Michelle Gra­ham, Kieran Greig, Sam Fox Krauss, Peter Hur­ford, David Moss, Abra­ham Rowe, Ja­cob Sch­miess, Gavin Tay­lor, Daniela R. Wald­horn, and Rachael Woodard for helpful feed­back. If you like our work, please con­sider sub­scribing to our newslet­ter. You can see all our work to date here.

Works Cited

Ab­bott, K. R., & Dukas, R. (2009). Honey­bees con­sider flower dan­ger in their wag­gle dance. An­i­mal Be­havi­our, 78(3), 633-635.

Atk­in­son, A., Siegel, V., Pakho­mov, E. A., Jes­sopp, M. J., & Loeb, V. (2009). A re-ap­praisal of the to­tal bio­mass and an­nual pro­duc­tion of Antarc­tic krill. Deep Sea Re­search Part I: Oceano­graphic Re­search Papers, 56(5), 727-740.

Baars, B. J. (1988). A Cog­ni­tive The­ory of Con­scious­ness. Cam­bridge: Cam­bridge Univer­sity Press.

Bar-On, Y. M., Phillips, R., & Milo, R. (2018). The bio­mass dis­tri­bu­tion on Earth. Pro­ceed­ings of the Na­tional Academy of Sciences, 115(25), 6506-6511.

Bate­son, M., De­sire, S., Gart­side, S. E., & Wright, G. A. (2011). Agi­tated hon­ey­bees ex­hibit pes­simistic cog­ni­tive bi­ases. Cur­rent biol­ogy, 21(12), 1070-1073.

Belzung, C., & Philip­pot, P. (2007). Anx­iety from a phy­lo­ge­netic per­spec­tive: is there a qual­i­ta­tive differ­ence be­tween hu­man and an­i­mal anx­iety?. Neu­ral plas­tic­ity, 2007.

Bos, N., Guer­ri­eri, F. J., & d’Et­torre, P. (2010). Sig­nifi­cance of chem­i­cal recog­ni­tion cues is con­text de­pen­dent in ants. An­i­mal Be­havi­our, 80(5), 839-844.

Boulay, R., Quage­beur, M., Godz­in­ska, E. J., & Lenoir, A. (1999). So­cial iso­la­tion in ants: ev­i­dence of its im­pact on sur­vivor­ship and be­hav­ior in Cam­pono­tus fel­lah (Hy­menoptera: Formi­ci­dae). So­cio­biol­ogy, 33(2), 111-124.

Breed, M. D. (1983). Cor­re­la­tions be­tween ag­gres­sive­ness and cor­pora al­lata vol­ume, so­cial iso­la­tion, age and dietary pro­tein in worker hon­ey­bees. In­sectes So­ci­aux, 30(4), 482-495.

Brown, C., Gar­wood, M. P., & Willi­am­son, J. E. (2012). It pays to cheat: tac­ti­cal de­cep­tion in a cephalo­pod so­cial sig­nal­ling sys­tem. Biol­ogy let­ters, 8(5), 729-732.

Chap­man, A. D., & Chap­man, A. D. (2009). Num­bers of liv­ing species in Aus­tralia and the world.

Cheng, K., Peña, J., Porter, M. A., & Ir­win, J. D. (2002). Self-con­trol in hon­ey­bees. Psy­cho­nomic bul­letin & re­view, 9(2), 259-263.

Chit­tka, L., & Niven, J. (2009). Are big­ger brains bet­ter?. Cur­rent Biol­ogy, 19(21), R995-R1008.

Cza­czkes, T. J., & Heinze, J. (2015). Ants ad­just their pheromone de­po­si­tion to a chang­ing en­vi­ron­ment and their prob­a­bil­ity of mak­ing er­rors. Pro­ceed­ings of the Royal So­ciety B: Biolog­i­cal Sciences, 282(1810), 20150679.

DeGrazia, D. (2008). Mo­ral sta­tus as a mat­ter of de­gree?. The South­ern Jour­nal of Philos­o­phy, 46(2), 181-198.

Finn, J. K., Tre­genza, T., & Nor­man, M. D. (2009). Defen­sive tool use in a co­conut-car­ry­ing oc­to­pus. Cur­rent Biol­ogy, 19(23), R1069-R1070.

Fos­sat, P., Bac­qué-Cazenave, J., De Deur­waerdère, P., Delbecque, J. P., & Cat­taert, D. (2014). Anx­iety-like be­hav­ior in crayfish is con­trol­led by sero­tonin. Science, 344(6189), 1293-1297.

Gut­nick, T., Byrne, R. A., Hochner, B., & Kuba, M. (2011). Oc­to­pus vul­garis uses vi­sual in­for­ma­tion to de­ter­mine the lo­ca­tion of its arm. Cur­rent biol­ogy, 21(6), 460-462.

Healy, K., McNally, L., Rux­ton, G. D., Cooper, N., & Jack­son, A. L. (2013). Metabolic rate and body size are linked with per­cep­tion of tem­po­ral in­for­ma­tion. An­i­mal Be­havi­our, 86(4), 685-696.

Hochner, B., Shom­rat, T., & Fiorito, G. (2006). The oc­to­pus: a model for a com­par­a­tive anal­y­sis of the evolu­tion of learn­ing and mem­ory mechanisms. The Biolog­i­cal Bul­letin, 210(3), 308-317.

Kel­lert, S. R. (1993). Values and per­cep­tions of in­ver­te­brates. Con­ser­va­tion biol­ogy, 7(4), 845-855.

Loukola, O. J., Perry, C. J., Coscos, L., & Chit­tka, L. (2017). Bum­ble­bees show cog­ni­tive flex­i­bil­ity by im­prov­ing on an ob­served com­plex be­hav­ior. Science, 355(6327), 833-836.

Maák, I., Lőrinczi, G., Le Quin­quis, P., Mó­dra, G., Bovet, D., Call, J., & d’Et­torre, P. (2017). Tool se­lec­tion dur­ing for­ag­ing in two species of fun­nel ants. An­i­mal be­havi­our, 123, 207-216.

Magee, B., & El­wood, R. W. (2013). Shock avoidance by dis­crim­i­na­tion learn­ing in the shore crab (Carcinus mae­nas) is con­sis­tent with a key crite­rion for pain. Jour­nal of Ex­per­i­men­tal Biol­ogy, 216(3), 353-358.

Magee, B., & El­wood, R. W. (2016). Trade-offs be­tween preda­tor avoidance and elec­tric shock avoidance in her­mit crabs demon­strate a non-re­flex­ive re­sponse to nox­ious stim­uli con­sis­tent with pre­dic­tion of pain. Be­havi­oural pro­cesses, 130, 31-35.

Mather, J. A. (2008). Cephalo­pod con­scious­ness: be­havi­oural ev­i­dence. Con­scious­ness and cog­ni­tion, 17(1), 37-48.

Mota, T., Giurfa, M., & San­doz, J. C. (2011). Color mod­u­lates ol­fac­tory learn­ing in hon­ey­bees by an oc­ca­sion-set­ting mechanism. Learn­ing & Me­mory, 18(3), 144-155.

Öh­man, A. (2000). Fear and Anx­iety: Evolu­tion­ary, Cog­ni­tive, and Clini­cal per­spec­tives. in M. Lewis & J.M. Hav­iland-Jones (eds.). Hand­book of Emo­tions. pp. 573–93. New York: The Guilford Press.

Oizumi, M., Alban­takis, L., & Tononi, G. (2014). From the phe­nomenol­ogy to the mechanisms of con­scious­ness: in­te­grated in­for­ma­tion the­ory 3.0. PLoS com­pu­ta­tional biol­ogy, 10(5), e1003588.

Perry, C. J., Bar­ron, A. B., & Cheng, K. (2013). In­ver­te­brate learn­ing and cog­ni­tion: re­lat­ing phe­nom­ena to neu­ral sub­strate. Wiley In­ter­dis­ci­plinary Re­views: Cog­ni­tive Science, 4(5), 561-582.

Perry, C. J., & Bar­ron, A. B. (2013). Honey bees se­lec­tively avoid difficult choices. Pro­ceed­ings of the Na­tional Academy of Sciences, 110(47), 19155-19159.

Pi­queret, B., San­doz, J. C., & d’Et­torre, P. (2019). Ants learn fast and do not for­get: as­so­ci­a­tive ol­fac­tory learn­ing, mem­ory and ex­tinc­tion in Formica fusca. Royal So­ciety Open Science, 6(6), 190778.

Plowes, N. (2010). An in­tro­duc­tion to eu­so­cial­ity. Na­ture Ed­u­ca­tion Knowl­edge, 3(10), 7.

Rod­house, P. G., & Nig­mat­ul­lin, C. M. (1996). Role as con­sumers. Philo­soph­i­cal Trans­ac­tions of the Royal So­ciety of Lon­don. Series B: Biolog­i­cal Sciences, 351(1343), 1003-1022.

Rosen­thal, M. F., Gertler, M., Hamil­ton, A. D., Prasad, S., & An­drade, M. C. (2017). Tax­o­nomic bias in an­i­mal be­havi­our pub­li­ca­tions. An­i­mal Be­havi­our, 127, 83-89.

Rowe, A. (2018). Should Scien­tific Re­search In­volv­ing De­ca­pod Crus­taceans Re­quire Eth­i­cal Re­view?. Jour­nal of Agri­cul­tural and En­vi­ron­men­tal Ethics, 31(5), 625-634.

Schultz, T. R. (2000). In search of ant an­ces­tors. Pro­ceed­ings of the Na­tional Academy of Sciences, 97(26), 14028-14029.

Smith, E. S. J., & Lewin, G. R. (2009). No­ci­cep­tors: a phy­lo­ge­netic view. Jour­nal of Com­par­a­tive Phys­iol­ogy A, 195(12), 1089-1106.

Sned­don, L. U. (2017). Com­par­a­tive phys­iol­ogy of no­ci­cep­tion and pain. Phys­iol­ogy, 33(1), 63-73.

Stroeymeyt, N., Giurfa, M., & Franks, N. R. (2017). In­for­ma­tion cer­tainty de­ter­mines so­cial and pri­vate in­for­ma­tion use in ants. Scien­tific re­ports, 7, 43607.

Su­na­mura, E., Es­padaler, X., Sakamoto, H., Suzuki, S., Ter­ayama, M., & Tat­suki, S. (2009). In­ter­con­ti­nen­tal union of Ar­gen­tine ants: be­hav­ioral re­la­tion­ships among in­tro­duced pop­u­la­tions in Europe, North Amer­ica, and Asia. In­sectes So­ci­aux, 56(2), 143-147.

Thomas, A., & MacDon­ald, C. (2016). In­ves­ti­gat­ing body pat­tern­ing in aquar­ium-raised flam­boy­ant cut­tlefish (Me­tasepia pfefferi). PeerJ, 4, e2035.

Tib­betts, E. A., Agudelo, J., Pan­dit, S., & Rio­jas, J. (2019). Tran­si­tive in­fer­ence in Polistes pa­per wasps. Biol­ogy let­ters, 15(5), 20190015.

Tib­betts, E. A., Des­jardins, E., Kou, N., & Wel­l­man, L. (2019). So­cial iso­la­tion pre­vents the de­vel­op­ment of in­di­vi­d­ual face recog­ni­tion in pa­per wasps. An­i­mal Be­havi­our, 152, 71-77.

Troudet, J., Grand­co­las, P., Blin, A., Vignes-Lebbe, R., & Le­gen­dre, F. (2017). Tax­o­nomic bias in bio­di­ver­sity data and so­cietal prefer­ences. Scien­tific Re­ports, 7(1), 9132.

Wells, M. J. (1964). De­tour ex­per­i­ments with oc­to­puses. Jour­nal of Ex­per­i­men­tal Biol­ogy, 41(3), 621-642.

Willi­ams, C. B. (1960). The range and pat­tern of in­sect abun­dance. The Amer­i­can Nat­u­ral­ist, 94(875), 137-151.

Young, R. E., Vec­chione, M., & Dono­van, D. T. (1998). The evolu­tion of coleoid cephalopods and their pre­sent bio­di­ver­sity and ecol­ogy. Afri­can Jour­nal of Marine Science, 20.

Notes


  1. Ver­te­brates con­sti­tute a sub­phy­lum in the phy­lum Chor­data. Cladis­ti­cally, it would be more pre­cise to speak of ‘chor­dates’ and ‘non-chor­dates.’ In us­ing the terms ‘ver­te­brates’ and ‘in­ver­te­brates’ we defer to com­mon us­age. How­ever the num­ber of in­ver­te­brates in the phy­lum Chor­data is triv­ial com­pared to the num­ber of in­ver­te­brates out­side Chor­data, so com­mon us­age is not wholly in­ac­cu­rate. ↩︎

  2. We use the terms ‘sen­tience,’ ‘phe­nom­e­nal con­scious­ness,’ and ‘sub­jec­tive ex­pe­rience’ in­ter­change­ably. An or­ganism is sen­tient just in case there is some­thing it is like to be that or­ganism. ‘Valenced ex­pe­rience’ de­notes a proper sub­set of con­scious ex­pe­rience in which ex­pe­riences take on a pos­i­tive or nega­tive af­fect. All crea­tures with the ca­pac­ity for valenced ex­pe­rience are nec­es­sar­ily sen­tient, but not all sen­tient crea­tures nec­es­sar­ily have the ca­pac­ity for valenced ex­pe­rience. ↩︎

  3. ‘In­ver­te­brate sen­tience’ is similarly mis­lead­ing for the same rea­son. Ad­di­tion­ally, some species of in­ver­te­brates are much more stud­ied than oth­ers. Thus, given the cur­rent sci­en­tific ev­i­dence, we have differ­ent de­grees of con­fi­dence about which of them are sen­tient. It isn’t ap­pro­pri­ate to gen­er­al­ize based on ev­i­dence that is only valid for spe­cific groups of in­ver­te­brates. ↩︎

  4. Some of the in­ter­ven­tions would tar­get in­ver­te­brates sub­jected to hu­man ex­ploita­tion, while other in­ter­ven­tions might tar­get in­ver­te­brates suffer­ing due to nat­u­ral causes. ↩︎

  5. Be­cause in­ver­te­brate welfare is not yet a ma­ture field, it’s im­pos­si­ble to know in ad­vance which in­ter­ven­tions will be high-value. Th­ese ex­am­ples are used for illus­tra­tive pur­poses only. ↩︎

  6. See Table S1 in the Sup­ple­men­tary In­for­ma­tion Ap­pendix of Bar-On, Y. M., Phillips, R., & Milo, R. (2018). The bio­mass dis­tri­bu­tion on Earth. Pro­ceed­ings of the Na­tional Academy of Sciences, 115(25), 6506-6511. ↩︎

  7. Axel Ross­berg of Queen Mary’s Univer­sity es­ti­mates that at least 600 quin­til­lion ne­ma­todes are born ev­ery day. ↩︎

  8. Willi­ams, C. B. (1960). The range and pat­tern of in­sect abun­dance. The Amer­i­can Nat­u­ral­ist, 94(875), 137-151. This study is old, and its method­ol­ogy fairly sim­plis­tic. Nonethe­less, it is the most com­monly cited global in­sect pop­u­la­tion es­ti­mate in the liter­a­ture. Given the way our un­der­stand­ing of tax­on­omy has im­proved since this study was con­ducted, this figure might bet­ter rep­re­sent the to­tal num­ber of ter­res­trial arthro­pods. ↩︎

  9. Atk­in­son, A., Siegel, V., Pakho­mov, E. A., Jes­sopp, M. J., & Loeb, V. (2009). A re-ap­praisal of the to­tal bio­mass and an­nual pro­duc­tion of Antarc­tic krill. Deep Sea Re­search Part I: Oceano­graphic Re­search Papers, 56(5), 727-740. This figure ap­pears to be for post­lar­val krill. If most krill die young, this figure could be a big un­der­es­ti­mate. ↩︎

  10. The num­ber of wild-caught crus­taceans is po­ten­tially even higher. Ac­cord­ing to FAO data, more than six mil­lion met­ric tons of crus­taceans were cap­tured in 2017. ↩︎

  11. See page 44 of the ap­pendix of Bar-On, Y. M., Phillips, R., & Milo, R. (2018). The bio­mass dis­tri­bu­tion on Earth. Pro­ceed­ings of the Na­tional Academy of Sciences, 115(25), 6506-6511. ↩︎

  12. See Figure 1 in Bar-On, Y. M., Phillips, R., & Milo, R. (2018). The bio­mass dis­tri­bu­tion on Earth. Pro­ceed­ings of the Na­tional Academy of Sciences, 115(25), 6506-6511. ↩︎

  13. In this sec­tion I fo­cus solely on healthy adults for all species. This sim­plifi­ca­tion ig­nores the moral sig­nifi­cance of the po­ten­tial for de­vel­op­ing morally sig­nifi­cant prop­er­ties. It also ig­nores the moral sig­nifi­cance (if there is any) of be­long­ing to a group whose av­er­age or nor­mal mem­bers have a cer­tain moral sta­tus. ↩︎

  14. Only dream­less sleep lacks a phe­nomenol­ogy so only dream­less sleep counts as un­con­scious ac­cord­ing to our defi­ni­tion. ↩︎

  15. See, in­ter alia, Baars, B. J. (1988). A Cog­ni­tive The­ory of Con­scious­ness. Cam­bridge: Cam­bridge Univer­sity Press. ↩︎

  16. For ex­am­ple, honey bees are ca­pa­ble of mul­ti­modal as­so­ci­a­tive learn­ing. They can rec­og­nize that when one color is pre­sented to them, odor A pre­dicts a su­crose re­ward and odor B does not, but when a differ­ent color is pre­sented, odor B pre­dicts a su­crose re­ward and odor A does not. This find­ing re­flects the fact that when for­ag­ing, a sin­gle modal­ity by it­self can’t parse benefi­cial flower species from non-benefi­cial species. Bees rely on a com­bi­na­tion of color, shape, and odor to dis­t­in­guish good flow­ers from use­less ones. Mota, T., Giurfa, M., & San­doz, J. C. (2011). Color mod­u­lates ol­fac­tory learn­ing in hon­ey­bees by an oc­ca­sion-set­ting mechanism. Learn­ing & Me­mory, 18(3), 144-155. ↩︎

  17. Alter­na­tively, it might be the the statis­ti­cal reg­u­lar­ity of the pat­tern rather than the phe­nom­e­nal in­ten­sity of the pat­tern that would be as­sisted by cog­ni­tive so­phis­ti­ca­tion. Thanks to Gavin Tay­lor for this point. ↩︎

  18. Even more so than the rest of this post, the fore­go­ing para­graph is highly spec­u­la­tive. The aim of the ar­gu­ment therein is sim­ply to push back against the in­tu­ition that phe­nom­e­nal in­ten­sity de­clines as cog­ni­tive so­phis­ti­ca­tion de­clines. ↩︎

  19. DeGrazia, D. (2008). Mo­ral sta­tus as a mat­ter of de­gree?. The South­ern Jour­nal of Philos­o­phy, 46(2), 181-198. He adds, “Thus per­sons have the high­est moral sta­tus, Great Apes and dolphins a bit less, elephants and mon­keys some­what less than apes and dolphins, mid­dling mam­mals still less, ro­dents less, and so on down through the phy­lo­ge­netic scale (to the ex­tent that it tracks com­plex­ity of the rele­vant sorts) from birds to rep­tiles to am­phibi­ans to any other an­i­mals who are sen­tient.” ↩︎

  20. DeGrazia 2008: 193. ↩︎

  21. So, for in­stance, the scale of far-off suffer­ing cer­tainly gives us a rea­son to speed up re­search into in­ter­stel­lar travel. ↩︎

  22. There are, con­ser­va­tively, 10 quin­til­lion arthro­pods, give or take an or­der of mag­ni­tude. Say you only have a 1% cre­dence that arthro­pods have morally rele­vant ex­pe­riences. That knocks you down to 100 quadrillion ex­pected arthro­pods. Say you think moral weight is de­ter­mined by neu­ron count. Take a con­ser­va­tive av­er­age neu­ron count for arthro­pods (100,000) and use 100 mil­lion (putting you roughly in the range of ro­dents) as an ex­am­ple of a morally valuable ver­te­brate. That means, even with 1% cre­dence and ad­just­ing down­ward for moral weight, arthro­pods are worth roughly 100 trillion morally valuable ver­te­brates. (For com­par­i­son, there are prob­a­bly no more than a trillion birds.) ↩︎

  23. Other in­ter­ven­tion tar­gets are less am­bigu­ous. For in­stance, we can say with rea­son­able cer­tainty that lob­sters should not be boiled al­ive. ↩︎

  24. This is not to say that there aren’t neu­ro­scien­tists, ecol­o­gists, ethol­o­gists and the like do­ing re­search that is rele­vant to in­ver­te­brate sen­tience and welfare. (See our In­ver­te­brate Sen­tience Table for a col­la­tion of such knowl­edge.) The point is that these sci­en­tists aren’t fram­ing their re­search in terms of figur­ing out whether in­ver­te­brates are sen­tient and if so how to im­prove their welfare. ↩︎

  25. On the aca­demic side of things, there is po­ten­tially more abil­ity to ab­sorb fund­ing, if we can get the right peo­ple on board. The in­fras­truc­ture for sci­en­tific re­search on ques­tions rele­vant to in­ver­te­brate sen­tience is already largely in place. To uti­lize this in­fras­truc­ture we need to build in­ter­est in the topic, iden­tify promis­ing pro­jects, and co­or­di­nate the rele­vant re­searchers. ↩︎

  26. It’s im­por­tant to note that one can pre­fer an ex­pla­na­tion with­out fully be­liev­ing the ex­pla­na­tion. If there are nu­mer­ous plau­si­ble ex­pla­na­tions, the best ex­pla­na­tion might only war­rant a cre­dence of 20%. For ex­am­ple, it’s con­sis­tent to have a fairly low cre­dence in the claim that in­ver­te­brates feel pain and yet think that that ex­pla­na­tion of their be­hav­ior is more likely than any other ex­pla­na­tion of their be­hav­ior. ↩︎

  27. Ev­i­dence for panpsy­chism would triv­ially qual­ify as ev­i­dence for in­ver­te­brate sen­tience. Similarly, ev­i­dence for the view that all an­i­mals or all liv­ing things are con­scious would also qual­ify. ↩︎

  28. Smith, E. S. J., & Lewin, G. R. (2009). No­ci­cep­tors: a phy­lo­ge­netic view. Jour­nal of Com­par­a­tive Phys­iol­ogy A, 195(12), 1089-1106. No­ci­cep­tors, the spe­cial­ized periph­eral sen­sory cells that de­tect po­ten­tially harm­ful stim­uli, have been iden­ti­fied in fruit flies, sea slugs, and the ne­ma­tode C. el­e­gans. They are prob­a­bly ubiquitous. See Sned­don, L. U. (2017). Com­par­a­tive phys­iol­ogy of no­ci­cep­tion and pain. Phys­iol­ogy, 33(1), 63-73. ↩︎

  29. Young, R. E., Vec­chione, M., & Dono­van, D. T. (1998). The evolu­tion of coleoid cephalopods and their pre­sent bio­di­ver­sity and ecol­ogy. Afri­can Jour­nal of Marine Science, 20. ↩︎

  30. Hochner, B., Shom­rat, T., & Fiorito, G. (2006). The oc­to­pus: a model for a com­par­a­tive anal­y­sis of the evolu­tion of learn­ing and mem­ory mechanisms. The Biolog­i­cal Bul­letin, 210(3), 308-317. ↩︎

  31. Finn, J. K., Tre­genza, T., & Nor­man, M. D. (2009). Defen­sive tool use in a co­conut-car­ry­ing oc­to­pus. Cur­rent Biol­ogy, 19(23), R1069-R1070. Im­por­tantly, the only known source of these clean and lightweight shells is the coastal hu­man com­mu­ni­ties, and thus the oc­to­puses have not in­ter­acted with these items on an evolu­tion­ary timescale. ↩︎

  32. Wells, M. J. (1964). De­tour ex­per­i­ments with oc­to­puses. Jour­nal of Ex­per­i­men­tal Biol­ogy, 41(3), 621-642. See also Gut­nick, T., Byrne, R. A., Hochner, B., & Kuba, M. (2011). Oc­to­pus vul­garis uses vi­sual in­for­ma­tion to de­ter­mine the lo­ca­tion of its arm. Cur­rent biol­ogy, 21(6), 460-462. ↩︎

  33. Thomas, A., & MacDon­ald, C. (2016). In­ves­ti­gat­ing body pat­tern­ing in aquar­ium-raised flam­boy­ant cut­tlefish (Me­tasepia pfefferi). PeerJ, 4, e2035. ↩︎

  34. Euro­pean Food Safety Author­ity (EFSA). (2005). Opinion of the Scien­tific Panel on An­i­mal Health and Welfare (AHAW) on a re­quest from the Com­mis­sion re­lated to the as­pects of the biol­ogy and welfare of an­i­mals used for ex­per­i­men­tal and other sci­en­tific pur­poses. EFSA Jour­nal, 3(12), 292. ↩︎

  35. Rowe, A. (2018). Should Scien­tific Re­search In­volv­ing De­ca­pod Crus­taceans Re­quire Eth­i­cal Re­view?. Jour­nal of Agri­cul­tural and En­vi­ron­men­tal Ethics, 31(5), 625-634. ↩︎

  36. Ac­cord­ing to FAO data, ap­prox­i­mately 90% of wild-caught crus­taceans in 2017 were de­capods. ↩︎

  37. Fos­sat, P., Bac­qué-Cazenave, J., De Deur­waerdère, P., Delbecque, J. P., & Cat­taert, D. (2014). Anx­iety-like be­hav­ior in crayfish is con­trol­led by sero­tonin. Science, 344(6189), 1293-1297. Note that the pop­u­lar in­tro­duc­tion to the ar­ti­cle mis­tak­enly states that the crayfish were afraid of the dark, not the light. A cor­rected ti­tle for the pop­u­lar in­tro­duc­tion is available here. ↩︎

  38. Separately, the in­jec­tion of sero­tonin in un­shocked crayfish in­duced light-aver­sion be­hav­ior that was also elimi­nated by chlor­diazepox­ide. In hu­mans, ele­vated lev­els of sero­tonin are as­so­ci­ated with anx­iety. ↩︎

  39. Öh­man, A. (2000). Fear and Anx­iety: Evolu­tion­ary, Cog­ni­tive, and Clini­cal per­spec­tives. in M. Lewis & J.M. Hav­iland-Jones (eds.). Hand­book of Emo­tions. pp. 573–93. New York: The Guilford Press. ↩︎

  40. Belzung, C., & Philip­pot, P. (2007). Anx­iety from a phy­lo­ge­netic per­spec­tive: is there a qual­i­ta­tive differ­ence be­tween hu­man and an­i­mal anx­iety?. Neu­ral plas­tic­ity, 2007. ↩︎

  41. Plowes, N. (2010). An in­tro­duc­tion to eu­so­cial­ity. Na­ture Ed­u­ca­tion Knowl­edge, 3(10), 7. ↩︎

  42. Loukola, O. J., Perry, C. J., Coscos, L., & Chit­tka, L. (2017). Bum­ble­bees show cog­ni­tive flex­i­bil­ity by im­prov­ing on an ob­served com­plex be­hav­ior. Science, 355(6327), 833-836. See here for an in­ex­pli­ca­bly adorable demon­stra­tion. ↩︎

  43. Bos, N., Guer­ri­eri, F. J., & d’Et­torre, P. (2010). Sig­nifi­cance of chem­i­cal recog­ni­tion cues is con­text de­pen­dent in ants. An­i­mal Be­havi­our, 80(5), 839-844. ↩︎

  44. Perry, C. J., & Bar­ron, A. B. (2013). Honey bees se­lec­tively avoid difficult choices. Pro­ceed­ings of the Na­tional Academy of Sciences, 110(47), 19155-19159. ↩︎

  45. Stroeymeyt, N., Giurfa, M., & Franks, N. R. (2017). In­for­ma­tion cer­tainty de­ter­mines so­cial and pri­vate in­for­ma­tion use in ants. Scien­tific re­ports, 7, 43607. ↩︎

  46. Cza­czkes, T. J., & Heinze, J. (2015). Ants ad­just their pheromone de­po­si­tion to a chang­ing en­vi­ron­ment and their prob­a­bil­ity of mak­ing er­rors. Pro­ceed­ings of the Royal So­ciety B: Biolog­i­cal Sciences, 282(1810), 20150679. It should be noted that the au­thors are un­cer­tain about what their find­ings rep­re­sent. They write that “it’s hard to be­lieve that such tiny-brained an­i­mals are ca­pa­ble of such an ad­vanced cog­ni­tive feat” and “one could con­ceive of sev­eral al­ter­na­tive ex­pla­na­tions for our find­ings, which do not in­voke metacog­ni­tion.” At the same time, they ar­gue that their find­ings, “alongside similar re­sults from hon­ey­bees (Perry & Bar­ron, 2013), are sug­ges­tive of metacog­ni­tive abil­ities in so­cial in­sects.” ↩︎

  47. Re­think Pri­ori­ties ac­counts for roughly $70,000 of this figure. Wild An­i­mal Ini­ti­a­tive pro­jects $353,710 in 2019 ex­penses, of which roughly $85,000 will go to­wards in­ver­te­brate spe­cific re­search and $50,000 to $70,000 will go to­wards things po­ten­tially rele­vant to fu­ture in­ver­te­brate re­search. ↩︎

  48. As an­other com­par­i­son, in the 2019 first quar­ter grant round, CEA’s An­i­mal Welfare Fund dis­bursed $445,000, CEA’s Meta Fund dis­bursed $512,000, CEA’s Long-Term Fu­ture Fund dis­bursed $923,150, and CEA’s Global Health and Devel­op­ment Fund dis­bursed $1,705,000. ↩︎

  49. There’s also a smat­ter­ing of philoso­phers in­ves­ti­gat­ing in­ver­te­brate sen­tience. Colin Klein at ANU co-au­thored the Bar­ron pa­per ar­gu­ing that in­sects have the ca­pac­ity for sub­jec­tive ex­pe­rience. Michael Tye at UT Austin ar­gues that we are li­censed to pre­fer ex­pla­na­tions of in­sect and crus­tacean be­hav­ior that in­voke phe­nom­e­nal states to ex­pla­na­tions that do not. Peter God­frey-Smith at the Univer­sity of Syd­ney has long main­tained that cephalopods are con­scious. In most cases, philo­soph­i­cal in­ves­ti­ga­tions into in­ver­te­brate sen­tience de­pend heav­ily on em­piri­cal work con­ducted by re­searchers of the sort cited in the main text. ↩︎

  50. Of course, it’s im­por­tant to pro­ceed cau­tiously with any out­reach cam­paigns. A poorly planned or ex­e­cuted cam­paign could back­fire and lead not only to re­duced sup­port for in­ver­te­brate welfare but re­duced sup­port for effec­tive al­tru­ism as a whole. There is also the worry that rush­ing into an ad­vo­cacy cam­paign could cre­ate hard-to-re­verse lock-in effects. If the ini­tial mes­sage is sub­op­ti­mal, these lock-in effects could im­pose sub­stan­tial costs. ↩︎

  51. Brian To­masik es­ti­mates a much higher figure: 120 billion. ↩︎

  52. Not all bi­valves are as dull as oys­ters and mus­sels. Clams and scal­lops have eyes and move around a bit more. Thanks to Gavin Tay­lor for this clar­ifi­ca­tion. ↩︎

  53. Global snail pro­duc­tion amounted to 43,000 met­ric tons in 2016. ↩︎

  54. The vast ma­jor­ity of these re­sources go to helping farmed mam­mals, birds, and fish. How­ever, the wild an­i­mal welfare crowd also tar­gets these groups of an­i­mals. ↩︎