The scale of direct human impact on invertebrates
Summary
Currently, estimates of the number of invertebrates used or killed by humans are very poor.
Summing the rigorous estimates that exist, at least 7.2 trillion to 26 trillion invertebrates annually are killed directly by humans, and 18 trillion to 40 trillion are used but not killed annually.
I outline some of the largest invertebrate industries, and estimate the total number of invertebrates used or killed by humans.
I don’t look at indirect deaths, such as invertebrates impacted by climate change.
In total, not including nematodes, I believe between 100 trillion and 10 quadrillion invertebrates are directly killed or used annually by humans.
The majority of this impact is caused by the application of agricultural pesticides.
Introduction
The effective altruist case for working on farmed animals has historically focused on both the sheer number of farmed animals, and the relative neglectedness of farmed animals. Groups have argued that due to the vast number of farmed animals, more funding ought to be directed to reducing their suffering.
Usually what activists have in mind are vertebrate animals (e.g., cows, chickens, pigs). While it seems clear that vertebrate animals on factory farms live through tremendous suffering, the vertebrate animals humans eat actually make up a tiny minority of the total animals farmed and used by humans. Invertebrates (insects, molluscs, crustaceans, and others) make up the vast majority of farmed animals, and the vast majority of animals that are harmed by humans (compare the figures in these estimates to previous estimates of the scale of vertebrates in captivity). Furthermore, there are only a handful of groups working on projects that directly help these animals, and even fewer that have an EA, or even animal welfare focused approach.
In this piece, I briefly outline many (hopefully most, but I’m finding new ones regularly) of the industries that use or farm invertebrates, and provide estimates if available of the number of invertebrates killed or used annually in the industry. For industries where estimates don’t exist, I attempt to give a range in which I suspect the accurate number of individuals impacted might lie. This is meant to be the beginning of an investigation rather than the end and relies a lot on simple back-of-the-envelope calculations. I hope this piece will be a useful overview and help roughly prioritize where to invest more rigorous analysis, rather than provide an exact conclusion.
Note that this document is only about the invertebrates who are impacted directly by humans. While this includes both farmed and wild insects (e.g. black soldier flies are both killed on farms and killed by bug zappers), it does not include invertebrates harmed through fully or even partially naturogenic processes, which probably account for the vast majority of harm caused to invertebrates. It also doesn’t include many invertebrates indirectly impacted by humans, such as invertebrates who will inevitably have their lives changed by anthropogenic climate change.
Note that this summary includes some animals for whom there is little evidence demonstrating a capacity to have valenced experiences, such as bivalves. In the spirit of being comprehensive, these animals and the industries that impact them are included, though it is hard to say what our moral obligations to them might be.
Also, animal use is broken into two categories — annual deaths and used annually. “Annual deaths” indicates the number of individuals who likely die due to the industry. “Used annually” refers to animals who are not killed directly by the industry, and these animals might even have very good lives under human care. The intention of this document is to serve as a guide to the scale of industry in terms of individuals impacted, as opposed to a guide of the scale of suffering. It is to give a sense of the many ways in which invertebrate lives and welfare are entangled with our own.
This piece doesn’t include many industries which seem to minimally use invertebrates, such as the ink gall industry, which uses galls produced by wasp larvae to make ink, often after the larvae have metamorphosed and left the gall. It also doesn’t include many small industries, such as sea sponge production (which perhaps ought not be included given the lack of evidence or reason to believe that sea sponges have valenced experiences, despite being animals). I’ve included information industries that both seem somewhat large, and that I don’t think enough English language information exists to make a guess at their scale, such as the live fishing bait industry.
Which and how many invertebrates are used or killed by humans?
Below are outlines of major industries that use invertebrates, and a brief description of the industry. I provide some notes on how many individuals the industry might impact.
A full list of invertebrates used or killed by humans listed by common name can be found in this spreadsheet, although this list is not taxonomically precise, and might group animals at the order, family, or genus level. Some animals are grouped due to the estimates being not particularly precise at the species level, and others are for ease of explaining their use, to keep the list manageable.
Currently, estimates of the number of invertebrates farmed or harmed by humans are few and far between. Adding up the existing rigorous estimates, I find that at least 29 trillion to 59 trillion invertebrates are killed or used by humans annually. Note that this involves adding estimates that have different subjective confidence intervals, which might result in some issues with using it as a concrete measurement. I believe the actual count is likely an order of magnitude higher due to how little information there is on invertebrate industries.
Excluding insects killed by pesticides, I believe it is very likely that over 100 trillion (10^14) invertebrates are killed or used by humans, and possibly over 1 quadrillion (10^15). If we include insects killed by pesticides, the count could be as high as 10 quadrillion (10^16).
This means that there are at least 40 times as many invertebrates used or killed by humans than all vertebrates killed or used for food, and possibly as many as 12,000 times as many invertebrates used or killed by humans.
These estimates are dominated by members of class Insecta, primarily due to the number of insects killed by pesticides. I did not include nematodes used or killed by humans in many of my final estimates. It is extremely tricky to assess how many nematodes might be involved in human industry. I included some notes about industries that use nematodes, but unfortunately they did not make the final estimates. If I had found an approach for estimating their numerosity, nematodes might have increased the scale of these industries significantly. Besides insects, annelids, crustaceans, and molluscs are the most common animals used or killed by humans.
Note that most estimates in this are extremely speculative, and I include a rating of my subjective confidence in my sense of the scale of the industry.
| Type | Count |
|---|---|
| Invertebrates for whom rigorous estimates exist—killed annually | 7.2 trillion to 26 trillion |
| Invertebrates for whom rigorous estimates exist—used annually | 18 trillion to 40 trillion |
| Invertebrates for whom rigorous estimates exist—killed and used annually | 29 trillion to 57 trillion |
Fig. 1 — Summary of existing rigorous estimates of invertebrates killed and used by humans.
| Industry | Approximate Scale | Subjective Confidence in Accuracy of Scale | Primary Classes Impacted |
|---|---|---|---|
| Pesticides—Agricultural | 100 trillion to 10 quadrillion annual deaths | Low | Insecta |
| Food and Feed Production | 10 trillion to 100 trillion used annually, 1 trillion to 10 trillion annual deaths | Medium | Insecta, Malacostraca, Cephalopoda, Gastropoda, Bivalvia |
| Carmine / Dye Production | 4.6 trillion to 21 trillion annual deaths | High | Insecta |
| Shellac Production | 1 trillion to 100 trillion annual deaths | Low | Insecta |
| Waste Processing | 1 trillion to 100 trillion used annually | Very Low | Clitellata |
| Pesticides—Residential / Commercial | 1 trillion to 10 trillion annual deaths | Low | Insecta, Arachnida |
| Pollination and Conservation Services | 1 trillion to 10 trillion used annually | Low | Insecta |
| Silk Production | 400 billion to 1 trillion annual deaths | High | Insecta |
| Chitosan Production | 10 billion to 100 billion annual deaths | Low | Malacostraca, Insecta |
| Biological Control and Warfare | 1 billion to 1 trillion used annually | Low | Insecta, Phylum Nematoda |
| Sterile Insect Technique | 1 billion to 100 billion used annually | Low | Insecta |
| Medical Services | 1 billion to 100 billion used and deaths annually | Low | Order Xiphosura, Clitellata, Insecta |
| Fertilizer Production | < 1 billion annual deaths | Low | Malacostraca, Insecta |
| Scientific Research | 2 billion to 15 billion used annually | Low | Insecta, Phylum Nematoda |
| Education / Entertainment | 20 million to 1 billion used annually | Low | Insecta, Malacostraca, Cephalopoda |
| Pearl Production | < 10 million used annually | Low | Bivalvia |
| Fishing Bait | ??? | N/A | Clitellata, Insecta |
| Scale Wax Production | ??? | N/A | Insecta |
Fig. 2 — Summary of approximate scales of various industries that use invertebrates
Biological Control and Warfare
Industry Description
Insects, like parasitic wasps and medflies are commonly used for biological control. They are released into regions in order to reduce the populations of other insects and invertebrates. While this estimate only includes insects, nematodes are widely used for biological control as well (you can buy 250 million live nematodes for around $300 USD at time of writing). Relatedly, insects have historically been used for warfare, typically to destroy crops or to distribute pathogens.
Scale
One unpublished informal estimate of insects used for biological control estimates that between 80 and 270 billion insects are used annually for biological control. Given the informality of this estimate, I’d guess that anywhere from 10 billion to 1 trillion insects are used annually for biological control. I suspect the current number of insects used for warfare is very low.
Carmine / Dye Production
Industry Description
Carmine is a type of red dye produced by killing scale insects. While the most common type is produced from cochineals (Dactylopius coccus), a handful of other species produce related products, such as kermes and Polish cochineal. See Global Cochineal Production: Scale, Welfare Concerns, and Potential Interventions.
Scale
Probably between 4.6 trillion and 21 trillion annual deaths caused by the industry.
Chitosan Production
Industry Description
Chitosan is a widely used polysaccharide derived from the chitin of shrimp and other crustaceans. It is used for a wide variety of purposes, from winemaking to agriculture to paint production. Shrimp are the largest source of chitosan, but it can also be made from crab shells and black soldier flies.
Scale
No known estimates exist of how many invertebrates are used for chitosan production. I believe much of the shrimp used for chitosan production is also turned into food or fertilizer, but at least some shrimp, crabs, and black soldier flies are harvested exclusively for chitin. A very quick back-of-the-envelope estimate suggests that the total current chitin market requires around 30 billion shrimp to produce. I don’t know how this figure intersects with the existing estimates of shrimp farmed for food. My best guess is between 10 billion and 100 billion annual deaths are caused directly by the industry.
Education / Entertainment
Industry Description
Insects and other invertebrates are used in a variety of educational and entertainment settings. This includes invertebrates used in: building recreational and commercial butterfly habitats, zoo and aquarium collections, insect fighting, pet ownership, decoration, ceremonial releases, and recreational bug pinning.
Scale
A 2012 study estimated that 5-10 million butterfly pupae are sold annually. There are at least 5 million insect pets in South Korea. But, most of these uses of invertebrates are fairly small in scale, so the total industry seems likely to be between 20 million and 1 billion invertebrates used annually.
Fertilizer Production
Industry Description
Crabs and lobsters are a relatively uncommon fertilizer. I don’t know of any research looking into the production of these fertilizers, but I do not believe they make up a major part of the industry, or anything near the totals of crabs and lobsters caught for food. Black soldier fly and other insect frass is also sold as fertilizer, though often this is a byproduct from insect feed farms.
Scale
Unclear, probably less than 1 billion killed annually, given that total crab farming is only estimated to be 5 billion to 14 billion annually.
Fishing Bait
Industry Description
A variety of insects, annelids, and other invertebrates are raised as fishing bait. These animals are either sold dead, or are killed by either being speared with a fishing hook (seems less likely, since the point is for the worm to wiggle for the fish), or being fed live to a fish.
Scale
I believe from research into the insect farming industry that fishing bait is a very small percentage of the total industry. Artificial bait is widely used as well. I also believe most invertebrate fishing bait might be annelids. It’s pretty easy to buy up to 250 worms as bait at once. Given the low amount of information on this industry, I don’t think I can estimate its scale.
Food and Feed Production
Industry Description
Many invertebrates are used for human and animal food and animal feed, including crickets to crabs to cuttlefish to clams, humans raise or catch several phyla of invertebrates. These animals are both raised on farms and caught wild.
Scale
Estimates exist for some insects raised for food, farmed crustaceans, gastropods, and octopi (unpublished) killed for food. Estimates also exist for honeybees used in food production and pollination services (conversion to total used annually here). I haven’t found estimates for many cephalopods (e.g. squids), krill, or bivalves (clams, oysters, etc.). But, a back-of-the-envelope conversion of the 200,000 tonnes of krill killed annually, assuming a weight of 2 grams each, suggests as many 100 billion are killed annually. The total number of invertebrates killed for food is therefore likely between 1 trillion and 10 trillion killed annually, and between 10 trillion and 100 trillion are used but not killed annually in food production (mostly honeybees). Note that this estimate also includes insects used to produce beeswax, which is used in some processes outside food.
Medical Services
Industry Description
A variety of invertebrates are used in the medical industry, such as leeches used for bleeding, horseshoe crab blood used in pharmaceutical testing, or maggots used for ulcer treatment. This doesn’t include some invertebrate products listed elsewhere in this document, such as carmine used for coloring medication, shellac, snail slime, or mother-of-pearl cream.
Scale
Estimates exist for the number of horseshoe crabs used for blood, but estimates are much less clear for other insects. I believe medical maggots are often killed after being used. Treatments seem relatively infrequent in medical settings. However, there are some uses of insects that might be considered medical that are on a much larger scale, such as this factory producing traditional Chinese medicine ingredients, food, and cosmetics is using 6 billion cockroaches a year. It is unclear if these factories are counted in the insect production measures I used in my estimate of insects raised for food. My best guess is that between 1 billion and 100 billion are killed or used annually.
Pearl Production
Industry Description
While many salt-water molluscs can produce pearls, most harvested for human use come from farmed oysters and mussels. Most oysters and mussels aren’t killed as part of the harvesting process, but some die from the harvesting. Oysters can produce several pearls simultaneously.
Scale
A quick back-of-the-envelope estimate, assuming around 20 pearls produced per oyster per year, puts the total number of animals used at well under 10 million annually.
Pesticides—Agricultural
Industry Description
Insects are killed by the application of pesticides to farms, fields, and natural spaces across the globe. This is likely the single largest source of direct human impact on insects. This also includes crustaceans killed on fisheries, sea lice.
Scale
Wild Animal Initiative estimates that as many as 3.5 quadrillion insects live on insecticide treated farmland in the US alone. I don’t know what percentage of insects in a treated area are killed by pesticides, or how many treatments there are in a given year, but these insects will likely dominate any attempt to estimate the impact of pesticides. Terrestrial pesticides likely dominate, as it seems likely that only a few billion sea lice are killed annually, which likely makes up a significant fraction of aquaculture invertebrate pest treatment, but more research into the topic is needed. Total: between 100 trillion and 10 quadrillion killed annually.
Pesticides—Commercial / Residential
Industry Description
This category includes everything used to kill household pets, such as over-the-counter treatments for “pest” insects, and commercial treatments for things like termite infestations. It also includes the relatively small industries of lice, scabies, and bed bug treatment.
Scale
Global termite treatments, which are likely the single largest target of non-agricultural pesticides, likely impact fewer than 10 trillion individuals. Other industries, such as scabies and bed bug treatments, are a fraction of the scale. I estimate these industries kill between 1 and 10 trillion individuals annually.
Pollination and Conservation Services
Industry Description
Crop pollination services use bees and other insects to pollinate fields. Farmers and landowners ship beekeepers to bring bee pupae to their fields, a service that can improve yields on farms, and is essential in many industries, such as alfalfa production. Bees seem to be the most common pollinator service used. Note that this estimate does not include honeybees, which also serve as commercial pollinators — these are listed under food production. I’m also including in this estimate insects raised for conservation efforts and released into the wild.
Scale
One unpublished back-of-the-envelope estimate exists that puts the number of bees used for pollination services between 100 billion and 1 trillion alive at any given time, which I believe would put the annual number used somewhere between 1 trillion and 10 trillion insects. I don’t think other insects make up a significant portion of the individuals used for pollination and ecosystem services.
Scientific Research
Industry Description
Many invertebrates are studied in scientific labs, both as direct subjects of study, and as model organisms. In particular, fruit flies (Drosophila melanogaster) and nematodes (Caenorhabditis elegans) are widely used as model organisms. Honeybees (Apis), and a variety of other invertebrates are also widely used.
Scale
Completely unknown — I can’t find any good data on how many nematodes (including C. Elegans) might be in labs. There are at least 3,300 fruit fly labs globally (as of 2017). If each one has an average of 30,000 to 75,000 flies alive at any given time (based on an assessment from an entomologist of lab populations), and a lab lifespan of 20-45 days, that suggests an annual population of around 2 billion in labs. So given that fruit flies are the most common insect in labs, but that populations might be higher in some labs my best guess is that between 2 billion and 15 billion individuals, not including nematodes, are used in research labs annually.
Scale Wax Production
Industry Description
Chinese Scale Wax (not beeswax, which is included in food production) is produced commercially by two species of scale insects. The production seems to be primarily in China, India, and Japan, and has a handful of commercial uses, such as in polishes, and some uses in traditional Chinese medicine.
Scale
Information on industry size is extremely limited, but the market seems to be somewhat small. Production methods seem similar to cochineal and lac production, but the market seems significantly smaller. I am not making an estimate on this industry given my uncertainty.
Shellac Production
Industry Description
Shellac is a resin secreted by female lac bugs, and is used as a colorant, food glaze, and wood finish, as is in a variety of other industrial and commercial products. It’s primarily been replaced by plant-derived lacquers over the last century, but remains in use.
Scale
One unpublished estimate of total lac bug deaths, not including indirect deaths (such as nymphs), puts the annual total lac bugs killed at between 300 billion and 900 billion. Since lac bugs are related to cochineals, and given that for cochineals, the bulk of the deaths are young nymphs, we might reasonably expect 1 trillion to 100 trillion lac bugs deaths to be caused by the industry annually.
Silk Production
Industry Description
Silk is produced from boiling the cocoons of silkworms.
Scale
I produced a relatively rigorous estimate of global silkworm deaths, though it doesn’t include worms raised to adulthood for breeding purposes. I recently spoke with a staff member at INSERCO, an industry group, and now don’t believe these make up a large portion of the total. 400 billion to 1 trillion deaths annually.
Sterile Insect Technique
Industry Description
The sterile insect technique is a method for reducing insect populations by overwhelming a population with sterile male insects, causing the population to crash after a few generations. Sterile insect technique has been successfully used to eradicate screwworms from the US in the 20th century, and has been used to reduce the populations of several species of fruit flies. Now, they are being used to reduce mosquito populations in the US, Mexico, and South America.
Scale
In the 60’s and 70’s, as many as 550 million sterile screwworms were released a week in the US as part of a sterile insect program that continues today, though the volume is significantly smaller now. Given that releases are still regularly happening with millions of mosquitos and screwworms, I expect that between 1 billion and 100 billion sterile insects are released annually.
Waste Processing
Industry Description
The waste processing space is mostly limited to commercial uses of annelids and black soldier flies. Both are used for waste processing to produce fertilizer, and in the case of black soldier flies, to produce food for humans and animals.
Scale
I suspect that given that using black soldier flies for waste processing is a relatively novel idea, the vast majority of invertebrates used in waste processing are annelids. This guide to vermicomposting suggests that around 1000 worms are needed per pound of food waste. Assuming the average worm lives 3 months, and given that the largest vermicompost producer processes 50,000 metric tons a month, that suggests that at least 300 billion worms are used by this single producer. My best guess then is that the whole vermicompost industry involves the use of 1 trillion to 100 trillion individuals.
Acknowledgements
This essay is a project of Rethink Priorities. It was written by Abraham Rowe. Thanks to Daniela R. Waldhorn, Jason Schukraft, Saulius Simcikas, and Peter Hurford for helpful feedback. If you like our work, please consider subscribing to our newsletter. You can see all our work to date here.
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Thanks for the interesting post. Could you say more about the epistemic status of agricultural pesticides as the largest item in this category, e.g. what chance that in 3 years you would say another item (maybe missing from this list) is larger? And what ratio do you see between agricultural pesticides and other issues you excluded from the category (like climate change and partially naturogenic outcomes)?
(Probabilities are ballpark guesses, not rigorous)
Just in terms of insects impacted because trying to estimate nematodes or other microscopic animals gets really tricky:
Today: >99% agricultural pesticides are the largest direct cause of insect mortality
3 years: >98% agricultural pesticides are the largest direct cause of insect mortality
20 years: >95% likely agricultural pesticides are the largest direct cause of insect mortality
The one possible category I could imagine overtaking agricultural pesticides are insects raised for animal feed. I think it is fairly unlikely farming insects for human food will grow substantially, but much more likely that insects raised for poultry feed will grow in number a lot, and even more likely that insects raised for fish feed will grow a lot. There is a lot of venture capital going into raising insects for animal feed right now, so it seems at least somewhat likely some of those projects will take off (though there are cost hurdles they haven’t cleared yet compared to other animal feeds. Replacing fishmeal with insects seems even more likely because fishmeal is already a lot more expensive than grain feed.
Replacing ~40% of fishmeal with black soldier flies would put insect deaths from farming at the lower end of my current estimate for the scale of impact from agricultural pesticides. So I guess if estimates of agricultural pesticide impact are too high for an unknown reason (maybe insect populations collapse in the near future or something), there is a definite possibility, but not a big one, that insect farming could overtake pesticides in terms of deaths caused.
I am very uncertain about this. Brian Tomasik estimates the global terrestrial arthropod population to be 10^17 to 10^19 individuals, which would be 10 to 100,000 times the animals impacted by pesticides. Plausibly basically all of them could be impacted by climate change, but it’s hard to know whether or not the sign of those impacts will be negative. I imagine that most the impact from climate change, for example, would come from populations shifting—e.g. there suddenly are far fewer of an animals with survival strategy X, and a lot more of insects with survival strategy Y, and that change leads to a lot more positive or negative welfare. That being said, I think we possibly should expect ecosystems changing rapidly to be on average bad for the animals who live through that change or are born after it, at least in the short term.
I think one other excluded area I excluded that could be huge is nematodes and other microscopic invertebrates. There are obviously questions that ought to be raised about their likelihood of having valenced experiences, but as of writing I can purchase 250 million nematodes for biological control on Amazon for $135 USD. Nematodes are widely used in agriculture, and some agricultural pesticides possibly impact nematodes, implying that they’d possibly kill wild nematodes. So it seems like there is some possibility that nematodes impacted by agricultural pesticides outweigh insects impacted by them.
A very excellent post!!! A huge kudos to you.
I’m suspecting more and more that synthetic biology may be an effective career path for insect welfare—producing these compounds from cells as opposed to animals. A proof of concept already exists for carmine: https://www.nature.com/articles/s41598-018-30816-9
If there was ever something to read to prove that scope insensitivity exists, this would be it! Unreflectively, I feel about as bad about all of these industries, even though there are many orders of magnitude between the smallest and largest.
Thanks for this very valuable post!
Are there some good arguments to care about this, even for someone who feels no empathy for invertebrates?
For example the environmental impact of losing so many insects.
I think for such neglected causes focusing in secondary reasons might bring some progress.
It probably depends on the area, but probably non-welfare related impact is going to vary by industry significantly. E.g. I imagine that insecticide use has fairly substantial environmental impacts, but that residential insecticides do not. I haven’t looked into this at all, but I’d guess there are many ways in which these industries are bad and also good (they all exist because they provide some useful benefit) besides the welfare implications.