I take it that your “Life span” section refers to adult lifespans? For example, the statement that “Overall, very short lifespans (less than 20 days) seem fairly rare” refers to reaching maturity in less than 20 days? Do you have estimates for life expectancy at birth (maybe ignoring egg mortality, assuming eggs aren’t sufficiently sentient to warrant concern)? Your sections on “Predators” and “Parasitoids” gave some point estimates based on when predation and inoculation by parasitoids often occur. Maybe those are reasonable approximations for life expectancy at birth. On the other hand, isn’t survivorship almost always “concave upward”, with most deaths occurring quite early? This figure is one random example, showing that most of the insects are dead before the second instar. And because of the concave-upward shape, the average age of death should be pretty young.
extended longevity associated with extended or repeated diapause
I tend to assume that insects in diapause have relatively little subjective experience, such that those periods of time “don’t count” very much if we’re using lifespan as a measure of how long the animal experiences pleasure and pain. Of course, if the insect is minimally sentient during that time, then maybe deaths occurring during that time aren’t that bad.
Extending this idea, it seems plausible that ectotherms that mature slowly in cool climates have less sentience and less hedonic experience per day than those in warm climates, because biological activity is generally slowed down in cool climates. So maybe the difference in total amount of life experiences is less than one might assume between longer-lived slow-developing insects in high latitudes vs fast-developing insects at low latitudes.
Dung beetles species had the lowest lifetime fecundity (~2 offspring), while mayflies had the largest (~4000 offspring).
If we imagine only two species of insect—one with lifetime fecundity of 2 and one with 4000 -- and if each species has equal numbers of egg-laying mothers, then the ratio of (total offspring)/(total mothers) will still be very high: (2 + 4000)/(1 + 1) = 2001. When we make assessments about the net hedonic balance of an entire ecosystem containing multiple species, it’s this average value that seems most relevant. (Of course, this number is only one heuristic. A full evaluation has to consider the sentience of each organism, the cause of death, lifespan, etc.)
I take it that your “Life span” section refers to adult lifespans?
No, this section refers to total lifespan, except where specifically noted. So 20 days is maturity AND death in 20 days (some species of aphids at very warm temperatures).
Do you have estimates for life expectancy at birth (maybe ignoring egg mortality, assuming eggs aren’t sufficiently sentient to warrant concern)?
No, this is hard. Average life expectancy at birth will vary wildly between species of terrestrial insect herbivores because of large variation in both maximum lifespan and survivorship.
Your sections on “Predators” and “Parasitoids” gave some point estimates based on when predation and inoculation by parasitoids often occur. Maybe those are reasonable approximations for life expectancy at birth.
These are lifespan expectations for individuals killed by predators or parasitoids only (and are really only gross generalizations), so they don’t represent average lifespans.
On the other hand, isn’t survivorship almost always “concave upward”, with most deaths occurring quite early? This figure is one random example, showing that most of the insects are dead before the second instar. And because of the concave-upward shape, the average age of death should be pretty young.
In short, no. As we state, the survivorship curves are wildly variable depending on the species, the location and the year. For examples of the variability please see Fig 2 from Cornell & Hawkins 1995 and Fig 1 from Hunter 2000. Different groups have different major causes of mortality, which lead to different curves. For example, endophytic species that are not leaf miners have very low mortality at the youngest ages, and experience the most loss at late juvenile or pupal stages.
I tend to assume that insects in diapause have relatively little subjective experience, such that those periods of time “don’t count” very much if we’re using lifespan as a measure of how long the animal experiences pleasure and pain. Of course, if the insect is minimally sentient during that time, then maybe deaths occurring during that time aren’t that bad.
I would be uncomfortable making this generalization. There is a gradient from simple behavioral inactivity to deep diapause, and the mechanisms of diapause are quite variable even within species groups (e.g., Hand et al. 2016).
Extending this idea, it seems plausible that ectotherms that mature slowly in cool climates have less sentience and less hedonic experience per day than those in warm climates, because biological activity is generally slowed down in cool climates. So maybe the difference in total amount of life experiences is less than one might assume between longer-lived slow-developing insects in high latitudes vs fast-developing insects at low latitudes.
This is almost certainly incorrect. A species that lives in a cool climate does not necessarily have an average experienced daily temperature that is less than a species in a warmer climate, except for really extreme cases (e.g., like comparing yearly average of species in the arctic to those at low elevation in the tropics). The temperatures experienced by insects are determined by their microclimate, which will vary with species and habitat type even on vanishingly small scales (e.g., Pincebourde & Casas 2019. It might be better to attempt such generalizations by species groups, but even that is not going to be easy (e.g., soil insects in closed canopies will experience cooler temperatures on average in the summer than leaf feeders open canopies, but warmer temperatures in the winter).
If we imagine only two species of insect—one with lifetime fecundity of 2 and one with 4000 -- and if each species has equal numbers of egg-laying mothers, then the ratio of (total offspring)/(total mothers) will still be very high: (2 + 4000)/(1 + 1) = 2001. When we make assessments about the net hedonic balance of an entire ecosystem containing multiple species, it’s this average value that seems most relevant. (Of course, this number is only one heuristic. A full evaluation has to consider the sentience of each organism, the cause of death, lifespan, etc.)
Please note that these values are extrema and are not a good representation of the distribution. The median fecundities are reported and are the best representation of the central tendency (overall 138), since the medians are seriously left-shifted from the max. Therefore, the majority of individuals will be born to parents with median fecundity.
Hand, S. C., Denlinger, D. L., Podrabsky, J. E., & Roy, R. (2016). Mechanisms of animal diapause: recent developments from nematodes, crustaceans, insects, and fish. American Journal of Physiology-Regulatory, Integrative and Comparative Physiology, 310(11), R1193-R1211. https://www.physiology.org/doi/full/10.1152/ajpregu.00250.2015
the mechanisms of diapause are quite variable even within species groups (e.g., Hand et al. 2016).
Interesting. :) When I said “I tend to assume that insects in diapause have relatively little subjective experience”, I had in mind the prototypical case of diapause where metabolism dramatically decreases.
I see that Hand et al. (2016) make the point that diapause doesn’t always imply reduced metabolism: “Diapause [...] may or may not involve a substantial depression of metabolism” and “Diapause [...] depending on the species, can also be accompanied by depression of metabolism, essential for conserving energy reserves.”
When I was reading about diapause, most of the sources suggested that metabolism was reduced, so I assumed that was the usual case. For example: “During diapause an insect’s metabolic rate drops to one tenth or less”.
I wasn’t very clear about the phrase “adult lifespan”, which I was probably using incorrectly. What I had in mind was “average lifespan only counting individuals who survive to adulthood”, which I think is similar if not the same as what you had in mind.
Life expectancy at birth may vary a lot, but I think it’d be interesting to see some example numbers to get a sense of the diversity, similar to how you gave lots of other sample numbers for other metrics. I assume one could compute it from survivorship curves. (This is just a general point for future work that people might do. You’ve already gathered a huge amount of info here, and I don’t mean to request even more. :) )
A species that lives in a cool climate does not necessarily have an average experienced daily temperature that is less than a species in a warmer climate, except for really extreme cases
My comment was partly inspired by this quote from your piece: “Species from cool temperate regions tend to have longer life cycles with about one generation per year (e.g., Danks and Foottit 1989), as do species living in areas that have a dry season. But we note that for many of these species, variable environmental conditions determine how many generations there are per year, and in addition, the overwintering generation will have a longer lifespan than growing season generations.” I didn’t read the source articles, but I was guessing that when species have longer lifespans due to cold or dry conditions, they presumably have to slow down metabolically during those unfavorable periods. And metabolic slowdown presumably means that activity by the nervous system slows down too.
I tried Googling about that and stumbled on Huestis et al. (2012). The authors expected mosquitoes to reduce metabolic rate during aestivation like happens for insects during winter diapause, but resting metabolic rate was actually higher during the late dry season. “The high ambient temperatures during the Sahelian dry season may prevent or limit a reduction in metabolic rate even if it would be adaptive.”
Still, it does seem true that insects experiencing cooler temperatures typically slow down metabolism (with your point taken that one has to consider microclimatic temperature). So I guess my point here reduces to the previous point about how winter-diapausing insects (as well as those experiencing reduced temperatures even not in diapause) plausibly matter less per unit time, in proportion to the extent of slowdown (leaving room for lots of exceptions and diversity depending on the details).
Very interesting about warm-weather diapause and metabolic rate for mosquitoes. I’ll agree that during deep cold-weather diapause insects are reducing metabolic rate (goodness, but maybe not when REALLY cold??). A quick lit search turned up seasonally variable brain size and cognitive abilities in shrews (Lázaro et al. 2018)!
No idea how this relates to lived experience tho. Extending this argument, would you also claim that species with slower metabolism have less lived experience than those with faster metabolism (e.g., “less sentience and less hedonic experience per day”), because then comparing between species with different metabolic rates is going to be quite difficult. In fact I think it quite likely that those species with faster metabolic rates have different lived experience rates than species such as humans, e.g., Healy et al. 2013.
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. https://doi.org/10.1016/j.anbehav.2013.06.018
Lázaro, J., Hertel, M., LaPoint, S., Wikelski, M., Stiehler, M., & Dechmann, D. K. (2018). Cognitive skills of common shrews (Sorex araneus) vary with seasonal changes in skull size and brain mass. Journal of Experimental Biology, 221(2), jeb166595. https://jeb.biologists.org/content/jexbio/221/2/jeb166595.full.pdf
would you also claim that species with slower metabolism have less lived experience than those with faster metabolism
Yeah, as an initial hypothesis I would guess that faster brain metabolism often means that more total information processing is occurring, although this rule isn’t perfect because the amount of information processing per unit of energy used can vary. Also, the sentience or “amount of experience” of a brain needn’t be strictly proportional to information processing.
In 2016 I wrote some amateur speculations on this idea, citing the Healy et al. (2013) paper.
There’s tons of useful info in this piece. :)
I take it that your “Life span” section refers to adult lifespans? For example, the statement that “Overall, very short lifespans (less than 20 days) seem fairly rare” refers to reaching maturity in less than 20 days? Do you have estimates for life expectancy at birth (maybe ignoring egg mortality, assuming eggs aren’t sufficiently sentient to warrant concern)? Your sections on “Predators” and “Parasitoids” gave some point estimates based on when predation and inoculation by parasitoids often occur. Maybe those are reasonable approximations for life expectancy at birth. On the other hand, isn’t survivorship almost always “concave upward”, with most deaths occurring quite early? This figure is one random example, showing that most of the insects are dead before the second instar. And because of the concave-upward shape, the average age of death should be pretty young.
I tend to assume that insects in diapause have relatively little subjective experience, such that those periods of time “don’t count” very much if we’re using lifespan as a measure of how long the animal experiences pleasure and pain. Of course, if the insect is minimally sentient during that time, then maybe deaths occurring during that time aren’t that bad.
Extending this idea, it seems plausible that ectotherms that mature slowly in cool climates have less sentience and less hedonic experience per day than those in warm climates, because biological activity is generally slowed down in cool climates. So maybe the difference in total amount of life experiences is less than one might assume between longer-lived slow-developing insects in high latitudes vs fast-developing insects at low latitudes.
If we imagine only two species of insect—one with lifetime fecundity of 2 and one with 4000 -- and if each species has equal numbers of egg-laying mothers, then the ratio of (total offspring)/(total mothers) will still be very high: (2 + 4000)/(1 + 1) = 2001. When we make assessments about the net hedonic balance of an entire ecosystem containing multiple species, it’s this average value that seems most relevant. (Of course, this number is only one heuristic. A full evaluation has to consider the sentience of each organism, the cause of death, lifespan, etc.)
There’s tons of useful info in this piece.
:) Thank-you!
I take it that your “Life span” section refers to adult lifespans?
No, this section refers to total lifespan, except where specifically noted. So 20 days is maturity AND death in 20 days (some species of aphids at very warm temperatures).
Do you have estimates for life expectancy at birth (maybe ignoring egg mortality, assuming eggs aren’t sufficiently sentient to warrant concern)?
No, this is hard. Average life expectancy at birth will vary wildly between species of terrestrial insect herbivores because of large variation in both maximum lifespan and survivorship.
Your sections on “Predators” and “Parasitoids” gave some point estimates based on when predation and inoculation by parasitoids often occur. Maybe those are reasonable approximations for life expectancy at birth.
These are lifespan expectations for individuals killed by predators or parasitoids only (and are really only gross generalizations), so they don’t represent average lifespans.
On the other hand, isn’t survivorship almost always “concave upward”, with most deaths occurring quite early? This figure is one random example, showing that most of the insects are dead before the second instar. And because of the concave-upward shape, the average age of death should be pretty young.
In short, no. As we state, the survivorship curves are wildly variable depending on the species, the location and the year. For examples of the variability please see Fig 2 from Cornell & Hawkins 1995 and Fig 1 from Hunter 2000. Different groups have different major causes of mortality, which lead to different curves. For example, endophytic species that are not leaf miners have very low mortality at the youngest ages, and experience the most loss at late juvenile or pupal stages.
I tend to assume that insects in diapause have relatively little subjective experience, such that those periods of time “don’t count” very much if we’re using lifespan as a measure of how long the animal experiences pleasure and pain. Of course, if the insect is minimally sentient during that time, then maybe deaths occurring during that time aren’t that bad.
I would be uncomfortable making this generalization. There is a gradient from simple behavioral inactivity to deep diapause, and the mechanisms of diapause are quite variable even within species groups (e.g., Hand et al. 2016).
Extending this idea, it seems plausible that ectotherms that mature slowly in cool climates have less sentience and less hedonic experience per day than those in warm climates, because biological activity is generally slowed down in cool climates. So maybe the difference in total amount of life experiences is less than one might assume between longer-lived slow-developing insects in high latitudes vs fast-developing insects at low latitudes.
This is almost certainly incorrect. A species that lives in a cool climate does not necessarily have an average experienced daily temperature that is less than a species in a warmer climate, except for really extreme cases (e.g., like comparing yearly average of species in the arctic to those at low elevation in the tropics). The temperatures experienced by insects are determined by their microclimate, which will vary with species and habitat type even on vanishingly small scales (e.g., Pincebourde & Casas 2019. It might be better to attempt such generalizations by species groups, but even that is not going to be easy (e.g., soil insects in closed canopies will experience cooler temperatures on average in the summer than leaf feeders open canopies, but warmer temperatures in the winter).
If we imagine only two species of insect—one with lifetime fecundity of 2 and one with 4000 -- and if each species has equal numbers of egg-laying mothers, then the ratio of (total offspring)/(total mothers) will still be very high: (2 + 4000)/(1 + 1) = 2001. When we make assessments about the net hedonic balance of an entire ecosystem containing multiple species, it’s this average value that seems most relevant. (Of course, this number is only one heuristic. A full evaluation has to consider the sentience of each organism, the cause of death, lifespan, etc.)
Please note that these values are extrema and are not a good representation of the distribution. The median fecundities are reported and are the best representation of the central tendency (overall 138), since the medians are seriously left-shifted from the max. Therefore, the majority of individuals will be born to parents with median fecundity.
References Cornell, H. V., & Hawkins, B. A. (1995). Survival patterns and mortality sources of herbivorous insects: some demographic trends. The American Naturalist, 145(4), 563-593. https://www.journals.uchicago.edu/doi/abs/10.1086/285756
Hand, S. C., Denlinger, D. L., Podrabsky, J. E., & Roy, R. (2016). Mechanisms of animal diapause: recent developments from nematodes, crustaceans, insects, and fish. American Journal of Physiology-Regulatory, Integrative and Comparative Physiology, 310(11), R1193-R1211. https://www.physiology.org/doi/full/10.1152/ajpregu.00250.2015
Hunter, A. F. (2000). Gregariousness and repellent defences in the survival of phytophagous insects. Oikos, 91(2), 213-224.https://doi.org/10.1034/j.1600-0706.2000.910202.x
Pincebourde, S., & Casas, J. (2019). Narrow safety margin in the phyllosphere during thermal extremes. Proceedings of the National Academy of Sciences, 116(12), 5588-5596. https://www.pnas.org/content/pnas/116/12/5588.full.pdf
Interesting. :) When I said “I tend to assume that insects in diapause have relatively little subjective experience”, I had in mind the prototypical case of diapause where metabolism dramatically decreases.
I see that Hand et al. (2016) make the point that diapause doesn’t always imply reduced metabolism: “Diapause [...] may or may not involve a substantial depression of metabolism” and “Diapause [...] depending on the species, can also be accompanied by depression of metabolism, essential for conserving energy reserves.”
When I was reading about diapause, most of the sources suggested that metabolism was reduced, so I assumed that was the usual case. For example: “During diapause an insect’s metabolic rate drops to one tenth or less”.
Thanks for the further insights. :)
I wasn’t very clear about the phrase “adult lifespan”, which I was probably using incorrectly. What I had in mind was “average lifespan only counting individuals who survive to adulthood”, which I think is similar if not the same as what you had in mind.
Life expectancy at birth may vary a lot, but I think it’d be interesting to see some example numbers to get a sense of the diversity, similar to how you gave lots of other sample numbers for other metrics. I assume one could compute it from survivorship curves. (This is just a general point for future work that people might do. You’ve already gathered a huge amount of info here, and I don’t mean to request even more. :) )
My comment was partly inspired by this quote from your piece: “Species from cool temperate regions tend to have longer life cycles with about one generation per year (e.g., Danks and Foottit 1989), as do species living in areas that have a dry season. But we note that for many of these species, variable environmental conditions determine how many generations there are per year, and in addition, the overwintering generation will have a longer lifespan than growing season generations.” I didn’t read the source articles, but I was guessing that when species have longer lifespans due to cold or dry conditions, they presumably have to slow down metabolically during those unfavorable periods. And metabolic slowdown presumably means that activity by the nervous system slows down too.
I tried Googling about that and stumbled on Huestis et al. (2012). The authors expected mosquitoes to reduce metabolic rate during aestivation like happens for insects during winter diapause, but resting metabolic rate was actually higher during the late dry season. “The high ambient temperatures during the Sahelian dry season may prevent or limit a reduction in metabolic rate even if it would be adaptive.”
Still, it does seem true that insects experiencing cooler temperatures typically slow down metabolism (with your point taken that one has to consider microclimatic temperature). So I guess my point here reduces to the previous point about how winter-diapausing insects (as well as those experiencing reduced temperatures even not in diapause) plausibly matter less per unit time, in proportion to the extent of slowdown (leaving room for lots of exceptions and diversity depending on the details).
Very interesting about warm-weather diapause and metabolic rate for mosquitoes. I’ll agree that during deep cold-weather diapause insects are reducing metabolic rate (goodness, but maybe not when REALLY cold??). A quick lit search turned up seasonally variable brain size and cognitive abilities in shrews (Lázaro et al. 2018)!
No idea how this relates to lived experience tho. Extending this argument, would you also claim that species with slower metabolism have less lived experience than those with faster metabolism (e.g., “less sentience and less hedonic experience per day”), because then comparing between species with different metabolic rates is going to be quite difficult. In fact I think it quite likely that those species with faster metabolic rates have different lived experience rates than species such as humans, e.g., Healy et al. 2013.
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. https://doi.org/10.1016/j.anbehav.2013.06.018
Lázaro, J., Hertel, M., LaPoint, S., Wikelski, M., Stiehler, M., & Dechmann, D. K. (2018). Cognitive skills of common shrews (Sorex araneus) vary with seasonal changes in skull size and brain mass. Journal of Experimental Biology, 221(2), jeb166595. https://jeb.biologists.org/content/jexbio/221/2/jeb166595.full.pdf
That shrew thing is fascinating!
Yeah, as an initial hypothesis I would guess that faster brain metabolism often means that more total information processing is occurring, although this rule isn’t perfect because the amount of information processing per unit of energy used can vary. Also, the sentience or “amount of experience” of a brain needn’t be strictly proportional to information processing.
In 2016 I wrote some amateur speculations on this idea, citing the Healy et al. (2013) paper.