This short research summary briefly highlights the major results of a new publication on the scientific evidence for insect pain in Advances in Insect Physiology by Gibbons et al. (2022). This EA Forum post was prepared by Meghan Barrett, Lars Chittka, Andrew Crump, Matilda Gibbons, and Sajedeh Sarlak.
The 75-page publication summarizes over 350 scientific studies to assess the scientific evidence for pain across six orders of insects at, minimally, two developmental time points (juvenile, adult). In addition, the paper discusses the use and management of insects in farmed, wild, and research contexts. The publication in its entirety can be reviewed here. The original publication was authored by Matilda Gibbons, Andrew Crump, Meghan Barrett, Sajedeh Sarlak, Jonathan Birch, and Lars Chittka.
Major Takeaway
We find strong evidence for pain in adult insects of two orders (Blattodea: cockroaches and termites; Diptera: flies and mosquitoes). We find substantial evidence for pain in adult insects of three additional orders, as well as some juveniles. For several criteria, evidence was distributed across the insect phylogeny, providing some reason to believe that certain kinds of evidence for pain will be found in other taxa. Trillions of insects are directly impacted by humans each year (farmed, managed, killed, etc.). Significant welfare concerns have been identified as the result of human activities. Insect welfare is both completely unregulated and infrequently researched.
Given the evidence reviewed in Gibbons et al. (2022), insect welfare is both important and highly neglected.
Research Summary
- The Birch et al. (2021) framework, which the UK government has applied to assess evidence for animal pain, uses eight neural and behavioral criteria to assess the likelihood for sentience in invertebrates: 1) nociception; 2) sensory integration; 3) integrated nociception; 4) analgesia; 5) motivational trade-offs; 6) flexible self-protection; 7) associative learning; and 8) analgesia preference.
- Definitions of these criteria can be found on pages 4 & 5 of the publication's main text.
- Gibbons et al. (2022) applies the framework to six orders of insects at, minimally, two developmental time points per order (juvenile, adult).
- Insect orders assessed: Blattodea (cockroaches, termites), Coleoptera (beetles), Diptera (flies, mosquitoes), Hymenoptera (bees, ants, wasps, sawflies), Lepidoptera (butterflies, moths), Orthoptera (crickets, katydids, grasshoppers).
- Adult Blattodea and Diptera meet 6/8 criteria to a high or very high level of confidence, constituting strong evidence for pain (see Table 1, below). This is stronger evidence for pain than Birch et al. (2021) found for decapod crustaceans (5/8), which are currently protected via the UK Animal Welfare (Sentience) Act 2022.
- Adults of the remaining orders (except Coleoptera) and some juveniles (Blattodea, Diptera, and last juvenile stage Lepidoptera) satisfy 3 or 4 criteria, constituting substantial evidence for pain (see Tables 1 + 2).
- We found no good evidence that any insect failed a criterion.
- For several criteria, evidence was distributed across the insect phylogeny (Figure 1), including across the major split between the hemimetabolous (incomplete metamorphosis) and holometabolous (complete metamorphosis) insects. This provides some reason to believe that certain kinds of evidence for pain (e.g., integrated nociception in adults) will be found in other taxa.
- Our review demonstrates that there are many areas of insect pain research that have been completely unexplored. Research gaps are particularly substantial for juveniles, highlighting the need for more work across developmental stages.
- Additionally, our review could not capture within-order variation in neuroanatomical development or behavior, as most data within an order were from only one or two species. Further research on within-order variation, particularly for juveniles, will be necessary.
Table 1. Confidence level for each criterion for adults of each focal insect order.
Table 2. Confidence level for each criterion for juveniles of each focal insect order.
Contact Information
Questions on the study results should be directed to Dr. Lars Chittka, the corresponding author, here: l.chittka@qmul.ac.uk
Questions on how the effective altruism community can improve insects’ lives can be directed to Rethink Priorities here; and/or by emailing Dr. Meghan Barrett, here: meghan@rethinkpriorities.org
Acknowledgements
Barrett collaborates with Rethink Priorities on topics related to insect welfare. However, this project was not funded by or associated with Rethink Priorities and was conducted independently by Barrett, in collaboration with Gibbons, Crump, Sarlak, Chittka, and Birch.
I replied to your comment before you edited it and added the following, so I will make quick replies to these new questions throughout.
To the extent that we found research on these orders O and criteria C, each of the orders satisfies each of the criteria.
- I would rephrase: For the OxC combinations that we found enough research to make a determination about whether each order O satisfies or fails each criterion C, we found that each order satisfied each criterion.
We are not saying anything about the degree to which a particular O satisfies a particular C. [Uhm, I am not sure why. Are the criteria extremely binary, even if you measure them statistically? Or were you looking at the degrees, and every O satisfied every C to a high enough degree that you just decided not to talk about it in the post?]
- These criteria, like many in science, are actually particularly binary. E.g., you either have nociceptors or you do not have nociceptors (you either are an insect, or you are not an insect!). So, in this way, we are assessing satisfaction/failure in a binary sense.
- But, of course, there are relevant degrees that emerge after determining satisfaction or failure. For example, you might have more types or fewer types of nociceptors. They might be expressed in greater or fewer numbers. Ion channels could be expressed in different types of cells or sequestered on the interior of the cell following expression for different amounts of time/due to different physiological causes. In all cases, these degrees would not change our determination about whether the animal group possesses nociceptors (e.g., satisfies/fails the criterion). But, of course, these degrees might have some relevant effects on our eventual credence for pain! We do spend some time on this in the paper (which is 75 pages and I could not replicate here! But see criterion 7 for some of this light discussion of degrees).
- To my mind, the point of this framework, and determining pass/fail for the criterion, is to 1) determine whether it is worth taking the idea of pain seriously in an animal group (e.g., providing evidence for or against applying some version of a precautionary principle); and 2) determining where we should direct research effort by identifying areas where we don’t yet have high-quality evidence for or against the satisfaction of criteria that might be relevant to insect pain.
To recap: you don't talk about the degrees-of-satisfying-criteria, and any research that existed pointed towards sufficient-degree-of-C, for any O and C. Given this, the tables in this post essentially just depict "How much quality-adjusted research we found on this."
- We talk about this briefly, for criterion 7, but to be clear, there was relatively little ‘degrees-of-satisfying’ evidence to be found in insects at this time. In most OxC cases, as the table demonstrates, there wasn’t even sufficient evidence to demonstrate with high/very high confidence that the order met or failed to meet the binary condition of the criterion – much less the degrees of meeting/failure, after having met or failed it.
In particular, the tables do not depict anything like "Do we think these insects can feel pain, according to this measure?". Actually, you believe that probably once there is enough high-quality research, the research will conclude that all insects will satisfy all of the criteria. (Or all orders of insects sufficiently similar to the ones you studied.)
[Here, I mean "believe" in the Bayesian sense where if you had to bet, this is what you would bet on. Not in the sense of you being confident that all the research will come up this way. In particular, no offense meant by this :-) .]
- I don’t really understand the first part of this. But I guess I would say that the table itself doesn’t represent any particular quantifiable credence that insects feel pain. However, the summation of these lines of evidence can provide some traction for thinking about how seriously to take the idea of insect pain at all - even if it again doesn't give us any particular credence level.
- Re: point 2, I strongly disagree that this is my belief. I believe that once there is enough high quality research for each criterion and order, we will be able to conclude whether or not insect orders satisfy or fail all criteria. There are a select few criteria where available evidence suggests that we might bet on more research coming up satisfactorily – e.g., criterion 3 in adults, where evidence for integrated nociception is distributed across the phylogeny and criterions 1 + 2 (the preconditions) are also robustly met, plus we know that both 1 + 2 are robustly conserved across all the insect orders. However, in most O x C cases we have very, very little data – or even no real data (criterion 8, particularly!) – that can lead us to make any specific or generalizable conclusions about the likelihood of any or all insects meeting that criterion.
This comment is representative only of MRB's opinions and expertise, and not the other post/publication authors.