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.
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.
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.
Questions on the study results should be directed to Dr. Lars Chittka, the corresponding author, here: email@example.com
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.