Do insects have feelings? Love or Hate? What’s your opinion
The entomology literature has historically suggested insects cannot feel pain, leading to their exclusion from ethical debates and animal welfare legislation. However, there may be more neural and cognitive/behavioural evidence for pain in insects than previously considered. We use Birch et al. 's (2021) eight criteria for sentience to critically evaluate the evidence for pain in insects. We assess six orders (Blattodea, Coleoptera, Diptera, Hymenoptera, Lepidoptera, and Orthoptera) in at least two life stages (adult and first instarjuveniles, as well as other instars where relevant data are found). Other insect orders have not received enough research effort to be evaluated. According to the Birch et al. framework, adult Diptera (flies and mosquitoes) and Blattodea (cockroaches and termites) satisfy six criteria, constituting strong evidence for pain. Adults of the remaining orders (except Coleoptera, beetles) and some juveniles (Blattodea and Diptera, as well as last instar Lepidoptera [butterflies and moths]) satisfy 3–4 criteria, or “substantial evidence for pain”. We found no good evidence that any insects failed a criterion. However, there were significant evidence gaps, particularly for juveniles, highlighting the importance of more research on insect pain. We conclude by considering the ethical implications of our findings where insects are managed in wild, farmed, and research contexts.
How we evaluate evidence for pain
In a report commissioned by the UK government, Birch et al. (2021) developed a new framework for evaluating evidence of animal sentience, with a focus on pain (later published as Crump et al., 2022). Birch et al. (2021) write that “pain is one example within a broader category of negatively-valenced affective states, a category which also includes states of anxiety, fear, hunger, thirst, coldness, discomfort and boredom” (Birch et al., 2021, p. 12). Building on previous work (e.g., Bateson, 1991
Criterion 1: Nociception
The animal possesses receptors sensitive to noxious (i.e., potentially or actually harmful, damaging) stimuli (nociceptors)
This criterion specifies the most basic prerequisite for experiencing pain. If fulfilled, the animal has the neurobiological capacity for nociception. Vertebrates detect noxious stimuli through specialised peripheral sensory neurons: nociceptive neurons (Dubin and Patapoutian, 2010), characterised by free nerve endings under the epidermis.
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Summary of evidence for insect pain
In Section 3, we assessed the evidence for k my each criterion in adults and juveniles of six insect orders. Table 11 summarises our confidence levels for adults, and Table 12 summarises our ratings for first (and last) instar juveniles.
Birch et al. (2021) suggested an approximate grading scheme for communicating the strength of evidence for sentience (specifically for pain). The five grades were:
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1.
Very strong evidence: High or very high confidence that 7–8 criteria are satisfied. Welfare protection
Ethical considerations for the use or management of insects
Insects are managed in a variety of contexts that may raise welfare concerns, including the food and feed industry, silk/shellac/dye production, waste management, pest/invasive species management, wildlife conservation, beekeeping, zoos and insectariums, research/education settings, the entertainment industry, in medicine, and as pets. By far, the largest number of insects with welfare impacted by human management will be in wild/agricultural settings, followed by the growing insects as food
Conclusion
Using the Birch et al. (2021) framework, we reviewed the evidence for sentience (and specifically pain) in six insect orders across their development. We found “strong evidence” for pain experiences in adults of two orders, Diptera (flies and mosquitoes) and Blattodea (cockroaches and termites). There was also “substantial evidence” in adult Hymenoptera (bees, wasps, ants, and sawflies), Orthoptera (crickets and grasshoppers), and Lepidoptera (butterflies and moths), and “some evidence” in
Acknowledgements
We thank Elisabetta Versace, Katrin Vogt, Nikita Komarov and Frederic Libersat for their feedback on the manuscript.
Conflict of interest
Meghan Barrett reports a relationship with Rethink Priorities that includes: consulting.
Funding statement
This research is part of a project that has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme, Grant Number 851145. M.G. received funding from a Queen Mary University of London PhD Studentship. M.B. is currently funded as an NSF postdoctoral research fellow (2109399).
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