Insect Sentience: Science, Pain, Ethics, and Welfare

In my musings about animal sentience and emotions, I can’t stop wondering and worrying about insects. Do mosquitoes have emotional lives? Mosquitoes have tiny brains and lack the neural apparatus necessary for the evolution of emotions; it’s difficult to know if they do. However, we actually know more about insects than most people realize.¹

Biologist Meghan Barrett and her colleagues are concerned about the mistreatment of individual insect pollinators and in an outstanding open-access essay published in Frontiers in Ecology and Evolution titled Informing policy and practice on insect pollinator declines: Tensions between conservation and animal welfare, they argue that strict animal welfare standards should be applied to conservation efforts that focus on these insects and that the welfare of individual pollinators may be morally significant. For example, lethal sampling methods are still used to measure their populations and because these procedures have strong ethical implications they should not be used. Of course, killing other animals to study them shouldn't be used on any nonhumans.

The focus on individual pollinators is consistent with the goals of compassionate conservation in which the life of every individual matters and is morally significant, sentient or not.² It’s known that bees get depressed and a detailed review, “Can insects feel pain? A review of the neural and behavioural evidence," by Matilda Gibbons and her colleagues clearly shows that various insects are sentient and feel pain.

The science of sentience: Birch and his colleagues' eight criteria for sentience

What I found to be significant in both of the above pieces is the evidence provided by detailed scientific research. Gibbons and her colleagues relied on a seminal essay by Jonathan Birch and his colleagues called Review of the Evidence of Sentience in Cephalopod Molluscs and Decapod Crustaceans in which Birch et al. laid out and then looked for evidence on eight criteria to assess sentience in cephalopod molluscs (squid and octopus) and decapod crustaceans (shrimp, lobsters, crayfish, and crabs). These include:

1. The animal possesses receptors sensitive to noxious stimuli (nociceptors).

2: The animal possesses integrative brain regions capable of integrating information from different sensory sources.

3: The animal possesses neural pathways connecting the nociceptors to the integrative brain regions.

4. The animal’s behavioural response to a noxious stimulus is modulated by chemical compounds affecting the nervous system in either or both of the following ways: (a) The animal possesses an endogenous neurotransmitter system that modulates its responses to threatened or actual noxious stimuli; or (b) putative local anaesthetics, analgesics, anxiolytics, or anti-depressants modify an animal's responses to threatened or actual noxious stimuli.

5: The animal shows motivational trade-offs, in which the disvalue of a noxious or threatening stimulus is weighed against the value of an opportunity for reward, leading to flexible decision-making. Enough flexibility must be shown to indicate centralized, integrative processing of information involving an evaluative common currency.

6: The animal shows flexible self-protective behaviour (wound- tending, guarding, grooming, rubbing) of a type likely to involve representing the bodily location of an injury or noxious stimulus.

7: The animal shows associative learning in which noxious stimuli become associated with neutral stimuli, and or in which novel ways of avoiding noxious stimuli are learned through reinforcement.

8: The animal shows that it values a putative analgesic or anaesthetic when injured in one or more of the following ways: (a) the animal learns to self-administer putative analgesics or anaesthetics when injured; or (b) the animal learns to prefer, when injured, a location at which analgesics or anaesthetics can be accessed; or (c) the animal prioritises obtaining these compounds over other needs (such as food) when injured.

Focusing on the animals with whom they were interested, Birch et al. concluded, "We recommend that all cephalopod molluscs and decapod crustaceans be regarded as sentient animals for the purposes of UK animal welfare law. They should be counted as 'animals' for the purposes of the Animal Welfare Act 2006 and included in the scope of any future legislation relating to animal sentience."

Where do insects fall using these criteria?

Source: Cindy Gustafson/Pexels

Using the Birch et al. framework, Gibbons and her colleagues looked for different levels of scientific evidence for the presence of sentience in various insects.³ They considered six orders of insects: Coleoptera (beetles), Blattodea (cockroaches), Diptera (flies and mosquitoes), Hymenoptera (bees, wasps, sawflies, and ants), Lepidoptera (butterflies and moths) and Orthoptera (crickets, katydids, and grasshoppers).

They discovered that flies, mosquitoes, cockroaches, and termites showed strong evidence of pain, and beetles, butterflies, and moths showed substantial evidence of pain. Importantly, no insects failed any of the criteria that were used to assess their capacity for feeling pain. These data are essential to use in management, farming, and research.

They also note, "The lower confidence levels do not imply that an animal has failed the criterion—the evidence may simply be low-quality or unavailable. It is important to distinguish between absence of evidence and evidence of absence, as both are 'very low confidence' (Mallatt and Feinberg, 2022)."

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What does this research mean for understanding the biodiversity of sentience?

The science of animal sentience isn't science fiction—sentience can be found all over the place when the proper studies are conducted.⁴ Gibbons et al write, "Overall, we hope this review convinces even sceptical readers that insect pain is plausible and deserves further study."

I agree, and Barrett and her colleagues' argument that the welfare of individual insect pollinators has moral significance is totally justified.

The ethical implications of these and other data on sentience are obvious because of how insects and countless other animals are used and abused in research and conservation projects because some people think it's impossible that they are sentient beings or they casually write them off as so-called "pests." Nonetheless, detailed data show they feel morally relevant pain.

Knowing that animals are sentient should—and must—make a difference in how we view, represent, and treat them. The details—the breadth and depth—of the Birch et al. and Gibbons et al. research set an excellent example for future comparative research on many other animals. I look forward to seeing what these studies yield about the biodiversity of sentience and I'm sure that more "surprises" will be uncovered. Who'd have thought that small-brained flies, mosquitoes, cockroaches, and termites would show strong evidence of pain? In fact, they do.