Six-legged suffering

8 September 2025

A growing number of biologists believe that insects could be sentient, and that we must do more to minimise any pain or stress we cause them. Tom Ireland examines the evidence

Nobody knows quite how many insects are used in research and education each year. One estimate from 2022 suggests it could be between two and 15 billion individuals¹. From ladybirds caught in yoghurt pots at preschool to Drosophila bred in their millions for laboratories around the world, insects are generally seen as fair game for us to prod, poke and far worse to progress our understanding and exploitation of nature. 

Beyond science, the number of insects killed by humans reaches a scale that is difficult to comprehend. Those exterminated for agriculture, or farmed to produce food, feed, fibres or dyes, could be in the quadrillions every year².

There are virtually no animal welfare laws anywhere in the world to protect insects, meaning that our planet’s most abundant and diverse animal class can be subjected to any procedures that we deem necessary: death by neurotoxin, freezing, boiling or grinding. 

Entomological ethics

In recent years entomologists and neurobiologists have started to revisit the possibility that insects have some degree of sentience, or might have the capacity to experience pain or stress (or, for those who prefer less anthropomorphic language, a ‘negatively valenced welfare state’).

A number of books have been published on the topic and specialists have also written recently about how their views have changed over time, such as Lars Chittka, a professor of sensory and behavioural ecology at Queen Mary University of London. Chittka once thought a colleague had “lost their mind” for worrying about the welfare of lab insects, but has since written extensively about insect emotion and stress, including in his book The Mind of a Bee.  

In 2023 the Insect Welfare Research Society was founded, reflecting the growing need to connect and support researchers working on the topic, and in the same year the Royal Entomological Society started a special interest group on welfare and ethics. 

Insect sentience was dismissed as implausible for most of the 20th century. But the number of researchers, groups and societies exploring it is on the rise 

With no way to directly measure the subjective internal experience of an insect, the question of insect sentience requires scientists to look at organisms’ behaviour and cognitive abilities, and assess whether sentience might be physiologically possible and evolutionarily beneficial. 

Arguments that insect sentience and suffering is at least plausible often highlight their amazingly diverse and surprisingly sophisticated behaviours and types of learning, while opponents argue that robots or computers could be programmed to perform similar tasks, but would never be thought of as conscious. 

With our use of insects for food and feed set to increase hugely in the coming decades, the topic has become a fast-moving and contentious area of research, and the evidence to help inform the debate is steadily growing. 

Criteria for consciousness

In 2020 the UK Government asked Professor Jonathan Birch, a specialist in the philosophy of the biological sciences at the London School of Economics, to lead a study investigating which animals should be considered sentient. Birch and his team went on to develop eight criteria for sentience, which ultimately led to the UK recognising invertebrates such as octopus, squid, crabs and lobsters as sentient beings in the Animal Welfare (Sentience) Act 2022. 

When insects were not mentioned in the legislation, a group of scientists, including Birch and Chittka, decided to explore whether insects could feel pain by examining the neural and behavioural evidence³. Using the eight criteria, they found that certain orders – including Diptera (flies and mosquitoes) and Blattodea (cockroaches and termites) – satisfied six of eight criteria, constituting “strong evidence for pain”, and in fact scoring higher than some animals recognised in the new animal welfare legislation. 

Adults of other insect orders satisfied three to four criteria, which the authors considered “substantial evidence for pain”. The authors stressed that it was often the paucity of good-quality research that prevented certain orders from satisfying more criteria. 

  A 2022 study found that two insect orders in particular scored very highly on Birch's eight criteria for sentience. 

Behavioural evidence

Beyond Birch’s pain sensation framework, researchers arguing that sentience is at least plausible can point to an ever-expanding range of cognitive feats demonstrated in insects, some of which are strongly associated with consciousness or an internal ‘reality model’ in other animals. These include counting, addition and subtraction (bees); an understanding of the concepts of same and different (wasps and bees); tool use (ants); facial recognition (wasps), play-like behaviour (bees and flies), knowledge of body dimensions (bees); and social information transfer in many types of insect.

Researchers have also devised studies that suggest insects are capable of ‘metacognitive-like processes’, ‘attention’ and surprisingly flexible types of learning and decision-making². And an increasing number of studies have found that insects can have internal states that influence their perception and decision-making^⁴,⁵, inducing both optimistic and pessimistic cognitive biases. These judgement bias tests are similar to those used to assess the welfare and emotional states of higher animals, such as captive rats, and some say these states should be seen as analogous to emotions such as stress, anxiety or fear.

Observations of ants going about their business with broken legs has long been used as evidence that insects do not experience pain like higher animals. 

A further range of behaviours – including individuals grooming their injuries, caring for offspring, giving gifts, performing courtship dances and songs, communicating distress, and rescuing kin from other animals or when trapped or buried – invites us to see insects as complex animals and anthropomorphise their motivations.  

Chittka, who leads the Bee Sensory and Behavioural Ecology Lab at Queen Mary University, has even argued that the striking individual variation in behaviour and preferences observed in bees of the same species could be analogues of ‘personalities’, with some bees showing intrepid and brave attributes, and others seemingly lazy and rebellious. 

Others approach the topic from an evolutionary perspective, asking why consciousness arises and whether it would be beneficial for insects to have it. “[Consciousness] motivates animals to get the good and avoid the bad, and it helps them set priorities, where stronger feelings signal more value or disvalue,” writes Bob Fischer, professor of philosophy at Texas State University and prominent blogger on animal sentience. “Those are pretty basic needs for organisms that need to move around in the world, balancing risks with opportunities. It’s plausible, then, that sentience evolved early in the history of life⁶.”

The case against

The highly cited 1984 review ‘Do Insects Feel Pain?’, by Australian entomologist CH Eisemann⁷, was an influential starting point for the case against insect sentience. Eisemann concluded that the nervous systems of insects were too different and simple for insects to feel pain like we do, and highlighted cases of insects seemingly going about their business when they should be incapacitated by overwhelming sensations of pain. 

Ants walking with broken legs, mantids continuing to mate while being eaten and various species of insects continuing to feed even as food spills directly out of their open entrails are still used as evidence that insects are oblivious, machine-like organisms.  

Indeed nociception – the detection of noxious stimuli and behavioural responses to it – can and does occur without the subjective, conscious and unpleasant experience of pain. This can be seen in the reflex that causes our hand to withdraw instantly from a hot stove, when nerve impulses are transmitted via a neural circuit that goes from the hand to the spinal cord and back. Pain is experienced soon after, in our minds, but the body is capable of reacting to the stimulus faster without it. 

Similarly, an unthinking computer or robot could be designed to learn or react to stimuli in the same complex ways insects do. Amazingly sophisticated, adaptive and seemingly emotional responses can emerge from neural circuits without any subjective internal experience, as artificial intelligence platforms increasingly show. 

And as interesting as the thought of a lazy, rebellious bee is, striking differences between individuals of the same species are still not evidence that bees have personalities, a private internal experience or ‘feelings’. As German neuroscientist Björn Brembs has suggested, having some inbuilt ‘noise’ in the nervous system, to create a certain amount of behavioural variety, can make a community of individuals more innovative and less predictable to predators. 

Pain and the insect brain

Dr Shelley Adamo, a professor at Dalhousie University and expert in invertebrate behavioural psychology, has argued that insects do not appear to possess the network of brain regions that together create the unpleasant experience of pain in humans, which requires connections between areas associated with self-awareness, emotion and memory. “Insect nociception is processed largely in two higher-order areas in the brain: the mushroom bodies and the central complex,” she writes in a 2019 review paper⁸. “There is little evidence of a coordinated pain network that would integrate these two areas with each other along with other traits thought to be important for a pain experience in humans.” 

Furthermore, insects also lack any structure comparable to the amygdala, which plays a central role in coordinating emotional responses to pain in higher animals. 

Adamo recognises, however, that it is still possible that insects “could have a modest pain experience using a less integrated neural circuit”; and recent work to map the entire Drosophila melanogaster ‘connectome’ has shown these fruit flies do in fact have connections between different regions of the brain that process noxious stimuli⁹. 

Other sceptics of insect sentience feel that many inferences entomologists make about the results of behavioural studies are too subjective and speculative. For example, studies that found bees will roll tiny balls around a designated ‘play area’, for no reward, are often cited as evidence that the bees simply enjoy it and are therefore playing (or even that they are ‘joyful’)¹⁰. Yet we do not truly know why they are doing it, let alone how they feel when they do it. 

Observations of insects carrying on as normal when catastrophically injured remain influential. However, researchers such as Meghan Barrett, assistant professor of biology at Indiana University Indianapolis, have begun to argue that these cases may not be as compelling as they seem¹¹. She argues that, first, these observations are rare, and the very fact that they are unusual creates an observation and reporting bias. (One can also find examples of humans continuing on with terrible injuries to reach safety, or to complete a sporting event, or living for years with chronic pain, which does not mean humans do not feel pain.) There are far more studies where insects show reduced activity when injured, and some showing that major injuries to a limb can result in increased sensitivity to things like temperature, analogous with peripheral nerve injuries in humans.

Further, the physics and body composition of insects are so different to those of humans and large animals that it is difficult to make comparisons about how much pain an injury should cause, Barrett argues. For example, a six-legged ant that weighs a few milligrams might be able to walk on a broken leg in a way a larger two-legged animal couldn’t, and therefore the pain it might experience is not directly comparable. 

Seeking relief

Hypothetically, the most compelling evidence for insect pain would be studies that could show insects will seek out pain-relieving substances when badly injured. Why else would an insect with simple machine-like reflexes to noxious stimuli ingest a substance that interferes with these essential signals, other than to relieve the unpleasant sensation? 

However, evidence here is not strong. Several studies have shown that analgesic or anxiolytic substances can dampen insects’ response to noxious substances – for example, bees given ethanol are less likely to sting in response to electric shocks, and morphine-addled cockroaches take longer to respond to and escape from high temperatures³. Studies have also shown fruit flies self-administering ethanol and psychotropic drugs, and bees self-administering nicotine, but the insects studied in this case were healthy, not injured.  

No studies have yet conclusively shown that injured insects actively choose to relieve injuries with analgesic substances, and indeed some have shown insects avoid them, possibly due to their bitter taste³. It remains a key area for further research. 

Painful progress

In 2020, sensing that researchers would reach an impasse on the broader question of insect sentience, Birch began to think about new approaches that might help progress towards a less speculative view. 

Drosophila are bred for scientific research in their billions - should we care more about their welfare?

Central to his suggested approach is a set of experimental methods in cognitive science known as ‘masking’. These are ways of delivering a stimulus in human studies (or higher animals) so it is experienced unconsciously. Scientists, he argues, should explore how cognitive abilities linked with consciousness are affected when the stimulus is masked. 

“Suppose we find evidence of a cluster of consciousness-linked abilities, switching off and on together with masking, and coming and going together over phylogenetic time,” he writes¹². “This would, I suggest, allow a much more secure inference… to the presence of consciousness than any single marker in isolation, or even any checklist of markers that have not been shown to reliably cluster together.”

Further research on insect sentience is clearly needed and the answer may not be simple. As the most diverse animal order on Earth, insects should be expected to have exceptionally diverse cognitive powers, perhaps a greater range than we see in vertebrates.    

In the meantime, new measures could be introduced to gain a deeper understanding of the wellbeing of the insects we use. Monitoring escape and avoidance behaviours, the presence of injuries and diseases, changes in gene expression or stress hormone levels, or longevity and other measures, could be used in addition to just using growth rates as an indication of overall health. 

If we accept that there is a continuum of cognitive sophistication in the animal world, where consciousness emerges at some point along it, then we must do our best to understand where that point is with some degree of precision – and where life’s extraordinary capacity for subjective experience, and suffering, begins.

REFERENCES

1) Rowe, A. The scale of direct human impact on invertebrates. OSF Preprint (2020). 

2) Barrett, M. Pain and suffering in farmed animals: first steps towards better understanding and management – insects. OSF Preprints (29 February 2024).

3) Gibbons, M. et al. Chapter Three: Can insects feel pain? A review of the neural and behavioural evidence. Adv. Insect Physiol. 63, 155–229 (2022). 

4) Procenko, O.P. et al. Physically stressed bees expect less reward in an active choice judgement bias test. Proc. R. Soc. B. 291(2032), 29120240512 (2024). 

5) Amanda, D. et al. State-dependent judgement bias in Drosophila: evidence for evolutionarily primitive affective processes. Biol. Lett. 14(2) 1420170779 (2018). 

6) Bekoff, M. The Current state of the science of insect sentience. Interview with Dr Bob Fischer. Psychol. Today (3 May 2024). 

7) Eisemann, C.H. et al. Do insects feel pain? A biological view. Experientia 40, 164–167 (1984). 

8) Adamo, S. Is it pain if it does not hurt? On the unlikelihood of insect pain. Can. Entomol. 151(6), 685–695 (2019). 

9) Li, F. et al. The connectome of the adult Drosophila mushroom body provides insights into function. eLife 9:e62576 (2020). 

10) Chittka, L. Do insects feel joy and pain? Si. Am. (July 2023). 

11) Barret, M. & Fischer, B. The Era Beyond Eisemann et al. (1984): insect pain in the 21st century. Preprint, publication due in Q. Rev. Biol September 2025. 

12) Birch, J. The search for invertebrate consciousness. Nous 56(1) (2022). 

Tom Ireland MRSB is editor of The Biologist