One of the stranger effects of Brexit was that, after the United Kingdom left the European Union, in 2020, it no longer recognized animals as “sentient beings.” When the U.K. was an E.U. member state, it was bound by European laws, including the Lisbon Treaty, which invoked sentience in order to shield animals from sensations such as pain, hunger, and fear. But, after Brexit, the U.K. was no longer subject to the treaty. Numerous advocacy groups demanded a replacement animal-sentience law. Twenty-nine leading veterinarians, who treated cattle, birds, fish, dogs, and other animals, sent a letter to the Daily Telegraph. “Scientific evidence demonstrates the ability of animals across a range of species to have feelings,” they wrote. “We have fought for legislation that places a duty on the state to recognise this.”
In 2021, the U.K. government introduced a bill that covered only vertebrates—animals with backbones. More protests followed. Ninety-seven per cent of animals—think clams, crabs, cicadas—are invertebrates. An octopus does not have a backbone, but in the Netflix documentary “My Octopus Teacher,” from 2020, we see one that appears curious, uses shells as body armor, and seems to bond and play with a person. In the naturalist Sy Montgomery’s nonfiction book “The Soul of an Octopus,” she visits an octopus and observes that the animal “had not only remembered us and recognized us; she had wanted to touch us again.” And whatever happened to considering the lobster?
The government asked Jonathan Birch, a philosopher at the London School of Economics, to lead an investigation into which animals should be considered sentient. Because scientists cannot ask an animal about its feelings, they tend to study whether it has a complex nervous system, and if its behaviors suggest that it experiences pain and other sensations. Birch’s team developed eight criteria for sentience and collected research into whether various species met them. (Crabs, for example, will groom injured parts of their bodies and endure a stronger electric shock in order to acquire better shells to live in.) The team ultimately helped persuade the government to recognize sentience in cephalopod mollusks, such as octopuses and squid, and decapod crustaceans, which include crabs and lobsters. Even after the government passed the Animal Welfare (Sentience) Act of 2022, however, Birch felt unsettled. The new law made no mention of the most widespread animals on earth: insects. “Once you’ve got to that stage with octopuses, you very quickly start to wonder about other invertebrates as well,” he told me.
Insects make up about forty per cent of all living species. An estimated trillion insects are farmed per year; quadrillions are killed by pesticides, and many species have gone extinct as humans have cleared habitats for farms, factories, and cities. Most of us do not think much about their inner lives, and our laws do not usually consider their welfare. Insects are small, they don’t scream or bleed red, and many are considered pests; we tend to kill or mutilate them without pause. “The default view of the vast majority of the general public, as well as many of my colleagues, is that insects are largely reflex machines,” Lars Chittka, a behavioral biologist who researches bees at Queen Mary University of London, told me. If humans seriously considered the possibility that insects are sentient, he said, we would need a “completely different connection with the natural world.”
Several years ago, Tilda Gibbons, an early-career scientist with shaggy blond hair, came across an opening for a Ph.D. student in Chittka’s lab. As an undergraduate, she had studied chronic-pain pathways, using mice as a model for humans, but she had never worked with insects. When she typed four words into Google—“Do insects feel pain?”—the search engine suggested that the answer was no. Still, Gibbons was intrigued by the question, and she joined Chittka’s team in the fall of 2019. A few months later, the U.K. went into a pandemic lockdown.
When Queen Mary University closed its laboratories, Gibbons visited campus and picked up a cardboard box with about a hundred bees. She carried it onto the London Underground and back to her apartment in East London, where she planned to study how machinelike bees really were. The box droned noisily next to her bed; her cat examined it cautiously. “It kept me awake for the first few nights,” Gibbons told me. “Then I just got used to it.”
Gibbons set up a plastic arena that contained two color-coded bee feeders. One feeder was room temperature; the other was heated to a hundred and thirty degrees Fahrenheit, roughly the temperature of hot coffee. When she filled them both with the same sugar water—four parts sugar, six parts water—the bees reliably chose the cool one. When Gibbons reduced the sugar content in the cool feeder, however, the bees sought out the hot one.
At first, the bees found ways to drink the sugar water without coming into direct contact with the hot feeder. “They were really cheeky,” Gibbons said. But, when she redesigned the feeders, forcing the bees to make contact with the heated surface if they wanted the liquid, they continued to choose the sweeter liquid in the heated feeders.
The bees in Gibbons’s experiment had satisfied at least one of the criteria developed for the Sentience Act: an animal may be sentient if it responds to “motivational trade-offs.” The bees reacted to heat in a way that was more than automatic. They put up with the heat to get a better reward. Gibbons was impressed.
The other seven criteria consider neurobiology and behavior. If an animal seeks out painkillers, or can learn based on associations with painful stimuli, that can suggest sentience. So can nociceptors, nerve cells that sense harmful stimuli—especially if the nociceptors are integrated with other sensory systems in the brain. In 2022, Gibbons worked with Birch, Chittka, and other colleagues to review research into six orders of insects, including juvenile and adult cockroaches, termites, bees, ants, butterflies, and crickets.
The literature showed insects to be far more sophisticated than one might expect of an automaton. Many have nociceptors that send signals to other parts of the insect brain, such as the central complex (associated with spatial navigation and locomotion) and the mushroom bodies (linked to learning, memory, and sensory integration). Cockroaches have a nervous-system pathway that leads up from the body to the brain and back again. In a 2019 study, researchers exposed cockroaches to a hot stimulus and a neutral stimulus; the neutral stimulus prompted a weaker signal from the body to the brain, and the hot stimulus led the roaches to try and escape. (Unsettlingly, cockroaches without heads responded to the heat but did not try to escape.) A recent genomic study of mantises, which are notorious for eating their mates during and after sex, found genes that code for nociceptive ion channels—proteins that respond to pain.
Gibbons and her colleagues ultimately found “strong evidence for pain” in adult flies, mosquitoes, cockroaches, and termites. Such insects did not appear to be at the bottom of a hierarchy of animals; they met six out of eight criteria developed for the Sentience Act, which was more than crustaceans. Other insects, like bees and butterflies, met three to four of the criteria, showing “substantial evidence” for pain. “We found no good evidence that any insects failed a criterion,” the researchers wrote.
Pain is difficult to capture. Virginia Woolf observed that a person who falls in love can draw on the words of Shakespeare or Keats. “But let a sufferer try to describe a pain,” she wrote, “and language at once runs dry.” A physician might ask a patient to rate pain on a scale from one to ten, or to pick between illustrations of faces in progressively greater distress, or to select from the McGill Pain Questionnaire, a list of seventy-eight words such as “tugging,” “sharp,” and “wretched.” The pain of nonhuman animals is even further out of reach. René Descartes believed that it was “not necessary to conceive of any vegetative or sensitive soul” to explain the actions of nonhuman animals; in his view, they were stimulus-response robots.
In a Scientific American article from 1927, Harold Bastin, a respected entomologist and photographer, reported that insects have sensory experiences that people cannot imagine: ants, for example, can see ultraviolet light. Still, he wrote, “we are faced by the extraordinary fact—attested by many students of insect psychology—that insects do not feel pain.” He described gruesome experiments that appeared to prove the point. One cut away the front part of bumblebees’ heads; the insects would still fly to flowers and try to feed. In another, a dragonfly that had had its abdomen amputated ate parts of its own body, and the “food” fell out of its gaping thorax.
In 1964, Ruth Harrison challenged the idea that animals were machinelike in her book “Animal Machines,” which uncovered the horrors of factory farming. A decade later, Peter Singer provoked mainstream interest in the experience and subjectivity of nonhuman lives. Insects, however, are generally still seen as automatons. Singer wrote, in 2017, that it was too soon to campaign for insect rights, and that we should first give “serious consideration to the interests of vertebrate animals, about whose capacity for suffering there is much less doubt.” (He has since signed in support of insect-welfare declarations.)
One of the most influential papers on the subject, “Do Insects Feel Pain?,” was published, in 1984, by C. H. Eisemann, an Australian entomologist at the University of Queensland, and several co-authors. After surveying research into the neuroscience and behavior of insects, the authors wrote that insects were unlikely to feel pain, noting that their nervous systems are different from those of vertebrates. In some experiments, insects did not seem to respond to high temperatures, electrical shocks, or bodily harm. The paper—which has hundreds of citations in entomology, comparative cognition, and animal welfare and ethics—concluded that insects follow “largely pre-programmed behavior patterns.”
It’s only very recently that other scientific perspectives on insect pain have been considered. This year, Gibbons, Chittka, and their colleagues evaluated whether bees meet a sentience criterion called “flexible self-protective behavior.” When a person bumps her elbow, she might rub it (and not her knee) to try to ease the pain. Gibbons pressed hot and unheated probes to the antennas of various bees; a control group wasn’t touched at all. She found that bees were more likely to groom antennas that had been touched by the hot probe. Gradually, her perspective on insects changed. Before she began studying them, she told me, she avoided killing bugs when she could, but she didn’t give them much more thought than that. Lately, her research has prompted her to imagine what insects are experiencing. “Maybe they were feeling something,” Gibbons said.
On a warm day last May, I met Sarah Skeels, a postdoc in Chittka’s lab, in the lobby of the biology building at Queen Mary University. Her brown hair was pulled back into a ponytail, revealing a necklace shaped like a ginkgo leaf. (She also had a bee necklace.) Skeels was studying one of the most commonly farmed insects, crickets, and her colleagues had been studying black soldier flies and their larvae. We walked upstairs and into a small room with a red overhead light. Crickets are mostly nocturnal, and red lights, which they can’t detect, minimize disruptions to their sleep cycle.
Another student leaned over the crickets, which had small numbers glued to their backs. The student had touched one cricket with an unheated probe and would now watch its grooming behavior for fifteen minutes. We watched the crickets silently for a minute or two but did not see any grooming.
In a different room, Skeels showed me a wooden box inside of which a homemade, clear-plastic tunnel forked in two directions: on one side, toward a yellow circle on the floor of the enclosure, and on the other, toward a purple one. The soft sound of chirping echoed around us. The yellow circle contained a well of sugar water and a piece of carrot, while the purple one did not; Skeels was trying to train the crickets to associate color with a reward. After that, Skeels planned to test whether they, too, engage in motivational trade-offs by exposing themselves to heat for a better reward.
