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Do Insects Feel Pain?: New research finds ‘strong evidence’ that they are sentient

Insects are small, they don’t scream or bleed red, and many are considered pests; we tend to kill or mutilate them without pause. Most of us do not think much about their inner lives, and our laws do not usually consider their welfare. Yet, the research literature show insects to be far more sentient than one might expect. 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). 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.

SHAYLA LOVE: 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…

This past April, at a conference on animal consciousness at New York University, a group of biologists and philosophers… released what they call the New York Declaration on Animal Consciousness. It argued that, based on current evidence, there is “at least a realistic possibility of conscious experience in all vertebrates . . . and many invertebrates,” including bees and fruit flies. SOURCE…

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