Insects May Be Able to Feel Pain, Study Suggests

The question of whether or not insects feel pain is a matter of heated debate among scientists.

In a study published on Tuesday, a team of researchers argue that these animals have a certain biological mechanism that indicates they may indeed have a subjective experience of pain.

In the paper, published in the journal Proceedings of the Royal Society B: Biological Sciences, the researchers reviewed a range of scientific evidence and came to the conclusion that insects most likely have central nervous system control of something called nociception (the detection of potentially or actually damaging stimuli) and that this is consistent with the existence of a pain experience.

According to the lead author of the paper, Matilda Gibbons from the School of Biological and Behavioural Sciences at Queen Mary University of London (QMUL) in the U.K., nociception typically results in reflex-like responses such as rapid withdrawal or escape from harmful stimuli.

Nociception can be accompanied by the feeling of pain, which is a negative subjective experience produced by the brain, although this is not always the case.

A dead cockroach
A file photo of a dead cockroach on a kitchen floor. Are insects capable of feeling pain? iStock

"Such reflexes exist even in relatively simple animals such as worms and might not necessarily be accompanied by a subjective experience of pain or suffering," Gibbons told Newsweek. "But how does one assess the likelihood of pain in an animal, in contrast to basic nociception?"

While basic nociception has been well-documented in insects, it has not been established that these animals have the ability to control (or "modulate") nociception—a characteristic of creatures like humans that do have a subjective experience of pain.

In mammals, for example, this ability—which scientists call "the descending control of nociception"—is executed by neurons in the brain. This ability provides an important adaptive function, enabling an animal to adjust its behavior in different contexts in order to prioritize survival.

"For example, if an animal is injured during a fight, the dampening of their nociceptive processing may increase the animal's fighting performance by ensuring they do not waste time or energy on responding to the injury," the authors wrote in their study.

But whether or not insects have such control or even the neural circuits required for it has rarely been investigated.

"One hallmark of human pain perception is that it can be modulated by nerve signals from the brain," Gibbons said. "Soldiers are sometimes oblivious to serious injuries in the battlefield since the body's own opiates suppress the nociceptive signal."

"You can also consciously 'grit your teeth' and bear the pain, in case such 'heroic' behavior earns you a reward or prestige," she said. "We thus asked if the insect brain contains the nerve mechanisms that would make the experience of a pain-like perception plausible, rather than just basic nociception."

Adapting Like Humans

After reviewing a range of neurobiological and behavioural evidence, the authors found that insects likely do have a neural system for dampening their their responses to potentially-painful stimuli so they can adapt their behavior flexibly to different contexts, just as humans do.

"The function of this dampening in nociception in humans is to reduce our pain in situations where feeling pain is unhelpful," Gibbons said. "Thus if insects also have this capacity, it is conceivable that insects have evolved a similar pathway to deal with feelings of pain."

Given that there is no direct way to measure the subjective experience of pain in any animal, the conclusions of the latest paper are significant, the authors said.

"We cannot ask these animals about their experiences, nor can we observe manifestations like wincing or facial contortions, as we might in a dog who experiences pain, so the existence of neural mechanisms that might mediate pain in insects is an important finding," Gibbons said.

Lars Chittka, another author of the study from QMUL told Newsweek that, to the best of his knowledge, this is the first paper to draw all the lines of evidence together to reach this conclusion—one which could have significant implications from an ethical perspective.

"The presence of brain controls for nociception is important because [it] makes it at least plausible that insects have painful experiences," said Chittka, who is also an author of the book The Mind of a Bee. "Descending control of nociception in humans can also affect pain perception, so it could be argued that pain is also affected in non-verbal animals."

"This is certainly the accepted argument for mammals such as mice, where a reduction in nociceptive behaviour is accepted as equalling a reduction in pain," he said. "This is important in terms of ethics, as insects are subjected to potentially-painful stimuli in research and farming."

The latest study comes at a time when public perception and legislation regarding other invertebrates (animals without a backbone) is beginning to change. Some governments, for example, have recognized that animals like lobsters, octopuses and crabs are sentient beings capable of experiencing pain or suffering.

"We stand at an important crossroads in terms of how to feed a human population that is projected to reach 10 billion people by 2050, while conventional livestock farming aggravates climate change on a grand scale," Sajedeh Sarlak, an author of the study from the University of Tehran, Iran, told Newsweek.

"The United Nations therefore recommend to move from traditional livestock to mass-production of insects for food. In line with this, the commercial rearing of various insect species for human consumption is a rapidly growing sector in many parts of the world."

"But the ethical implications have so far not been considered, in part because many decision-makers' view is that there are none to consider for insects," Sarlak said. "We need to understand: are insects capable of the experiences of pain and suffering, to ensure that the ethical mistakes of conventional battery livestock farming are not repeated."