Figuring out whether an animal feels pain or not is a pretty difficult task. You can’t exactly go and ask them, and judging by their reactions also isn’t clear. Most animals (if not all) exhibit something called nociception — a physical reaction to harm that is useful (it helps the animal avoid what is harmful) — but this is not exactly pain per se.

Until not very long ago, it was thought that only humans and some mammals can feel pain. Increasingly, though, researchers found out that way more animals can feel pain. Fish are one good example: for a long time, we thought fish couldn’t feel pain, but research has shown that that’s not really the case. Now, it’s time for the insects to go under the magnifying glass.

Behaviorally, insects are very tough to study. They’re small, it’s hard to communicate with them, and they’re nothing like us. But a team of researchers found that insects do respond to very severe physical damage, like when one of their legs is cut, for instance. But this doesn’t really say anything about whether this response is nociception or actual pain. So far, nothing new.

To look at the matter more deeply, the team started straight from the source: the insects’ nervous systems. They started by drawing comparisons with humans. When humans undergo an emergency (say, a car crash), they may be injured and not even realize it until much later. This is because sometimes, in an emergency, the brain produces opiates that hijack the brain and prevent it from feeling pain.

Insects don’t really produce opiates, but they produce neuropeptides, which are substances that serve a similar purpose. Researchers found that when insects were exposed to physical trauma, they seem to produce neuropeptides, mimicking how humans and other vertebrates produce opiates, which is possible evidence of them feeling pain.

This isn’t the first time researchers have found evidence of feeling pain. In 2019, one study showed that insects can experience chronic pain and, increasingly, evidence is mounting that insects may be more sentient than we thought.

Ultimately, the researchers argue that while more research is needed to investigate this, there are striking similarities between how vertebrates and insects react to pain. But studying this in more detail brings up a new challenge: if insects can feel pain, then there are ethical considerations as to how you can study and inflict that pain on them.

Journal Reference: Matilda Gibbons et al, Descending control of nociception in insects?, Proceedings of the Royal Society B: Biological Sciences (2022). DOI: 10.1098/rspb.2022.0599