Bugs Experience Chronic Pain, Too

Like humans, drunken fruit flies feel like they're ready for lift-off... at first. Cornel Constantin/Shutterstock

Ever wonder why bugs run like their very lives depend on it when you discover their secret lair?

Maybe it's because more times than not, we go full Godzilla on them. Who wants to stick around to get stomped in the most gruesome way possible?

Humans often shriek and make all sorts of terrible bellowings while crushing insects to bits. Some people even exalt in the carnage — strangely satisfied with the imprint a squished centipede makes on the wall. And still twitching slightly!

Yes, bugs have every reason to run. Especially since they probably do feel the boot coming down on them.

"People don't really think of insects as feeling any kind of pain," Greg Neely, a professor at the University of Sydney, explains in a press release. "But it's already been shown in lots of different invertebrate animals that they can sense and avoid dangerous stimuli that we perceive as painful."

It's a little more complicated than the ouch accompanying a stubbed human toe.

Scientists call bug-pain "nociception" — a biological aversion to harmful stimuli like heat, cold ... or squishing. But many insects are troopers — we're looking at you, nearly invincible cockroach — and keep trucking after losing the occasional leg or antenna. They might even heal completely.

But a newly published study led by Neely suggests insects can live their whole lives with chronic pain. For the study, Neely's team looked at the tiniest of victims — Drosophila, also known as fruit flies.

For the first time, they found genetic evidence of what causes chronic pain in fruit flies, and suggest it may be the same mechanism that drives chronic pain in humans.

"So we knew that insects could sense 'pain'," Neely explains. "But what we didn't know is that an injury could lead to long lasting hypersensitivity to normally non-painful stimuli in a similar way to human patients' experiences."

So a half-swatted fruit fly may appear to have made a full recovery from its efforts to eat your banana, but it will likely live with persistent pain for a very long time. Or at least, for the 40 to 50 days a fruit fly actually lives.

Fruit flies gathered on a banana
A fruit fly risks a terrible death when it competes with humans for food. UPAPORNKH/Shutterstock

For the study, researchers conducted a series of experiments, including damaging nerves in a fruit fly's leg. They let the injury fully heal, but noted that the subject's other legs had become hypersensitive.

"After the animal is hurt once badly, they are hypersensitive and try to protect themselves for the rest of their lives," Neely notes. "That's kind of cool and intuitive."

Then — and with apologies to the hapless fruit fly — came the dissection.

Dismantling the insect revealed it was "receiving 'pain' messages from its body that then go through sensory neurons to the ventral nerve cord, the fly's version of our spinal cord," Neely explains.

"In this nerve cord are inhibitory neurons that act like a 'gate' to allow or block pain perception based on the context."

But where there's pain, there's scientific gain. The researchers say by tapping into the mechanisms behind bug suffering — specifically those neurons that act as "pain brakes" — they may be able to turn off chronic pain in humans.

"If we can develop drugs or new stem cell therapies that can target and repair the underlying cause, instead of the symptoms, this might help a lot of people," Neely adds.

The idea is to wean humans off opioids as a form of pain treatment, a double-edged sword that both dulls pain and fuels addiction.

"Animals need to lose the 'pain' brakes to survive in dangerous situations, but when humans lose those brakes it makes our lives miserable," Neely says. "We need to get the brakes back to live a comfortable and non-painful existence."