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Hurting an insect may force it to live in agony for the rest of its life

Published Jul 16th, 2019 8:53PM EDT
do insects feel pain
Image: B Borrell Casals/Flpa/imageBROKER/Shutterstock

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If your first instinct upon noticing a pesky fly buzzing around your person is to swat at it in the hopes of sending it elsewhere or even killing it, well, you’re pretty normal. We don’t often think twice when it comes to dispatching insects we find in our homes or even ones that get too close when spending time outdoors, but a new study published in Science Advances suggests that failing to kill an insect and merely injuring it may cause it to live the rest of its days in agony.

It’s tempting to imagine that life forms like insects don’t “feel” pain, thereby absolving us from any guilt we might feel in slapping a fly or stepping on an ant, but that way of thinking isn’t entirely accurate.

Scientists have known for a while that even less-complex organisms like insects have the ability to sense potentially dangerous stimuli, including physical injuries. It’s called nociception, and while it’s slightly different than how humans process pain, it’s actually not that far off.

What researchers didn’t necessarily know before this latest round of research was whether or not injuries to insects produce what we think of as chronic pain, or pain that persists long after a physical injury has occurred. As it turns out, they do.

In a series of tests, fruit flies had legs amputated in a laboratory setting. The wounds were given time to heal, at which point the scientists continued the experiment by exposing the flies to various stimuli. The flies, like other animals and even humans, appeared to be far more sensitive to possible sources of new pain after being previously injured.

“The fly is 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. In this nerve cord are inhibitory neurons that act like a ‘gate’ to allow or block pain perception based on the context,” Associate Professor Greg Neely of the University of Sydney, lead author of the work, explains. “After the injury, the injured nerve dumps all its cargo in the nerve cord and kills all the brakes, forever. Then the rest of the animal doesn’t have brakes on its ‘pain’. The ‘pain’ threshold changes and now they are hypervigilant.”

The researchers suggest that this may be the insect version of “chronic pain,” where injuries promote hyper-sensitivity and lower the overall pain threshold. In flies, it could keep them safe from further dangers, but in humans it just makes us feel like junk.

“Importantly now we know the critical step causing neuropathic ‘pain’ in flies, mice and probably humans, is the loss of the pain brakes in the central nervous system, we are focused on making new stem cell therapies or drugs that target the underlying cause and stop pain for good,” Neely said.

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