Can invertebrates feel pain like we do? That’s a more philosophical question than you might think and as of yet, nobody knows for sure. What we do know is that physical injury does alter the behavior of squid.

Previous studies have suggested that after sustaining an injury, squid enter a heightened state of defensiveness – presumably to make up for the fact that part of their body has been compromised. What researchers wanted to find out more recently is how well this response works in actually avoiding death in a predator-prey scenario. To do this, a recent study published in Current Biology looked at squid which had been injured and able to sense the injury, as well as squid which were injured but were not able to sense an injury. What they found was that the squid who could sense the injury – and thus trigger the defensive response – were much better at avoiding predators. This could provide some interesting insight on our own reactions to injury, and whether or not there is a deep-rooted evolutionary purpose for the sensation us humans call pain.

“It’s long been thought that pain causes an animal to act self-protectively,” Robert Elwood told National Geographic. Elwood is an animal behavior researcher at Queen’s University Belfast (he was not involved in the study). “Pain teaches an organism to avoid situations that will bring it on. It seems obvious, but it hasn’t really been tested until now,” Elwood said in the email interview.

A school of longfin inshore squid, the species used for the experiments.

First the researchers induced a minor injury to longfin inshore squid by cutting off a tip of one of their arms. To make sure they were truly observing the effect of a post-injury sensation and not the mechanical effect of losing a body part, they injected some of the injured squid with local anesthesia that would knock out the sensation. They also set aside two groups of control squid – one with no injury and one with no injury but local anesthesia. Then came the bass. The predators used for the experiment were black sea bass who weren’t injured or anesthetized by anything, but merely very hungry for a species they dine on in the wild.

Presumably knowing what an easier meal looks like, the black sea bass seemed to show a strong preference for the injured squid, targeting them over the intact specimens. Not surprisingly, both of the injured groups had lower survival rates when attacked than the uninjured groups. However, of those two injured groups, about 45% of those who could feel that they were injured survived the attacks while less than 25% of the anesthetized squid survived.

Once animals have sustained an injury, “they’re at high risk of death and they need something to cope with it,” the study’s co-author Robyn Crook told National Geographic. “Their sensitive or hyperaware state post-injury seems to be that coping response.”

It’s unclear whether or not invertebrates truly feel pain in the way that we do, but is it possible that the irritability and hypersensitivity we feel after an injury represents the same evolutionary phenomenon apparent in these squid? “One of the effects of pain is the peripheral sensory system becomes hyperactive,” Edgar T. Walters told the Los Angeles Times. Walters was also a co-author of the study and researches pain and neural plasticity at the University of Texas Medical School at Houston. “People in pain are very easily irritated and we found that this fits in with a primitive pattern designed for an animal to be extra-vigilant.”

So next time you’re complaining about your sore back or aching neck – don’t feel like you’re being a whiner. Your body may just be making sure you don’t get attacked by a predator, be it a black sea bass or something slightly more intimidating.

HT: Current Biology, National Geographic, Los Angeles Time

IMAGES: Squid komodo by Nhobgood

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