Squids And Other Invertebrates Can Probably Feel Pain

The ghost of calamari past...

Reef Squid

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Do animals without backbones, such as squids, crabs, and lobsters, feel pain? New research suggests they do.

Evolutionary neurobiologist Robyn Crook and colleagues at the University of Texas Health Science Center have recently shown that cephalopods (a group including squid and octopi) possess nociceptors, nerve cell endings that quickly transmit potentially-damaging stimuli to the central nervous system. Crook "also has found that octopuses show much of the pain-related behavior seen in vertebrates, such as grooming and protecting an injured body part," as New Scientist reported. The animals are also more likely to retreat and squirt ink when touched near a wound than elsewhere on their body.

Here's what's going on with squid:

Squids, though, may feel pain very differently. Shortly after a squid’s fin is crushed, nociceptors become active not only in the region of the wound but across a large part of its body, extending as far as the opposite fin. This suggests that if it feels pain, rather than being able to pinpoint the location of a wound, an injured squid may hurt all over. Crook is not certain why this would be. But it makes sense from a squid’s point of view, she says. Unlike an octopus, a squid’s tentacles can’t reach many parts of its body, so it couldn’t tend a wound even if it knew where the injury was.

This research compliments work done by Robert Elwood, a professor of animal behavior at Queen's University in Belfast, Northern Ireland, showing that crabs and lobsters probably feel pain:

If [Elwood] applied a brief electric shock to one part of a hermit crab, it would rub at that spot for extended periods with its claws. Brown crabs rubbed and picked at their wound when a claw was removed, as it is in fisheries. At times the prawns [young lobsters] and crabs would contort their limbs into awkward positions to reach the injury. “These are not just reflexes,” Elwood says. “This is prolonged and complicated behavior, which clearly involves the central nervous system."

The jury is still out on smaller invertebrates like insects. It's reasonable to think that if small crustaceans can feel pain, then so can some insects, which can have similar-sized nervous systems. But one researcher in this area, Hans Smid at Wageningen University in the Netherlands, said insects do not show pain-related behavior and he is convinced they do not feel pain.