Researchers test the behavioral responses of octopuses to touches of increasing force on different body areas. This helps distinguish behaviors that are simple nociceptive reflexes from those that could indicate pain. (Robyn Crook, University of Texas/Jean Alupay, UC Berkeley/Stavros Hadjisolomou, CUNY Brooklyn)


Robert Elwood had been working with crabs and prawns for the better part of three decades when Rick Stein confronted him with this question in a pub on the coast of Northern Ireland. Elwood was stumped. “It was the first time I ever considered the question,” he says.

Although some people are horrified by the idea of cooking lobsters alive or the practice of tearing claws from live crabs before tossing them back into the sea, such views are based on a hunch. We know very little about whether these animals — or invertebrates in general — actually suffer. In Elwood’s experience, researchers are either certain the animals feel pain or certain they don’t. “Very few people say we need to know,” he says.

The global food industry farms or catches billions of invertebrates every year. But unlike their vertebrate cousins, they have virtually no legal protection. “Early on in my career I realized that when the law speaks of animals, it does not mean invertebrates,” says Antoine Goetschel, an international animal law and ethics consultant based in Zurich. “As long as the common opinion is that invertebrates do not suffer, they are out of the game.”

Pain vs. reflex

Pain is an awkward thing to test. It can’t be measured directly or pointed at; it’s not even easy to define. How can we tell when an animal is suffering? We have come a long way since Descartes, who argued that all non-human animals were merely automata, without self-awareness and incapable of feeling. But much of what we think we know still involves a lot of guesswork.

Some people are horrified by the idea of cooking lobsters alive or the practice of tearing claws from live crabs before tossing them back into the sea. (Brian Snyder/Reuters)

So how do we answer Stein’s question? Elwood has been looking for ways to do so since running into Stein eight years ago. For a start, arguments by analogy are silly, he says. “Denying that crabs feel pain because they don’t have the same biology is like denying they can see because they don’t have a visual cortex.”

Elwood and his colleagues at Queen’s University Belfast are instead tackling the question by looking at how these animals behave. Most organisms can respond to a stimulus that signals a potentially harmful event. Special receptors called nociceptors — which sense excessive temperatures, noxious chemicals or mechanical injuries such as crushing or tearing — are found throughout the animal world, from humans to fruit flies. When a parasitic wasp jabs its egg-laying ovipositor into a fruit fly larva, for example, the larva senses the needle and curls up, which can make the wasp pull out.



He then turned to crabs. If he 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 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.”

He investigated further by placing shore crabs in a brightly lit tank with two shelters. Shore crabs prefer to hide under rocks during the day, so in this situation they should pick a shelter and stay there. But giving some of the crabs a shock inside one of the shelters forced them to venture outside. After only two trials, the crabs that had received shocks were far more likely to switch their choice of shelter. “So there is rapid learning,” Elwood says, “just what you would expect to see from an animal that experienced pain.”



The squid question

And it is not just crustaceans. Robyn Crook, an evolutionary neurobiologist at the University of Texas Health Science Center in Houston, is asking many of the same questions of cephalopods, such as squids and octopuses. “We are learning things we never expected to find,” she says.


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. Squids also have a fast metabolism that forces them to stay on the move and keep hunting. An all-over heightened sensitivity may keep a squid generally more alert and wary. For example, Crook has found that an injured squid will be more sensitive than others to touch and visual stimuli. “Its long-term behavior changes,” she says. “This fulfils one important criterion for pain.”

If not the backbone . . .



Hans Smid, who studies the brains and learning behavior of parasitic wasps at Wageningen University in the Netherlands, dismisses the possibility. “I am absolutely convinced that insects do not feel pain,” he says.



No gain, no pain

In terms of relative brain size, fruit flies and the parasitic wasps that Smid studies are the masterminds of the insect world. But neurons consume a lot of energy, and there is evolutionary pressure to keep brains as compact as possible. In short, there need to be good reasons to have enough brain for pain. Smid thinks that insects simply do not have the need. “I don’t see the evolutionary advantage for insects to sustain such a complex system as emotion, of which pain would be just one component,” he says.

Elwood agrees this is a useful way to frame the question. “From an evolutionary perspective, the only reason for pain that makes sense to me is that it enables long-term protection,” he says. Pain may provide an animal with an additional, and memorable, means of focusing on a source of harm that helps it avoid it in future. If an animal’s life span is not long enough to benefit from that — as is the case with most insects — then pain has no use. Similarly, some animals may simply be unable to avoid noxious stimuli in the first place. “Is a barnacle going to benefit from a bad experience?” Elwood says. “I doubt it.”


There are signs of change, too: Cephalopods at least now get some protection, in some parts of the world. “We are broadening our understanding of both pain and nociception,” Crook says. “How can this not be interesting, even to the skeptics?”

This article was produced by New Scientist.