A scientist and a seafood chef walk into a bar. “We have a mutual interest,” says the scientist. “I study crustaceans and you cook them.” But the chef wanted to know just one thing: Do the animals feel pain?
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 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.
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.
But when an animal responds to something we would consider painful, it does not necessarily mean the animal is in pain. The response might be a simple reflex, where signals do not travel all the way to the brain, bypassing the parts of the nervous system connected with the conscious perception of pain. When we scald our hand, for example, we immediately — and involuntarily — pull it away. Pain is the conscious experience that follows, once the signals have reached the brain. The key for Elwood was to look for responses that went beyond reflex, the crustacean equivalents of limping or nursing a wound.
He started with prawns. After so many years of working with them, he thought he knew what to expect, which was that he would see nothing more than reflex reactions. But to his surprise, when he brushed acetic acid on their antennae, they began grooming the treated antennae with complex, prolonged movements of both front legs. What’s more, the grooming diminished when local anesthetic was applied beforehand.
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.”
Finally, Elwood looked at how the need to escape pain competed with other desires. For humans, pain is a powerful motivational driver, and we go to great lengths to avoid it. But we also can override our instincts and choose to endure it if the rewards are great enough. We suffer the dentist’s drill for the long-term benefit, for example. What would a crustacean want badly enough to make it endure pain?
For hermit crabs, it turns out to be a good home. These animals take up residence in abandoned seashells, but they can be made to give up their home if given a shock inside the shell. Elwood found that the likelihood of a hermit crab’s dumping its shell when given a shock depends not only on the intensity of the shock but also on the desirability of the shell. Crabs in better shells took bigger shocks before they were willing to move out. This suggests that the crabs are able to weigh different needs when responding to the noxious stimulus. Once again, this behavior goes far beyond reflex, Elwood says.
(The Washington Post)
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