Matthew Roy; Wikipedia

Every year thousands of them are boiled or torn apart while they are still alive, and now there is strong evidence to suggest that crustaceans experience pain.

That was the stark message delivered by Robert Elwood, an animal behaviour researcher at Queen’s University Belfast, to the Behaviour 2013 meeting in Newcastle, UK, today.

Crustaceans — crabs, prawns, lobsters and other creatures — are generally not protected by animal-welfare laws, despite huge numbers of them being caught or farmed for human consumption. The exclusion has been based on the belief that these animals cannot experience pain — generally regarded as an ‘unpleasant feeling’ — and instead only have nociception, a reflex response to move away from a noxious stimulus.

This is a useful belief, as crustaceans are subjected to what Elwood calls “extreme procedures” — lobsters in factories having their legs removed while they are still alive, crabs being kept alive but tightly bound for days in fish markets, and live prawns being impaled on sticks for eating. Such procedures, he notes, “would never be allowed with vertebrates”.

One way Elwood attempted to determine whether crustaceans can experience pain was to look at avoidance learning: can the animals actually learn from pain, or do they just continue to respond to a stimulus? To answer this, Elwood and his colleague Barry Magee presented shore crabs with a choice of two different shelters. Entering one shelter resulted in an electric shock for the animal, which was repeated if the animal remained there. The other shelter was a safe haven.

Crabs shocked the second time the experiment was run were far more likely to choose the other shelter in the next trial, while crabs never left a non-shocking shelter. This, says Elwood, shows that the shock is aversive.

In another experiment Elwood investigated whether hermit crabs could make motivational trade-offs as a result of pain. They presented Pagurus bernhardus crabs with two types of shell, one of which the animals are known to prefer, and gave some of the animals small electric shocks when they were inside these new homes.

When these crabs were later presented with a new shell they could move into, the shocked crabs were more likely to take up this offer, and they did so more quickly.

“Assessing pain is difficult, even within humans,” Elwood told the Newcastle meeting. But there is a “clear, long-term motivational change [in these experiments] that is entirely consistent with the idea of pain”.

Such evidence would be enough to prevent mice being subjected to the deaths that crustaceans experience, he says.

Robert Hubrecht, deputy director of the Universities Federation for Animal Welfare (UFAW) and the organizer of the session at which Elwood gave his talk, says that the data for crustaceans appear equivalent to the kind of data that are used to give mice the benefit of the doubt, and thus award them protection from possible pain under the law.

“We’re behaving in an illogical way at the moment” by protecting mice but not crustaceans, he notes.

Whether wider society is ready to consider crabs as things that can feel pain and should be protected is not clear. “This is somewhere science has to lead,” says Hubrecht.