Boiling lobsters alive for food must stop, say scientists, who say their experiments show that, along with other crustaceans such as crabs and prawns they do feel pain.
Some researchers have suggested that when such creatures avoid a painful stimulus it's actually because of a phenomenon known as nociception: a reflex response to move away.
A team at Queen's University Belfast has now attempted to solve the mystery by distinguishing between nocioreception - which has only a short-term effect - and pain itself. They looked at the reactions of common shore crabs to small electrical shocks, and their behaviour afterwards.
"The experiment was carefully designed to distinguish between pain and a reflex phenomenon known as nociception. The function of pain is to aid future avoidance of the pain source, whereas nociception enables a reflex response that provides immediate protection but no awareness or changes to long-term behaviour," says Professor Bob Elwood.
"While nociception is generally accepted to exist in virtually all animals, the same is not true of pain. In particular, whether or not crustaceans experience pain remains widely debated."
The team discovered that shore crabs were willing to trade something of value to them – a dark shelter – in order to avoid future electric shock. Ninety crabs were each introduced individually to a tank with two dark shelters. On selecting their shelter of choice, some were exposed to an electric shock the first two times they visited it.
"When introduced to the tank for the third time, however, the vast majority of shocked crabs now went to the alternative safe shelter. Those not shocked continued to use their preferred shelter," says Elwood.
"Having experienced two rounds of shocks, the crabs learned to avoid the shelter where they received the shock. They were willing to give up their hideaway in order to avoid the source of their probable pain."
Elwood says that the food industry should re-evaluate how such creatures are treated.
"In contrast to mammals, crustaceans are given little or no protection as the presumption is that they cannot experience pain. Our research suggests otherwise," he says.
"More consideration of the treatment of these animals is needed as a potentially very large problem is being ignored."