Hermit crabs can remember pain

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As well as experiencing pain, crabs also remember it, according to new research.

The study, carried out on at Queen s University, Belfast, by Professor Bob Elwood and Mirjam Appel, used small electric shocks to test for reactions in hermit crabs.

Not only were the crabs found to react adversely to the electric shocks, but the study " published in the journal Animal Behaviour " also suggests that the crabs would actively avoid receiving future shocks.

One group of hermit crabs, Pagurus bernhardus, were given electric shocks just below threshold level within their shell, while a second group of the hermit crabs were not shocked.

The researchers observed that during this shocking period, the only hermit crabs to evacuate their shells were in the group that received a shock. Some of these crabs were even observed to attack the shell they evacuated.

Following the shocks, all of the crabs in the study were offered a new shell. It was found that those hermit crabs that had been given a shock were more likely to switch from their current shell than those that had not.

In addition, the crabs that received the shock spent less time exploring the new shell before making the switching " indicating that they were more like to make that switch even if the new shell on offer was inferior to their current one.

We know from previous research that they can detect harmful stimuli and withdraw from the source of the stimuli, Professor Elwood told the BBC. But that could be a simple reflex without the inner 'feeling' of unpleasantness that we associate with pain.

This research demonstrates that it is not a simple reflex, but that crabs trade-off their need for a quality shell with the need to avoid the harmful stimulus.

Trade-offs of this type have not been previously demonstrated in crustaceans. The results are consistent with the idea of pain being experienced by these animals.

For more information see the paper: Elwood, R.W., Appel, M. 2009. ~Pain experience in hermit crabs? Animal Behaviour, doi:10.1016/j.anbehav.2009.01.028