Wires were attached to shells to deliver the small shocks to the abdomen of the some of the crabs within the shells.
The only crabs to get out of their shells were those which had received shocks, indicating that the experience is unpleasant for them. This shows that central neuronal processing occurs rather than the response merely being a reflex.
Crabs that had been shocked but had remained in their shell appeared to remember the experience of the shock because they quickly moved towards the new shell, investigated it briefly and were more likely to change to the new shell compared to those that had not been shocked.
Professor Elwood said: "There has been a long debate about whether crustaceans including crabs, prawns and lobsters feel pain.
"We know from previous research that they can detect harmful stimuli and withdraw from the source of the stimuli 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.
"Such trade-offs are seen in vertebrates in which the response to pain is controlled with respect to other requirements.
From the Upcoming ueue, submitted by Geekazoid.
The question isn't "can they feel pain"?, it's "Do they remember feeling pain, and avoid being in that situation again in which they did?"
This article seems to imply that the hermit crabs are able to sense an irritant and find a new home, not that they feel any pain. I've watched my own hermits climb out of their shells, turn and shake sand out of them, then scoot right back into them. I've even seen starve themselves to death if they're unable to find a suitable new home.
Hollywood Bob hit upon it. The neurology is different. They don't feel it like we would, for example. They probably sense that something isn't right, but then just die.
As for crabs, the easiest and fastest way to kill them is to basically cut them straight in half. There isn't even any residual nerve movement afterward.
And let's face it, even if they were screaming bloody murder, they are too tasty and nutritious for me to care.
For anyone curious about the ethics and science of lobster-eating, I'd recommend the inimitable David Foster Wallaces' "Consider the Lobster:"
http://www.lobsterlib.com/feat/davidwallace/page/lobsterarticle.pdf
Creatures suffer, what can you do? Starve? Go vegan? But there again, plants are living things too. Humans don't photosynthesize, we have to consume other living things to survive. I'll shed a tear over the next crab i eat, someone pass the butter please.