Everybody Hurts (Even Crabs)

When I'm not blogging for mental_floss, I can usually be found wearing bright orange rubber pants and gutting,cutting and selling fish at my local Whole Foods (and winning awards for it). Sometimes, my two worlds collide and I find some scientific research involving my ocean-dwelling friends that begs for a blog post. This is one of those times.

Crabs + Old Bay seasoning + corn on the cob + potatoes + giant pot of boiling water = good times! It's an equation elegant in its simplicity, unhindered by complications (and formalities like shirts and socks) until—inevitably—a dining partner wonders aloud, "Do you think the crabs feel pain?"

The answer, according to a new study published in Animal Behavior,¹ is that not only can they can feel pain, they remember it, and use the experience to avoid pain in the future.²

Shell Shocked

Robert Elwood and Mirjam Appel, both of the School of Biological Sciences at The Queen's University in Belfast, conducted two experiments with hermit crabs (Pagurus bernhardus) collected from rock pools in County Down, Northern Ireland.³ Hermit crabs, having no shells of their own, often take up residence in empty gastropod shells. In the first experiment, the researchers attached wires to some empty shells and used them to deliver small electric shocks to the crabs who attempted to make the shells their home. They found that the crabs who received shocks quickly abandoned their shells; the crabs who weren't shocked stayed in their shells, with fewer crabs abandoning species of shell that hermit crabs generally prefer. "The abandonment of this critical resource [the shell]," the researchers say, "clearly demonstrates the aversive nature of the shock."

In the second part of the study, the researchers delivered shocks just slightly weaker than the strength needed to cause a crab to instantly vacate its shell. The slightly-less-shocked crabs, as well as those spared a shock, were then offered new, unwired homes in additional empty shells placed close by. Those who had been shocked were more likely to approach and take up residence in the new shells than their unshocked brethren. They also "approached that shell more quickly, investigated it for a shorter time" and "poked around the shell's opening less prior to moving in."

Pain is a survival mechanism; it makes an individual aware of potential bodily damage and provides motivation to get away from painful stimuli and avoid them in the future. Previous studies showed that crabs can detect and retreat from harmful stimuli, but it was unclear if that behavior were a reflex or if it were connected to "feeling pain" as we humans understand it. Elwood and Appel say that, in their second experiment, the crabs' response was not simply a reflex, but that central neuronal processing was taking place.⁴ Because they did not offer the new shells until after some of the crabs were shocked, the shocked crabs' eagerness to move into the new shells appears to be motivated by the memory of the unpleasant shock and not reflex.

What's a crab lover to do?

There's no small amount of conflicting evidence for which method for killing crustaceans is most humane. Alton Brown's preferred technique for dispatching lobsters is stabbing a large chef's knife through the lobster's head just behind its eyes and moving the knife down, essentially bisecting its brain with one cut. While this method has its detractors, I tend to give Brown the final say on all things culinary (and otherwise), so it's good enough for me (though I was not prepared for the post-mortem wriggling) and can be adapted to crabs.

1Elwood, R; Appel, M. (2009). Pain experience in hermit crabs? Animal Behaviour 77 (5): 1243-46. doi:10.1016/j.anbehav.2009.01.028. 2The study defines pain as "the associated unpleasant, emotional interpretation or feeling" associated with the perception of "a noxious, potentially tissue-damaging, stimulus." 3 All crabs used in the experiments survived and were subsequently given suitable new shells and released into their native habitat. 4 Our emotional experience of pain, what one might call suffering, happens in the neocortex, a complex and very wrinkly region of the brain involved in higher functions, like conscious thought and language. In this region, neurons devoted specifically to pain impulses process neural messages from the pain receptors throughout our bodies. Without a neocortex, one would assume, an individual could not experience pain, but it turns out that crustaceans' nervous systems are wired a little differently than our own: they lack the visual cortex than humans have, but can still see. So can crustaceans suffer without what we believe to be the requisite parts? In his well-known 2004 Gourmet article "Consider the Lobster," David Foster Wallace* wrote that "comparative neuroanatomy is only part of the problem. Since pain is a totally subjective mental experience, we do not have direct access to anyone or anything's pain but our own"¦The fact that even the most highly evolved nonhuman mammals can't use language to communicate with us about their subjective mental experience is only the first layer of additional complication in trying to extend our reasoning about pain and morality to animals." However, in another study awaiting publication in Applied Animal Behavior Science, Elwood and his colleagues put forth seven reasons, with research-based support, that they believe crustaceans suffer: "a suitable central nervous system and receptors," the fact that they learn to avoid negative stimuli, engagement in protective reactions like limping and rubbing, physiological changes like release of adrenal-like hormones, decisions based on past likely painful events, fewer responses to negative stimuli after receiving anesthetics and "high cognitive ability and sentience." * Whom I guess I'm sort of channeling with all these footnotes. Maybe I should go get a bandana.