Do a Google news search for “lobster” and “pain” and you will come up with a list of conflicting news articles such as “Lobsters and Crabs Feel Pain, Study Shows” and “Scientists Say Lobsters Feel No Pain”. Its a hot debate, the research and reporting on crustacean nociception and pain is mixed and complex, there just is no simple scientific consensus on the issue. While researching the subject I stumbled across this blog post in which the author rightly debunks the myth that lobsters scream when boiled, the sound is actually hot air escaping through their carapace. But the author then asserts that lobsters and other crustaceans also simply do not have the necessary “nerve pathways and brain regions” to feel pain. The author goes on to say that “…they don’t have a real brain at all, for that matter. In other words, no brain, no pain”. While there is legitimate contention about the degree to which crustaceans are sentient or can feel pain, the idea that lobsters (and other crustaceans) do not posses a brain or endogenous opioid receptors is simply false. I’m not sure where the author was getting their information, perhaps it was this 2005 CNN article, which uses the “No brain, no pain” phrasing, about a report on lobsters in which scientists at the University of Oslo state “it is unlikely that they can feel pain.” But it was far from conclusive, the scientists themselves wrote near the end of their report,
“Still, it is not clear if the lobster can feel pain…we may be mistaken in assuming that invertebrates have a reduced capacity to experience suffering. Suffering is a private experience, or a negative mental state that cannot be measured directly. The responses of invertebrates to noxious conditions are often strikingly similar to those of vertebrates. Several experimental studies have shown that invertebrates such as cockroaches, flies and slugs have short and long-term memory, have ability of spatial and social learning, perform appropriately on preference tests, and may exhibit behavioural and physiological responses indicative of pain. The similarity of these responses to those of vertebrates may indicate a level of consciousness or suffering that is normally not attributed to invertebrates.” and added “there is apparently a paucity of exact knowledge on sentience in crustaceans, and more research is needed”
In commenting on the 2005 CNN article and the “No brain, no pain” meme, one Associate Professor of Biology who specializes in crustacean neurobiology at The University of Texas-Pan American wrote, “I won’t comment on the pain portion, but as to the claim that a lobster has no brain? It is wrong. It is false. It is incorrect. It is untrue. I don’t know how much more flatly I can say it. Lobsters have brains. So do crabs and crayfish and other crustaceans”
There have been numerous studies relevant to crustacean nociception, pain, and sentience but they have had mixed results, some of the positive studies made conclusions such as “We conclude that there is considerable similarity of function, although different systems are used, and thus there might be a similar experience in terms of suffering.“, “The results are consistent with the idea of pain in these animals.“, and “These findings are consistent with the idea of a pain experience rather than a nociceptive reflex.” A 2009 review of the published evidence lead one researcher to write
“A number of studies, although not specifically directed to the issue of pain, shows the ability of crustacean decapods to display such a rich behavioural repertoire that, if exhibited by vertebrates, would have been considered to be indicative of higher mental faculties. Again, the underlying rationale is that animals that possess such behaviours are sentient and may experience pain. Understandably, complexity in behaviour does not indicate consciousness but it may set out the basis for it”.
One study published in Animal Behavior in 2008, showed that when acetic acid was applied to the antenna of prawns that they would groom the afflicted antenna and rub it on the side of the tank. Benzocaine, a local anesthetic, was found to inhibit this grooming and rubbing response without altering their general swimming activity. The researchers concluded, “The inhibition by a local anaesthetic is similar to observations on vertebrates and is consistent with the idea that these crustaceans can experience pain.”
On the other hand a similar study from 2010, looking at different species than the 2008 study, found “no change in behaviour… compared to controls“, concluding that, “previously reported responses to extreme pH are either not consistently evoked across species or were mischaracterized as nociception. There was no behavioural or physiological evidence that the antennae contained specialized nociceptors that responded to pH.” Unfortunately the nuance was lost on many and the author felt the need to clarify by pointing out on their blog a critical point from the paper, “we are not claiming that crustaceans do not have nociceptors. We are not claiming that crustaceans do not feel pain. Indeed, as we have emphasized, there are many reasons to expect that they could, making the results presented here all the more surprising.”
Similarly, experiments looking at changes in defensive behavior after administering injections of morphine and naloxone to crabs has yielded mixed results (1, 2, 3). Other evidence seems to demonstrates that crustaceans also may not be merely mindless automatons but rather posses some degree of agency, i.e. the ability to act outside of unconscious reaction & instinct. All that being said, pain is only one aspect of sentience and we should also be aware that different species cant develop widely different capacities and ways of interacting with the world. We also must be wary of being anthropocentric or vertebracentric (as some have called it) by only making direct comparisons to vertebrate physiology which are not always appropriate since nerves and brain regions can be co-opted for different purposes among different species.
So what does this all mean? We are left in the position of making an educated guess. We have to weigh the evidence and consider the potential ethical ramifications. Most of all we must learn to become comfortable with a degree of uncertainty. But even without perfect evidence we eventually need to make the decision of whether we will eat lobster and crab or not. To me, evidence of the possibility of some form of sentience in crustaceans and the potential costs of imposing suffering and ending an experience of life are just too great to ignore. I think Peter Singer had it right when he wrote,
“If crustacea can suffer, there must be a great deal of suffering involved, not only in the method by which they are killed, but also in the ways in which they are transported and kept alive at markets. To keep them fresh they are frequently simply packed, alive, on top of each other. So even if there is some room for doubt about the capacity of these animals to feel pain, the fact that they may be suffering a great deal, combined with the absence of any need to eat them on our part, makes the verdict plain: they should receive the benefit of the doubt.“
Update 1/21/13: A new study titled, Shock avoidance by discrimination learning in the shore crab (Carcinus maenas) is consistent with a key criterion for pain adds another data point and concludes,
These data, and those of other recent experiments, are consistent with key criteria for pain experience and are broadly similar to those from vertebrate studies.