Do Crabs And Lobsters Feel Pain?
Download our full scientific briefing to the Government here:
It is commonly believed that crustaceans do not feel pain; that any responses to the pot or to the knife are mere 'reflex'. Scientific evidence shows that view to be misinformed and based more on species prejudice than on fact. Indeed, all decapod crustaceans, from lobsters to prawns, have been listed in European animal welfare guidelines since 2005 as Category 1 animals, where:
“The scientific evidence clearly indicates, either directly or by analogy with animals in the same taxonomic groups, that animals in those groups are able to experience pain and distress”.
There is ample evidence that crabs, lobsters and prawns are sentient and likely to be capable of feeling pain and experiencing suffering. They should therefore be protected under the criteria of the Animal Welfare Act. The experiments below received significant UK media interest in 2012 with many asking if our treatment of them should improve. Since that time, however, little has changed in industry practice.
Think that's unacceptable? Think there's more to animal welfare than a pretty face?
Understanding Pain In Non-Human Animals
Crustaceans have taken a very different evolutionary path to vertebrates, and their physiology is very different. However, this is not in itself evidence of absence of mechanisms for pain.
It is very difficult to prove the existence of a feeling of pain beyond doubt (even in humans). It can only be inferred through a variety of means. For example, by:
Looking at animals’ biology for structures and chemicals associated with pain-processing
Observing the way an animal responds to 'painful' stimuli
Administering 'pain' and then comparing behaviour before and after pain-relief is given
Exploring whether animals learn to avoid 'painful' stimuli, suggesting they have remembered the feeling
Exploring how far animals are prepared to ‘trade-off’ things that are valuable to them to avoid 'pain'
A number of scientists have examined the evidence for pain in crustaceans and found compelling evidence in their favour (see our scientific briefing). However, the strongest evidence yet that crustaceans feel pain has been presented by Professor Robert Elwood and his colleagues from Queens University Belfast. In 2012, they conducted a study to observe whether European shore crabs would not only respond to a painful stimulus (which could be mere reflex) but that they would actually experience it.
You can listen to Prof Elwood talk to BBC Radio 5 about his research and the implications below:
NOTE: The experiments below suggest that some pain is inflicted on the animals concerned, though the author stresses this was minimal and the animals returned to the shore. Crustacean Compassion believes that such research is essential to demonstrate welfare needs. However, we hope that future research will move as swiftly as possible beyond the establishment of painful sensations to explore other capacities and experiences.
The Shore Crab Shock Experiment (2)
European shore crabs usually find a dark, safe place to hide under rocks at low tide. For this experiment, a group of crabs were placed in a brightly lit tank with two shelters in which to hide. When placed into the tanks, all the crabs scuttled into the dark shelters. However, a randomised group of crabs were given a small electric shock every 5 seconds upon entry. The others, the control group, were left alone.
Following the shock, all the crabs were removed, and then replaced back into the same tanks. The crabs who had been shocked the first time were shocked again.
From round two of ten rounds, the shocked group of crabs became much more likely than the control group to switch shelters, demonstrating that they had learned to avoid the aversive experience. Thus it can be inferred that they had laid down memories and experienced the shock as unpleasant enough to trade the valuable commodity (a dark shelter) for a bright but shock-free tank. Professor Elwood stated
"I don't know what goes on in a crab's mind.... but what I can say is the whole behaviour goes beyond a straightforward reflex response and it fits all the criteria of pain." (3)
The Hermit Crab Motivational Trade-off Experiment (4)
One way of testing if crustacean’s responses to negative situations or events are a result of pain or are a reflex is to provide the animal with a way to avoid the stimulus, but to vary the potential cost of avoidance. If avoidance varies with potential cost, then a decision-making process is evident and the behaviour is not a mere reflex.
Hermit crabs are naked crabs that occupy the discarded shells of other species. In the first experiment, Elwood and Appel (2009) wanted to know whether electric shocks would induce crabs to move out of their shells.
Hermit crabs were induced into shells of both good and poor quality. Some shells had wires attached to deliver small shocks to the crab's abdomen. However these shocks were just under the level that would normally induce a crab to move out. Both groups - shocked and non-shocked - were then offered new shells. The scientists wanted to see if a) the shocked crabs would be more likely to vacate their existing shell b) if the quality of the shell would be a factor in encouraging the crab to swap.
They found that the shocked crabs were more likely to move out of the 'shock' shell and into a new one. They also did this more quickly than the non-shocked crabs; and were significantly more likely to do this if the shell they were occupying was of poor quality. The crabs were 'trading off', suggesting that the experience of pain from just a small shock was sufficient for them to swap shell. The team also found that they retained a memory of the shock for 24 hours.
Professor Elwood stated "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". (5)
A second series of experiments in 2016 looked at a different kind of trade-off (7). Researchers in this study examined hermit crabs' responses to electric shocks within their shells when they were exposed to predator odours, non-predator odours or no odours at all. Results indicated that those exposed to predator odours were less likely to evacuate their shells compared with crabs exposed to no odours. The authors conclude that the crabs were trading off avoidance of electric shocks with predator avoidance. It was concluded that the crabs response is not simply reflex.
Grooming In Glass Prawns (6)
Elwood et al (2008) also conducted experiments with glass prawns, to study the effect of both pain and pain-relieving substances. An acidic substance can be administered to a limb of a creature. If the animal experiences pain, they will generally groom the affected area to try and relieve it. The experience can be confirmed by administering a pain-relieving agent and observing whether the grooming activity stops.
Elwood and his team applied a small amount of acid on the antennae of a group of glass prawns. A control group had only water applied. It was duly observed that prawns who had acid applied groomed the affected antenna more than the prawns with only water applied. Likewise prawns who had anaesthetic applied before the acid was brushed on did not groom as much as those who had had no anaesthetic.
The results of these studies were widely reported in the media. Yet the implications of these findings - that millions of crustaceans are experiencing suffering in a food industry which treats them as insensible - has not been acted upon; and their welfare remains unprotected in law.
1.EFSA (European Food Safety Authority) (2005) "Opinion on the “Aspects of the biology and welfare of animals used for experimental and other scientific purposes” The EFSA Journal, 292, 1-46
2. Elwood, R., and Magee, B., (2013) "Shock avoidance by discrimination learning in the shore crab (Carcinus maenas) is consistent with a key criterion for pain", Journal of Experimental Biology, vol 216: 353-358
3. Morelle, J., (2013) "Further evidence crabs and other crustaceans feel pain", http://www.bbc.co.uk/news/science-environment-21044077, webpage, accessed 12-3-16
4. Appel, M & Elwood, R (2009), 'Motivational trade-offs and potential pain experience in hermit crabs' Applied Animal Behaviour Science, vol 119, no. 1-2, pp. 120-124
5.BBC, (2009) "Crabs sense and remember pain" http://news.bbc.co.uk/1/hi/northern_ireland/7966807.stm, accessed 12-3-16
6. Barr, S., Dick, JTA., Laming, P., & Elwood, R., (2008) "Nociception or pain in a decapod crustacean?" Animal Behaviour, vol 75:745-751
7 Magee, B., & Elwood, R. W. (2016). Trade-offs between predator avoidance and electric shock avoidance in hermit crabs demonstrate a non-reflexive response to noxious stimuli consistent with prediction of pain. Behavioural Processes, 130, 31-35.