Contemplating the crustacean IQ

Crabs, lobsters, shrimp and other crustaceans are more developed than once thought

Barbara Julian

Barbara Julian

When we say something crawled out from under a rock we usually mean something ugly and moronic. When we explore tidepools what usually scuttles out from under rocks are crabs, but although they may look ugly, science has established that they are not moronic.

The ones we see on local beaches are the hermit crabs, the green and purple shore crabs, and the long-legged kelp or spider crabs. Beyond low tide live the larger orange-coloured Dungeness crabs. These are the ones being harvested in traps marked by floats often seen off the Oak Bay Marina and the Yacht Club. (The crabs must have reached a certain diameter before harvesting however, for it takes them two years to reach maturity during which they transform in stages from legless larvae into adults with those familiar large serrated claws.)

Whenever I surprise a group of crabs by turning over their rock in a tide pool, I’m struck by how quick and determined they are in escaping. Zoologist John Baker of the University of Oxford tells us that this is because their sensory organs are highly developed, their nervous systems complex and very similar to our own, and their responses to stimuli immediate and vigorous. He believes, therefore, that they feel pain and that dropping them into boiling water can cause agony for as long as two minutes.

Even people who no longer eat fellow-mammals often assume that crustaceans such as crabs, lobsters, shrimp and prawns are too simple to suffer. Apparently they’re wrong about that. Like mammals, the crusty creatures produce opioids, molecules which counter the transmission of pain through nerve cells. Opioids act like opium, making them “nature’s painkillers,” and they could only evolve in species that feel pain.

Animal behaviourist Dr. Donald Griffin learned that crabs remember painful and threatening objects or situations when he devised studies showing that they learn to avoid these. They show understanding and memory both of places and of other individuals, and form social hierarchies when a number of them are kept confined together.

After reading that, I can’t pass a crab tank in a grocery store without averting my eyes. The lucky un-caught crustaceans under the sea have their own problems however. Crabs eat live prey such as clams, snails, worms, fish and seaweeds, but they also scavenge detritus from the ocean floor. Between their shell-moults, when a new shell is still soft, and when females are carrying eggs on their abdomen, they shelter by burrowing in mud and there they encounter pollutants in run-off from storm drains and industrial sites.

Sediment from shoreline logging and construction can prevent them from feeding and breathing. The intake of heavy metals and pesticides must be hard not only on them but also on the bodies of the halibut, herons, otters and humans that eat them. Crabs do what they can to avoid these troubles and as science has discovered, they can do more than we had assumed possible for such an archaic-looking life form.

Contemplating this news about crustacean IQ, I decided to do a little citizen-science.

I thought the crab’s cousin the crayfish would be a fit subject to gently test and observe for responses, and that one of its habitats – Bowker Creek – would make a handy living laboratory. I had been told by the “green men” (a.k.a. homeless campers in the area who know the creek well), that Bowker harbours crayfish. Yet no matter how often I look, I have yet to spot one there.

Maybe that in itself tells us something: the smartest thing a creature can do in this dangerous world of polluters and predators, is to stay out of sight.




Barbara Julian is a local writer and nature enthusiast who writes monthly  on Oak Bay’s suburban wildlife.