Crabs are smarter than you might think Harald Schmidt/Shutterstock

A species of crab can learn to navigate a maze and still remember it up to two weeks later. The discovery demonstrates that crustaceans, which include crabs, lobsters and shrimp, have the cognitive capacity for complex learning, even though they have much smaller brains than many other animals.

“Crustaceans have a brain roughly 10 times less than the size of a bee’s in terms of neuronal count,” says Edward Pope at Swansea University in the UK.

Pope and his colleagues trained 12 shore crabs (Carcinus maenas) to complete an underwater maze in an aquarium. The maze had a single correct path to the end, which required five changes of direction and included three dead ends. The researchers placed a single crushed mussel at the end of the maze as a tasty reward.


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The crabs attempted the maze once a week for four weeks. They didn’t manage to complete the maze without making a mistake until their third week of training, although they improved after each training session. Pope and his team then waited an additional two weeks before putting the crabs’ memories to the test.

This time, the team put the crabs in a maze without an edible reward. All 12 managed to complete the maze within 8 minutes. By contrast, a group of untrained crabs took an average of 39 minutes to complete the maze, with only seven out of 12 crabs reaching the end in under an hour.

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“It’s interesting that the crabs can learn the maze,” says Neil Burgess at University College London, though they seem to learn more slowly than rodents or other mammals, he says.

Pope says his team next wants to investigate how changing ocean conditions, such as ocean acidification and rising temperatures, might impact the crabs’ ability to learn.

Journal reference: Biology Letters, DOI: 10.1098/rsbl.2019.0407