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Crayfish never forget the face of a foe

Image: Fighting yabbies (Cherax destructor)
In the study, scientists arranged fights between Australian crayfish, also known as Cherax destructor. Losers later preferred sparring with known rivals.David Paul / Blair Patullo / The University of Melbourne
/ Source: LiveScience

You looking at me, crayfish face?

It seems that crayfish don't forget a face — at least, not those of their foes.

Australian crayfish, also known as Cherax destructor, usually fight when they meet. After observing some such clashes, researchers isolated losers and gave them a choice between their former opponents — the faces of which scientists dabbed with yellow dye — and unpainted crayfish they had not fought before.

The researchers found the losers preferred the opponents they knew rather than the rival they did not, revealing the crustaceans recognized faces. "This suggests they are looking at each other more than we thought," said researcher Blair Patullo, a zoologist at the University of Melbourne in Australia.

The crayfish also recognized other crayfish even when there was no paint. They could even see past simple attempts to fool them — for instance, if a crayfish fought an opponent with a narrow face, he did not confuse another foe with a narrow face with its old enemy.

"Because we were unable to trick them, it suggests that their visual systems, or how we test for recognition, is more complicated than we had time to investigate," Patullo told LiveScience.

Understanding how crayfish recognize faces could help in developing feature recognition in robots, said researcher David Macmillan, head of zoology at the University of Melbourne.

The scientists did manage to fool the crayfish when they used identical twins. Still, no disappointment there — "even we as humans struggle to distinguish between twins based on vision alone," Patullo noted.

The scientists detailed their findings Feb. 28 in the journal PLoS ONE.