A paper published recently in PLoS ONE shows that yabbies can not only recognise the faces of sparring partners but remember them for a day or more. (Memory is better in the vanquished than the vanquisher.)
How do they tell each other apart? Face width seems to be important. The little crusties can tell a fat head from a narrow one. Other characteristics play a role but zoologists at the University of Melbourne suggest that it's the combination rather than a specific feature that helps in yabby-to-yabby identification.
- The face of C. destructor. (a) Features analyzed on a yabby's face. Colour hue and saturation taken from the mean of 5 points. (2 marked by white triangles.) (b) PCA factor analysis of facial features.
You can read the paper (including details of how the researchers
Van der Velden, J, Zheng, Y, Patullo, BW & Macmillan, DL. (2008). Crayfish recognised the faces of fight opponents. PLoS ONE 3(2): e1695. Published online 2008 February 27. doi: 10.1371/journal.pone.0001695.