Crabs: A Landmark Study

Natural History, April, 2001 by Richard Milner

Some crabs find their way back home the same way people do--by observing and memorizing landmarks. Biologist Stefano Cannicci, of the Department of Animal Biology and Genetics at the Universita degli Studi di Firenze, and colleagues studied the homing behavior of Thalamita crenata, a crab found in large numbers on an intertidal mudflat north of Mombasa, Kenya.

In one set of trials, the researchers left variously colored concrete bricks and tiles around the animals' underwater dens for a few days, until they became accustomed to the objects. The artificial landmarks were then repositioned in the same configuration some distance away, and the crabs were displaced from their dens. Continuing to use the old landmarks, the crustaceans aimed for a "false home," directed by the misleading information they were given. The researchers concluded that the crabs showed good spatial knowledge and cognitive memory, resulting in a much more flexible orienting mechanism than those of other crabs--"comparable to the route-based memory of honeybees." ("Homing in the Swimming Crab Thalamita crenata: A Mechanism Based on Underwater Landmark Memory," Animal Behavior 60, 2000)