Gherardi, F. and J. Tiedemann. 2004. Chemical cues and binary individual recognition in the hermit crab Pagurus longicarpus. Journal of Zoology, London 263:23-29.

Is individual recognition in the hermit crab Pagurus longicarpus based on chemical cues, visual cues, or both? Knowing that hermit crabs can distinguish a familiar crab from an unfamiliar crab, the next step in understanding how crabs make sense of their social environments is to narrow down the sensory mechanism involved.

A pheromone is a chemical released into the environment by an animal, which communicates something to a species member. Is it possible that hermit crabs communicate their identities with pheromones?

Crabs were paired up to attain familiarity, and then were placed individually in containers, each with an empty shell and in water with the scent of the familiar or an unfamiliar crab, and with the other crab either in sight, or not. Behavioural responses to the empty shell were noted. The results were that crabs reacted differently when they could smell familiar and unfamiliar crabs, and especially when they could smell and see them, but not when they could only see them. When there was no other crab scent, crabs reacted differently than when they could smell another crab.

This shows that crabs recognize one another by smell, and that they cannot recognize each other visually, but that sight and smell of another crab creates stronger recognition than smell alone. Also, a crab does not smell familiarity in another crab by merely recognizing its own scent on that crab, because crabs reacted differently in the presence of their own scents than in the presence of familiar crab scents.

(250 words)

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(posted May. 1 2005)