Interaction between olfactory and visual cues affects flight initiation and distance by the hermit crab, Pagurus bernhardus

Using multiple cues from a predator may increase the accuracy of risk assessment by providing information about the identity of the predator. We test this hypothesis using the hermit crab, Pagurus bernhardus (L.), responding to stimuli from a predatory crab, Cancer pagurus. Physical objects provided mechanical and visual stimuli, a Perspex sheet was used to provide mechanical stimulus, and a predatory crab model or a non-predatory 'block' provided visual stimuli. Physical stimuli were presented alone or in combination with odour from a live C. pagurus. The distances at which P. bernhardus stopped feeding, initiated flight and the distance ran were measured to assess perceived risk. Pagurus bernhardus showed no significant response when visual cues were absent. In response to the approach of a visual stimulus hermit crabs ceased feeding. Flight initiation occurred sooner in response to the crab model compared to the block indicating the importance of the shape of a stimulus in flight initiation. The presence of odour increased the distance run from the crab model but not the block. This use of multiple sensory systems to accurately assess predation risk may be important in environments such as the intertidal where the physical environment can disrupt cues.