Safe or in danger? Time and distance of reaction in hermit crabs to a risk of predation

ABSTRACT Escape decisions to predators are influenced by aspects such as prey’s visual perspective, in which visual cues are essential to detect and react to predators. Crabs use the visual sense to detect and scaling potential threats. Here, we evaluate the escaping response of free-ranging Pacific hermit crab (Coenobita compressus) after showing them stimuli differing in size and shapes that resemble potential threats. We conducted a field experiment on 150 individuals of Pacific hermit crab. The crab’s reaction time and distance was recorded with respect to five predator models (large bird, small bird, large square, small square, and null model), additionally, the shell size of each crab was measured. We found that crab reaction time and distance are influenced by the large bird and large square models while shell size had no effect. Our results suggest that Pacific hermit crabs in this population have the ability to discriminate predators and base their escape response depending on the size and shape of the predator.