The scent of cannibalism: The olfactory basis of cannibalism in hermit crabs

Animals are constantly exposed to sensory cues that provide conflicting information about their environments and must somehow rely on these sensory cues to make appropriate behavioral decisions. For cannibalistic scavengers, the odors of injured conspecifics or heterospecifics can serve as conflicting sensory cues because they could represent either the proximity of a food resource or the proximity of a predator (e.g., a recent predation event). Foraging cannibals must therefore weigh the risk-reward consequences of approaching injured conspecifics and heterospecifics. Previous research has shown that foraging cannibals respond to these conflicting cues by exhibiting caution, showing anti-predation behaviors instead of foraging behaviors. Hermit crabs are cannibalistic animals that rely heavily on olfaction to forage. Here I show for the first time that cannibalistic hermit crabs use the odors of crushed conspecifics and heterospecifics as foraging cues instead of anti-predation cues. Test animals, in general, responded to the odors of crushed conspecifics and heterospecifics with increased foraging responses instead of anti-predation responses, and readily consumed both conspecific and heterospecific animals. However, test animals showed faster approach times and longer feeding times for heterospecifics than conspecifics. These results suggest that hermit crabs are capable of discerning between the odors of conspecifics and heterospecifics, and show greater avoidance towards dead conspecifics than heterospecifics.