Shake it off: behavior of a freshwater snail during and after parasite exposure

Snails serve as important intermediate hosts for a number of ecologically important trematode species. Despite this, few studies have considered how snails behave in the presence of parasites. Here, we use a common genus of host snail, Physa Draparnaud, 1801, and echinostome parasites to explore how snails respond to parasite exposure. To examine this relationship, we exposed 26 Physa snails to echinostome cercariae, a larval parasite that actively pursues and encysts within snails. The behavior of exposed snails was recorded and compared to the behavior of unexposed snails ( N = 26). Snails exposed to parasite cercariae displayed significantly more shell shaking, more surfacing, and less time foraging than unexposed snails. Snails were additionally monitored for behavioral changes several days after infection; however, no behavioral impacts persisted beyond the initial exposure period. These results suggest that shell shaking, commonly assumed to be an antipredator response, may be a general response to mechanical stimulation including parasite exposure. The combination of these behaviors is likely to have ecological ramifications including altered interactions with predators and changes in snail foraging.