Infection by (Trematoda) decreases grazing by the keystone gastropod, .

Parasites are well-known to alter the behavior of their hosts, but there is still a paucity of knowledge about how parasites modify the behavior of many ecologically influential host species. I studied the keystone grazer, the salt marsh periwinkle to determine the influence of infection by the digenetic trematode, on its grazing behavior. Comparative laboratory grazing studies of wild-collected and experimentally infected snails revealed that decreased grazing on live by more than 80%. Because of the large ecological influence of in southern U.S. marshes, parasite modification of snail grazing may have ramifications for marsh ecosystem stability if parasite prevalence is sufficiently high.