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Larvae of the mayfly Siphlonisca are predators of the detritivorous mayfly Siphlonurus in floodplain wetlands in Maine (USA). Both mayflies are natural prey of brook trout (Salvelinus fontinalis). We exposed larvae of Siphlonurus and Siphlonisca to chemicals from injured conspecifics and their predators. Significant decreases in movement activity by Siphlonurus were elicited by chemicals released from Siphlonisca, chemicals released from brook trout fed conspecifics, and by chemicals released from injured conspecifics. A significant decrease in movement activity by Siphlonisca was elicited by chemicals released from brook trout fed either conspecifics or Siphlonurus. Movement activity by either Siphlonurus or Siphlonisca was not significantly affected by chemicals released from trout feeding on brine shrimp (Artemia). Both Siphlonurus and Siphlonisca were able to detect chemicals that provided information about past feeding behaviour by brook trout. However, their response to the chemicals used in this study was context-specific. A reduction in movement activity, a behavior that presumably reduces the probability of being consumed by visual predators, occurred only when mayflies were exposed to chemicals released by brook trout feeding on conspecific (Siphlonurus) or confamilial (Siphlonisca) prey.