Many crotaline snakes exhibit envenomated-prey preference in laboratory experiments. We examined the ability of copperheads (Agkistrodon contortrix) to distinguish between envenomated and nonenvenomated tobacco hornworm larvae (Manduca sexta). Snakes directed significantly more tongue flicks at envenomated hornworms than at nonenvenomated hornworms, and snakes consumed envenomated hornworms more frequently than nonenvenomated prey. These results support the hypothesis that envenomated tissue is an important stimulus to copperheads during strike-induced chemosensory searching. Copperheads preferred hornworms envenomated by conspecifics in the relative order: Louisiana > Texas > Kansas; this preference matches the relative order of preference and venom potency documented in a previous study of copperheads for envenomated mice. We conclude that the venom protein-prey tissue interaction responsible for the observed behaviour is similar in both invertebrate and rodent prey items.