IntroductionPredation is a complex process for which behavior, morphology, and size of both predator and prey can affect the success and effectiveness of the predator. For predators such as snakes that swallow prey whole, gape ultimately limits prey size, but the behaviors used to select, capture, and consume prey and attributes of the prey can also affect maximal prey size. For example, swallowing live, struggling prey is difficult, but using coiling or envenomation to restrain or kill prey has evolved repeatedly in snakes.MethodsTo test the potential benefits of these behaviors, we manipulated the type and size of prey, and determined how stereotyped predatory behavior was in a snake species (Liodytes rigida) that uses both coiling and envenomation to restrain and immobilize its formidable prey of crayfish. We also studied a close relative (Liodytes pygaea) that eats fish and salamanders to gain insights into the evolution of these traits.ResultsForL. rigida, envenomation of hard-shell crayfish via their soft underside was very stereotyped (100% of feedings). Envenomation of soft-shell crayfish was less frequent (59% of feedings) but became more likely both with increased relative prey size and increased time after molt (hardness).L. rigidacoiled more for hard-shell than soft-shell crayfish (77% vs. 30%). The probability of coiling was unaffected by prey size, but it increased with increased time after molt for the soft-shell crayfish.Liodytes rigidawaited to swallow crayfish until they were completely immobile in 75% and 37% of the feedings with hard- and soft-shelled crayfish, respectively. Even with large preyL. pygaeanever used coiling or envenomation, whereas previous studies ofL. alleni, the sister species ofL. rigida, observed non-lethal coiling without envenomation when eating hard-shell crayfish.DiscussionOur findings for theLiodytesclade of three species suggest that coiling evolved ancestral to the crayfish specialists (L. alleni;L. rigida), and envenomation byL. rigidasubsequently evolved as an additional means of subduing formidable prey. The proximate benefits observed for coiling and envenomation inL. rigidasupport the evolutionary scenario that both traits evolved to enhance the feeding performance for more formidable prey.