A Rough Relationship: New Records of Reciprocal Predation Between Pitvipers and Opossums

Feeding interactions between Bothrops pitvipers and Didelphis opossums are often framed as a coevolutionary interaction centred on venom resistance, in which the opossums seem to be resistant to venom toxins and can therefore consume venomous snakes. We report two instances of adult female Bothrops jararacussu feeding on Didelphis aurita in the Atlantic Forest of southeastern Brazil. We propose that the outcome of these interactions depends not only on the biochemical balance between venom composition and prey resistance, but also on species size, venom volume and the prey's ability to detect a cryptic ambush predator. Field observations show that Didelphis rarely detects Bothrops in natural encounters, suggesting that sensory limitations may play a central role in mediating predation outcomes. Together, our findings challenge the prevailing arms race paradigm and highlight the importance of ecological context in shaping predator-prey dynamics.