Active escape of prey from predator vent via the digestive tract

Predation pressures can lead to the evolution of escape behavior in prey animals [1,2]. Most previous studies investigated how prey can escape from predators before contact [1,2], whereas recent studies have focused on the post-contact escape of prey [2]. Predators can damage prey by biting or chewing, and the predator's digestive system ultimately kills almost all prey after swallowing. However, several species can survive passage through a predator's gut and are ultimately excreted with feces [3-5]. Such escapes from the predator's vent (cloaca or anus) are considered passive [3-5]. Survival in the extreme pH and anaerobic conditions of the predator digestive tract depends on the speed of passage and activity of the prey. This lethal environment may impose selective pressures on the evolution of quick and active escape behavior in swallowed prey species. Here, I report active escape of the aquatic beetle Regimbartia attenuata (Coleoptera: Hydrophilidae) from the vents of five frog species via the digestive tract. Although adult beetles were easily eaten by frogs, 90% of swallowed beetles were excreted within 6 h (0.1-6.0 h) after being eaten and, surprisingly, were still alive. When beetle legs were experimentally fixed with wax, all of the treated beetles were killed in the frogs' digestive system and finally excreted >24 h (38.3-150.3 h) after consumption. Therefore, swallowed beetles likely used their legs to move through the digestive tract toward the frog vent, hastening their escape. This study is the first to document active prey escape from the vent of a predator and to show that prey may promote predator defecation to hasten escape from inside the predator's body.