Effects of Predator Species and Size on Prey Escape Success Through the Digestive Tract

Many animals flee from their predators before capture. However, some species can successfully escape even after being swallowed. The likelihood of postcapture escape may be influenced by predator species and size, although this hypothesis has rarely been tested. In this study, I systematically investigated the escape success of the aquatic beetle Regimbartia attenuata (Coleoptera: Hydrophilidae) after being swallowed by six predator species-five native frog species (Anura: Ranidae, Dicroglossidae, Hylidae) and one non-native bullfrog, Aquarana catesbeiana (Ranidae)-which differed in body size, taxonomic affiliation, and their evolutionary history of coexistence with the beetle. Among adult R. attenuata individuals that were ingested, 79% survived passage through frog digestive tracts and successfully escaped from the vent (cloaca). Escape rates ranged from 57% to 91% across frog species. However, escape success was not significantly influenced by beetle size, frog species, or frog size. All surviving beetles escaped within 7 h after ingestion, whereas beetles that died inside the frogs were excreted much later, between 19 and 161 h postingestion. The time required for live beetles to escape through frog digestive tracts was significantly different from the time required for dead beetles to be excreted. Therefore, the active movement of adult R. attenuata through the frog digestive tract towards the frog's vent likely facilitated their successful escape through the cloacal aperture across various frog species and body sizes-including the non-native A. catesbeiana-with consistently high frequency.