Pond frog as a predator of hornet workers: High tolerance to venomous stings

Abstract

Some animals use stingers to repel attackers, and some predators have evolved tolerance to such stings, enabling them to consume venomous prey. For example, social wasps, such as hornets, use modified ovipositors as venomous stingers to inject venom, which can cause intense pain in humans. The world's largest hornet, Vespa mandarinia (Hymenoptera: Vespidae), stores huge amounts of venom in its abdomen, which can kill mammals. Although some animals are known to prey on adult hornets, it remains unclear whether these predators can avoid or tolerate their venomous stings. Adult hornets have been found in the stomach contents of some amphibian predators, including the pond frog Pelophylax nigromaculatus (Anura: Ranidae), suggesting that they can successfully attack and consume hornets. To examine whether frogs avoid or tolerate hornet stings, the pond frog P. nigromaculatus was experimentally presented with stinging females (workers) of three Japanese hornet (Vespa) species—V. simillima, V. analis, and V. mandarinia—under laboratory conditions. Almost all frogs attacked the hornets, and the hornets were observed stinging the frogs during these attacks. However, 93%, 87%, and 79% of the frogs ultimately consumed V. simillima, V. analis, and V. mandarinia, respectively. Hornet stings neither killed nor harmed the frogs. These results suggest a high tolerance of pond frogs to the venomous and painful stings of giant hornets. Frogs may serve as useful model organisms for investigating the physiological mechanisms underlying the intense pain and lethal effects of hornet stings in vertebrates.