Invasive Cane Toads as prey for native arthropod predators in tropical Australia

The successful spread of invasive Cane Toads (Rhinella marina) across tropical Australia has been attributed to a lack of biotic resistance, based upon the inability of most anuran-eating vertebrate predators to tolerate the powerful chemical defenses of the toads. However, despite their high species richness, invertebrates have been much less studied than vertebrates as predators of Cane Toads. Our field and laboratory studies show that toads are killed and consumed by a phylogenetically diverse array of arthropod taxa. No arthropod predators consumed toad eggs in our laboratory experiments, but fishing spiders, water beetles, water scorpions, and dragonfly nymphs killed toad tadpoles, and ants and fishing spiders killed metamorph toads. Published accounts report predation on toads by crustaceans and hemipterans also. In our experiments, no predators showed any overt ill effects from consuming toad tissue. Dragonfly nymphs (Pantala flavescens) and fishing spiders (Dolomedes facetus) selectively took Cane Toad tadpoles at higher rates than some simultaneously offered native frog tadpoles. In combination with published data, our experiments suggest that the tadpoles and metamorphs of Cane Toads face high predation rates from the diverse and abundant invertebrate fauna of aquatic and riparian habitats in tropical Australia. The invasion of Cane Toads can potentially have positive effects on populations of many native animal species.