Frogs: The Animal Answer Guide

7. Food and Feeding

76 What do frogs eat? With few exceptions, all adult frogs and toads eat other animals—that is, they are carnivores. Frogs are well known for their insect-eating capabilities , and, in general, insects play a major role in their diet. However, frogs will eat any animal small enough for them to swallow, and because most frogs are small animals, insects and other small invertebrates, which are abundant in most ecosystems, form the bulk of their diet. In contrast to adult frogs, most tadpoles are herbivores, eating algae they scrape off of rocks and aquatic vegetation. Some tadpoles also feed on the detritus that accumulates at the bottom of the aquatic habitats in which they live. Although most frogs are generalists, some frogs specialize on particular types of prey. The Mexican burrowing toad (Rhinophrynus dorsalis) is a dumpy, short-legged frog adapted for burrowing underground. It rarely surfaces, except to breed, and feeds exclusively on ants and termites. The snout of the Mexican burrowing toad is pointed, and its small specialized mouth can engulf large numbers of tiny insects. The crab-eating frog (Fejervarya cancrivora) of Southeast Asia eats mostly small crabs in its mangrove habitat. Some large frogs have mouths big enough to eat other animals approximately their own size. The horned frogs of South America (genus Ceratrophrys ) are sit-and-wait predators capable of eating small rodents, small birds, and other frogs. The African bullfrog (Pyxicephalus adspersus) is similar to the horned frogs of South America but grows much larger and can eat even larger prey. Because the North American bullfrog (Rana catesbeiana ) is large, it can eat nearly any frog with which it shares its habitat. Chapter 7 Food and Feeding 77 Food and Feeding The bullfrog has been introduced by humans into many areas of the world where it is not native, which has posed a problem for native frogs that have not evolved to share a habitat with another frog that can eat even the largest adults of their species. As a rule, strict carnivores do not eat plants, but frogs may accidentally ingest plant material while struggling to swallow their prey. There are, however, a few frogs, that as adults develop the ability to incorporate significant amounts of plant material into their diet. The Indian five- fingered frog (Euphlyctis hexadactylus) is found in India and Bangladesh, and as it grows, the adult switches from eating insects to a diet of nearly 80 percent leaves and 20 percent mostly invertebrates. The Brazilian treefrog (Xenohyla truncata) is the only species of frog known to specialize on fruit. Research conducted by Hélio R. da Silva and his colleagues near Rio de Janeiro, Brazil, showed that this species consumed a variety of fruits, which formed an essential component of their diet. This treefrog did not specialize on any particular type of fruit but basically ate fruit according to its availability. Research on the diet of anurans can provide important information for their conservation. Ann Anderson and her colleagues conducted research on three species of sympatric toads found in the High Plains of Texas and New Mexico. These toads all breed in playa wetlands, temporary lakes that form during spring or summer rains. Researchers found that all three toads depend on species of invertebrates, especially beetles, found in the grasslands surrounding the wetlands, thus emphasizing the need to conserve not only the wetland habitats where these species breed but also significant critical habitat surrounding the wetlands. American bullfrogs (Rana catesbeiana ) will eat almost any kind of animal they can overpower and get in their mouth, including large crayfish. Courtesy Cris Hagen 78 Frogs: The Animal Answer Guide Do frogs chew their food? Frogs primarily eat their prey whole. Frogs may chew their prey to a small degree when positioning it in their mouths for swallowing, but mostly, prey is swallowed whole and often alive. Most frogs have teeth in their upper jaw, called maxillary teeth that help them to grasp and to hold onto prey. Many frogs will use their forelimbs to force prey into their mouths and their tongues to help push food backward and down their throat. Frogs will depress their eyes into their sockets when swallowing, and it has long been thought that this pressure may further help food to move into a frog’s esophagus. This contention had never been confirmed until Robert Levine of the University of...