Frogs are carnivorous amphibians, and for many people, their diet is synonymous with insects. While most adult frogs rely on insects, their menu is surprisingly diverse. A frog’s diet is dictated less by the prey’s classification and more by two simple factors: movement and size. If a potential meal moves and fits into the frog’s mouth, it is likely on the menu, allowing them to consume a vast array of non-insect life forms.
The Invertebrate Menu Beyond Insects
Arachnids, which include spiders and mites, are a common food source captured by the frog’s sticky, projectile tongue as they encounter them in their terrestrial habitats. These creatures provide a protein-rich meal that is easily digested by most species.
Annelids, such as earthworms and nightcrawlers, are frequently consumed, especially by species that forage on damp ground or near water. These soft-bodied worms are easy for a frog to swallow whole. Aquatic and semi-aquatic frogs may also feed on crustaceans, including small shrimp, amphipods, or juvenile crayfish.
Mollusks, like slugs and small snails, are also preyed upon by many frog species. The shells of smaller snails can sometimes be crushed by the stronger jaws of certain frogs, allowing access to the soft tissues inside.
Vertebrates: When Frogs Hunt Bigger Prey
The largest species of frogs possess the bulk and jaw strength to consume vertebrate animals. Species like the American Bullfrog or the African Bullfrog routinely expand their diet to include animals much more substantial than typical invertebrates. This predatory behavior is possible because of their immense size and ability to swallow prey whole.
Larger aquatic frogs frequently prey on small fish, using their powerful hind legs to lunge and engulf them underwater. On land, these formidable hunters may consume small reptiles, such as lizards or juvenile snakes, and even small birds that they manage to ambush.
Intraspecies predation is also common, with large frogs cannibalizing smaller frogs, tadpoles, or salamanders. To manage such large prey, some species, like the African Bullfrog, have bony, tooth-like projections called odontoid processes on their lower jaw that help them hold onto struggling prey. Frogs also use their eyeballs, which retract slightly into the skull, to help physically push large food items down the throat during swallowing.
Tadpole Diets and Specialized Feeding
The larval stage is a significant departure from the adult frog’s carnivorous diet, as tadpoles consume a largely non-animal diet. Most tadpoles are herbivorous or omnivorous, feeding primarily on algae, decaying organic matter, and detritus. Their digestive systems are adapted for this, featuring a long, coiled gut necessary to break down plant material efficiently.
As they grow, some tadpoles become omnivores, scavenging on dead insects or other organic debris. In specialized cases, such as the Mexican spadefoot toad tadpoles, some individuals may develop broader heads and shorter guts, becoming carnivorous and even cannibalizing smaller siblings.
Beyond the tadpole stage, a few rare adult species have specialized feeding habits that do not involve animal prey. For example, the Brazilian tree frog, Xenohyla truncata, consumes fruit and nectar. This unique behavior makes the frog a seed disperser, demonstrating that exceptions exist where adult frogs incorporate plant matter into their diet.