Cutaneous respiration
The skin of amphibians is a major site of respiration in all species for which measurements are available. Cutaneous respiration is the sole respiratory mode of lungless salamanders (family Plethodontidae) which lack lungs entirely yet constitute the largest family of salamanders. Cutaneous respiration in frogs and other amphibians may be the primary respiratory mode during colder temperatures.
Lithobates heckscheri
Adult river frogs have a home range of about . They are largely nocturnal and feed on insects and other invertebrates, as well as small vertebrates, including frogs. They spend much of their time in water and are relatively bold. During hot weather they are normally found sitting in moist or wet places, presumably to avoid desiccation. When the temperature falls below about they are no longer to be seen in their normal habitat and are likely to be seeking refuge from the cold under water.
Breeding takes place between April and August with males calling from the edge of ponds and swamps from April to July. The call has been described as "a deep, low-pitched, rolling snore". The eggs are laid in a floating layer among emergent vegetation, a clutch numbering several thousand eggs which hatch after about three days. The tadpoles are at first a dark color but become much paler over time with a dark edge to the tail fin. They congregate in the shallows in the daytime, sometimes in dense swarms, but move into deep water at night. They feed on both animal and vegetable matter. They remain as tadpoles for a long period, overwintering once or twice, and reaching a snout-to-vent length of or more. After metamorphosis, the newly emerged juveniles are long and move away from the margins of the water. The large number of juveniles compared to the relatively small number of adults indicates a high mortality rate for newly emerged young. Predators that feed on tadpoles and juveniles are thought to include the banded water snake ("Nerodia fasciata"), other water snakes ("Nerodia" sp.), the largemouth bass ("Micropterus salmoides") and the grackle ("Quiscalus" sp.). However the skin may contain some noxious substances or malodorous secretions as some snakes, including the indigo snake ("Drymarchon"), have been observed gagging and retching after eating a river frog. Even after the frog has been regurgitated, the snake continued to wipe its mouth on the ground.