Larval period in Lithobates catesbeianus is set largely by temperature and food rather than by a fixed schedule. In the southern parts of the native range, tadpoles hatched in spring can metamorphose the same year. Further north, and at higher elevation, the larva overwinters as a tadpole, and two or three years to metamorphosis is normal.
A long larval period produces a very large tadpole, sometimes exceeding fifteen centimetres including the tail, which is bigger than many adult frogs of other species. Adults reach around twenty centimetres in body length and take an additional two to three years to reach breeding condition.
The same flexibility helps make the bullfrog invasive. Where it has been introduced, in the western United States, parts of Europe, Japan and South America, it eats a wide range of native vertebrates including other frogs, and it can carry the amphibian chytrid fungus Batrachochytrium dendrobatidis while showing relatively low mortality from it, making introduced populations a possible reservoir for the pathogen.