This frog is native to southern and eastern parts of the United States and Canada, but has been widely introduced across other parts of North, Central and South America, Western Europe, and parts of Asia, and in some areas is regarded as an invasive species. The male bullfrog defends a territory during the breeding season. His call is reminiscent of the roar of a bull, which gives the frog its common name. Bullfrogs are sexually dimorphic, with males being smaller than females and having yellow throats. Males have tympani larger than their eyes, whereas the tympani in females are about the same size as the eyes.