The American bullfrog (Lithobates catesbeianus), commonly known as the bullfrog in Canada and the U.S., is a large true frog native to eastern North America. It typically inhabits permanent water bodies like swamps, ponds, and lakes, as well as manmade habitats such as pools and canals. Named for the bellowing sound made by males during breeding season, bullfrogs are widely eaten, especially in the southern U.S. Their popularity as a food source has led to their introduction worldwide, where they are often considered an invasive species due to their high reproductive rates and voracious appetite, negatively impacting native wildlife. Aside from being a food source, bullfrogs are used for dissection in science classes, and albino bullfrogs are sometimes kept as pets.
The dorsal surface of the bullfrog is olive-green and may have mottling of grayish-brown, while the ventral surface is off-white with yellow or gray blotches. The bullfrog has small teeth for grasping, prominent eyes with brown irises, and noticeable tympana behind the eyes. Its limbs are banded with gray, with short forelegs and long hind legs; the back toes are webbed except for the fourth toe.
Bullfrogs are sexually dimorphic, with males smaller and having yellow throats and larger tympana than their eyes, while females have tympana about the same size as their eyes. They grow quickly in their first eight months and can reach weights up to 500 g, with some individuals even reaching 800 g. They are the largest true frog species in North America.
Originally native to eastern North America, bullfrogs have been introduced across many U.S. states, Hawaii, and various other countries. In some regions, they are considered invasive, threatening local reptiles and amphibians by outcompeting or preying on them, and potentially spreading chytridiomycosis, a lethal fungal infection affecting native frogs.
The bullfrog breeding season lasts about two to three months, typically beginning in late May or early June and extending into July. Territorial males call loudly from spaced areas to establish their presence, using different types of calls: territorial, advertisement, and encounter calls. Males are present in breeding ponds longer than females, increasing their chances of mating, while females have shorter periods of receptivity, usually lasting only one night.
Males clasp receptive females using forelimbs, a trait that has shown sexual dimorphism, with males having significantly stronger muscles. This allows them to maintain amplexus longer, enhancing reproductive success in a competitive environment. Consequently, male-to-male competition is high, and female choice in mating is intense. Kentwood Wells categorized bullfrog mating systems into leks and resource-defense polygyny, highlighting males’ territorial defense and attractor behavior.
