The American bullfrog (Lithobates catesbeianus) is a prominent amphibian, recognized as the largest true frog species in North America. This semi-aquatic creature is well-known for its deep, resonant call, which often sounds like a “jug-o-rum” or “br-wum,” echoing across its watery habitats. Its substantial size and adaptable nature allow it to thrive in diverse freshwater environments, making it a familiar presence across many regions.
Key Characteristics
Bullfrogs possess distinctive physical attributes that aid in their identification. They are notably large, typically measuring between 9 to 20 centimeters (3.6 to 8 inches) from snout to vent, with some individuals reaching up to 500 grams (1.1 pounds) or more. Their coloration varies from shades of olive-green and brown, sometimes featuring mottling or banding of grayish-brown, while their underside is generally off-white with yellow or gray blotches. The skin of a bullfrog is smooth, lacking the dorsolateral folds (ridges of skin) found along the backs of many other frog species; instead, a raised ridge curves from behind the eye and around the eardrum, or tympanum.
In male bullfrogs, the tympanum is noticeably larger than their eye, whereas in females, it is approximately the same size or smaller. Their front toes are not webbed, but the hind feet are fully webbed, except for the last joint of the longest toe, which aids in powerful swimming. Males are known for their distinctive, loud call, which can travel up to a quarter-mile, and during breeding season, their throat may also turn yellow.
Natural Habitat
American bullfrogs are highly aquatic and primarily inhabit permanent freshwater bodies. These include ponds, lakes, slow-moving streams, marshes, swamps, and even human-made environments like ditches, canals, and reservoirs. Their reliance on consistent water sources is particularly important for breeding and providing shelter. Bullfrogs prefer warm, still, and shallow waters, often with dense vegetation, which offers both cover and hunting grounds.
Native to eastern North America, their natural range extends from the eastern Canadian Maritime Provinces south through the eastern United States to Florida and west to Texas. However, they have been widely introduced across the western United States, including states like California, Oregon, and Washington, and in various other parts of the world, such as South America, Asia, and Europe. In these introduced regions, they are sometimes considered an invasive species due to their adaptability and impact on local ecosystems.
Diet and Behavior
Bullfrogs are voracious, opportunistic ambush predators with a broad diet. Their carnivorous diet includes a wide array of prey, from insects and crustaceans to small fish, other frogs, and even small birds or rodents. They typically wait for prey to come within striking distance, then launch themselves forward with their powerful hind legs. Once close, they use a sticky, muscular tongue to capture their prey, which is attached at the front of the mouth allowing for maximum reach.
Bullfrogs possess tiny teeth on the roof of their mouth that help prevent prey from escaping once caught. To swallow large meals, they use their eyeballs to help push the food down their esophagus. Adult bullfrogs are generally solitary, and males establish and aggressively defend territories during the breeding season through calls, physical displays, chases, and even wrestling with rival males.
Life Cycle
The life cycle of a bullfrog involves several distinct stages, beginning with eggs laid in water. Females can lay a substantial number of eggs, typically ranging from 6,000 to 20,000 in a single mass, which forms a floating film on the water’s surface. These eggs usually hatch within two to five days, depending on water temperature.
Upon hatching, the bullfrog enters the tadpole stage, characterized by gills for underwater respiration and a tail for swimming. Bullfrog tadpoles are primarily herbivorous, feeding on algae and other small particles. This larval stage is notably long compared to many other frog species, lasting anywhere from one to three years, especially in colder climates where development slows. During this period, they gradually undergo metamorphosis, developing limbs, reabsorbing their tail, and transforming their gills into lungs, preparing them for a more terrestrial adult life. After metamorphosis, they become froglets, which then mature into adult bullfrogs. Adults typically reach sexual maturity between two to five years of age. In the wild, bullfrogs generally live for 7 to 10 years, though some individuals in captivity have been known to live for nearly 16 years.