American Bullfrog (Lithobates catesbeianus)
Order Anura, Family Ranidae (True Frogs), Genus Lithobates, Species catesbeianus. Ranids are characterized by smooth, moist skin, large tympana, and powerful hind legs for jumping.
Species
American Bullfrog (Lithobates catesbeianus)
Family
Order Anura, Family Ranidae (True Frogs), Genus Lithobates, Species catesbeianus. Ranids are characterized by smooth, moist skin, large tympana, and powerful hind legs for jumping.
Size
The largest frog in North America. SVL ranges from 9 to 15 cm (3.5 to 6 in), but can reach 20 cm (8 in). They can weigh over 0.5 kg (1.1 lbs). Tadpoles are also exceptionally large, reaching up to 15 cm before metamorphosis.
Conservation
IUCN Status: Least Concern. Populations are stable and expanding internationally. In many areas outside their range, they are a threat to local biodiversity and are subject to eradication efforts.
Description
The American Bullfrog is the quintessential 'pond frog.' Iconic for its size and booming voice, it stands as a dominant predator in freshwater ecosystems. Its stoic posture and vibrant green face make it a favorite for nature photographers.
Key Features
Large size (over 4 inches), green to brown coloring, massive tympanum, and specifically the lack of skin ridges (dorsolateral folds) running down the back.
Physical Description
A very large, robust frog with a wide, blunt head and large gold-to-hazel eyes. It features a prominent tympanum (eardrum) located just behind the eye. It lacks dorsolateral folds (ridges) along its back, which is a key trait of this species.
Skin Texture & Coloration
The skin is relatively smooth but can be granular or tuberculate on the back. Coloration is typically olive green to brownish-green, often with dusky spots or mottling. The underside is white or cream, sometimes with yellow on the throat of males.
Distinguishing Features
The most critical marker is the lack of dorsolateral folds; instead, a ridge runs from the eye, around the tympanum, and down toward the shoulder. In males, the tympanum is significantly larger than the eye, whereas in females, it is roughly the same size.
Habitat
Highly aquatic; found in permanent bodies of water such as lakes, ponds, marshes, and sluggish rivers. They prefer warm, shallow water with abundant vegetation for cover and hunting.
Geographic Range
Native to central and eastern North America. However, it has been widely introduced to the western United States, Europe, South America, and Asia, where it is often considered an invasive species.
Behavior
Primarily nocturnal but active during the day. They are solitary and highly territorial. They are sit-and-wait predators. When startled, they often leap into the water with a loud 'yelp' or 'eEP' sound.
Diet & Feeding
Gape-limited generalists; they will eat anything they can swallow, including insects, crayfish, fish, turtles, snakes, birds, bats, and other frogs (including their own species).
Reproduction
Breeds in late spring and summer. Males congregate in choruses to attract females. Females lay up to 20,000 eggs in large floating masses. Amplexus is axillary (behind the front legs).
Vocalizations
A deep, resonant, bass-like 'jug-o-rum' or 'br-wum'. It is a low-frequency hum that can carry over long distances across water.
Life Cycle
Eggs hatch in 3–5 days. The tadpole stage is unusually long, lasting 1 to 3 years depending on the climate. Adults can live 7–10 years in the wild and up to 15 years in captivity.
Conservation Status
IUCN Status: Least Concern. Populations are stable and expanding internationally. In many areas outside their range, they are a threat to local biodiversity and are subject to eradication efforts.
Toxicity & Defense
Not toxic to humans. They rely on camouflage, their massive size to intimidate or overpower predators, and powerful legs to escape. They may secrete a mild mucus that is unpalatable to some predators.
Ecological Role
A top-tier predator within its niche, controlling insect and small vertebrate populations. However, as an invasive species, they can decimate local amphibian populations through predation and competition.
Similar Species
Green Frog (Lithobates clamitans), which is smaller and possesses distinct dorsolateral folds that extend halfway or more down the back. Pig Frog (Lithobates grylio), which has more pointed toes and a different call.
Observation Tips
Best found on warm summer nights along the edges of permanent ponds using a flashlight. Their eyes reflect a bright gold-white shine (eyeshine) in the beam of a light.
Handling & Safety
Safe for humans but should be handled with wet hands to protect their skin. Large adults have a strong grip and can potentially bite, though it is rare. Always wash hands after contact to prevent salmonella transmission.
Seasonal Activity
Active from spring through early autumn. They hibernate (brumate) underwater, buried in the mud or resting on the bottom of ponds that do not freeze solid.
Cultural Significance
Famous in literature (Mark Twain's 'The Celebrated Jumping Frog of Calaveras County') and as a source of frog legs in culinary traditions globally.
Interesting Facts
Bullfrogs are famous for their ability to jump up to 10 times their body length. They are also 'gap-limited' predators, meaning they are only limited in diet by the size of their mouth, leading to records of them eating small birds and bats.