American Bullfrog (Lithobates catesbeianus)
Order Anura, Family Ranidae, Genus Lithobates, Species L. catesbeianus. True frogs (Ranidae) are characterized by powerful hind legs, smooth skin, distinct dorsolateral folds in many species, and highly aquatic habits.
Species
American Bullfrog (Lithobates catesbeianus)
Family
Order Anura, Family Ranidae, Genus Lithobates, Species L. catesbeianus. True frogs (Ranidae) are characterized by powerful hind legs, smooth skin, distinct dorsolateral folds in many species, and highly aquatic habits.
Size
Snout-to-vent length (SVL) ranges from 90 to 200 mm (3.5 to 8 inches), occasionally larger. Females are generally slightly larger than males. Weight can range from 300 to over 500 grams. Size at metamorphosis is quite large, often 35 to 60 mm.
Conservation
IUCN Red List status is Least Concern with a stable population trend. However, they are considered a major invasive threat in non-native regions where they outcompete and prey on native fauna, and they act as vectors for the amphibian chytrid fungus.
Description
The American Bullfrog is an impressive and formidable amphibian, reigning as the largest frog in North America. Sitting quietly among shoreline reeds with its golden eyes peering above the water line, it cuts a striking silhouette. Its booming call is an iconic soundtrack of warm summer nights across wetlands, reflecting its status as an apex predator of the shallows.
Key Features
Absence of dorsolateral folds on the back, massive tympanums (larger than the eye in males), uniform or mottled olive-green to brown upper body without prominent dorsal stripes, and a prominent skin fold curling around the eardrum.
Physical Description
Robust, stout-bodied frog with a broad, flat head. Large, prominent eyes with golden-brown irises and horizontal pupils. Highly visible, large circular tympanums (eardrums) located directly behind the eyes, noticeably larger in males than in females. Strong, muscular limbs with extensive webbing on the hind feet, but lacking the dorsolateral folds that run down the back in many other ranid species.
Skin Texture & Coloration
Skin is relatively smooth on the back but can be slightly granular or rugose posteriorly. Coloration typically ranges from olive-green to brown, often with dark spots or a mottled pattern on the back and limbs. The throat of breeding males turns bright yellow, while females have lighter, pale throats. The underside is white or cream, sometimes heavily mottled with gray or brown.
Distinguishing Features
Distinguished primarily by the complete absence of dorsolateral folds along the back (unlike the Green Frog, which it closely resembles), very large tympanums (larger than the eye in mature males), and a fold of skin that wraps entirely around the circular tympanum and extends down toward the arm.
Habitat
Found primarily in permanent freshwater bodies such as large ponds, lakes, swamps, and slow-moving rivers with abundant emergent aquatic vegetation. Prefers still or slow waters with muddy substrates and shoreline cover.
Geographic Range
Native to eastern and central North America, ranging from southern Canada down to the Gulf of Mexico and east of the Great Rockies. Widely introduced across western North America, South America, Europe, Asia, and various islands, frequently becoming an invasive species.
Behavior
Primarily nocturnal and crepuscular, though often active during overcast or rainy days. Highly aquatic and will leap into deep water when threatened, using powerful hind legs. Highly territorial males defend calling sites aggressively.
Diet & Feeding
Voracious apex predators in aquatic microhabitats. Diet includes insects, spiders, worms, crayfish, fish, snakes, birds, rodents, and other frogs. Uses a sit-and-wait ambush strategy, snapping up virtually any moving prey that fits into its exceptionally wide mouth.
Reproduction
Breeds from late spring to mid-summer, triggered by rising water temperatures and heavy rains. Males establish territories and emit loud calls to attract females. Females lay massive egg masses containing up to 20,000 eggs that float as a thin surface film on the water.
Vocalizations
Famous for its deep, resonant, foghorn-like 'jug-o-rum' advertisement call, which can carry over long distances across water bodies. Males also produce territorial squawks and release calls when grabbed by other males.
Life Cycle
Eggs hatch in 3 to 5 days into large, olive-green tadpoles speckled with black dots. The larval stage typically lasts 1 to 2 years (sometimes up to 3 years in northern climates) before undergoing metamorphosis into froglets. Sexual maturity is reached in 2 to 3 years.
Conservation Status
IUCN Red List status is Least Concern with a stable population trend. However, they are considered a major invasive threat in non-native regions where they outcompete and prey on native fauna, and they act as vectors for the amphibian chytrid fungus.
Toxicity & Defense
Non-toxic to humans, though their skin secretes mild defensive mucus that tastes foul to some predators. Primary defense is a powerful, explosive leap directly into deep water, often accompanied by a startling squawk.
Ecological Role
Acts as an apex predator in aquatic ecosystems, helping regulate insect, fish, and amphibian populations. Conversely, as an invasive species outside its native range, it heavily disrupts local food webs and native biodiversity.
Similar Species
Green Frog (Lithobates clamitans) is the most similar species, but can be distinguished by the presence of prominent dorsolateral folds running down the back. Pig Frog (Lithobates gryllus/capito complex) has a pointed snout.
Observation Tips
Best observed at night along the margins of ponds or lakes using a flashlight to catch the ruby-red eye shine. Approach slowly and quietly from the water side if possible, as they bolt instantly when disturbed.
Handling & Safety
Safe to handle, but should be done with wet hands to protect their delicate skin permeable membranes. Large adults possess a powerful grip and can deliver a surprisingly strong pinch with their jaws if mishandled.
Seasonal Activity
Active from spring through autumn. In colder northern climates, they undergo brumation during winter, burying themselves in the mud at the bottom of ponds or streams to overwinter.
Cultural Significance
Featured extensively in literature, folklore, and popular culture, most famously in Mark Twain's classic short story 'The Celebrated Jumping Frog of Calaveras County'. Also historically harvested on a large scale for frog legs.
Interesting Facts
Bullfrogs are notorious for their lack of dietary discretion and have been documented consuming birds, bats, small snakes, turtles, and even other bullfrogs. Their booming call can be heard up to half a mile away.