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The native range of the American Bullfrog lies east of the Continental Divide and extends from Canada south into Mexico; introduced populations now exist west of the divide and can be found in expanding regions or in small isolated pockets along the coast and into the Rocky Mountains below 6,000 feet. In Wyoming their native range has extended up the North Platte River to Douglas and up the Laramie River past Wheatland; an introduced population exists at a warm springs near Kelly. They are found in the permanent water of ponds, sloughs, and irrigation canals at the lower elevations of the prairie life zone—especially where the substrate is smothered with a layer of deep, soft muck, where the water is choked with aquatic life and thick mats of algae, and where the margins are obscured with dense growths of rushes, cattails, and overhanging vegetation. They are a highly aquatic species and spend most of their life in or near water where, acting as wholesale carnivores, they feed on insects and crayfish, as well as small vertebrates like mice, birds, snakes, and other frogs.
The bullfrog is the largest species of amphibian residing in Wyoming and lengths can sometimes reach 6 inches (SVL). They are strong and muscular, and, being extremely wary and known for their leaping abilities, they are quite difficult to catch. Their skin is moist and smooth, though they do show some glandular imperfections that resemble the small pimples of a rash. The dorsal surface is mottled (sometimes faintly so) with black irregular bands and displays a gradient in color, from the brown or dark green of the hind quarters to the lighter and more striking green on the head. The ventral surface is white or pale yellow with darker marbling and vermiculations. They lack the dorsolateral fold (a pucker of skin forming a delineation between the back and the sides) of other species of frogs found in Wyoming, but they do enjoy a prominent furrow of skin that extends from behind the eye, runs around the top of the tympanum, and terminates on the shoulder. The tympanum of adult males is much larger than the eye; in females and juveniles it is about the same diameter of the eye.
Breeding takes place in July and August and is initiated by sultry temperatures rather than seductive rains. The bellowing “brruumm” call of the male is created in the vocal sac of a bright yellow throat patch and is issued as an advertisement call. Males defend their territories with guttural calls, threatening postures or advances, and with physical assaults and wrestling bouts. A female is clasped in amplexus (lasting a couple of hours) aided by the enlarged and roughened nuptial pads on the male’s thumbs. The eggs are fertilized as they are released from her body and are spewed on the water’s surface—forming a floating film of jelly that is several layers deep, 3-4 feet in diameter, and containing many thousands of eggs. The eggs eventually sink to the bottom and hatching occurs in 3-5 days. The resulting tadpoles swim and feed during the remaining summer and fall; they then burrow into the muck and remain dormant overwinter. Their larval growth continues during the following spring and they undergo metamorphosis after reaching lengths of three or more inches. When startled, juveniles emit an “eep eep” as they scramble across mats of algae. Sexual maturity is reached 2-3 years after metamorphosis.