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Bullfrog

(Rana catesbeiana)

Identification: Upper side green or brown, usually with dark spots or mottling (but not large rounded spots); eardrum large, with fold of skin curving around top and rear edges; hind toes fully webbed; no ridges alongside of back; head and body length rarely more than 20 cm (7.9 inches) long.  

Mature male: Eardrum usually distinctly larger than eye (same diameter in female and young); throat yellow in breeding season; base of innermost toe on front feet swollen; expansion of the internal vocal sac causes a bulging of the throat.

Juvenile: Upper side green with many scattered small black dots.    

Breeding call : A deep bellowing “um-rum” or “um-er-rum” or similar vocalization.  

Larvae: In large individuals, upper surface green with small, black sharp-edged dots (dots also on tail fin); upper side black with gold crossbands in individuals less than 2.5 cm (1 inch) long; usually 1-3 rows of tiny teeth on upper lip, 3 rows on lower lip; up to about 18 cm 7 inches) long, commonly more than 10 cm (3.9 inches).

Eggs: Deposited in flat jelly masses up to more than 1 m (3.3 feet) in diameter and containing thousands of eggs (mass initially floats at surface of water but soon sinks).  

Colorado Distribution: Not native. Widely distributed in eastern Colorado, increasing range in river valleys of western Colorado; also present in San Luis Valley and in some warm waters in the mountains.    

Habitat: Typically in permanent ponds, reservoirs, quiet stream pools, and large, deep marshes. Also in flowing streams and irrigation ditches if the current is not too swift. Primary habitat often includes areas of deep water, cattails, and woody vegetation overhanging the water’s edge. Juveniles can be found in all kinds of aquatic habitats.   

Life History: Breeds in late spring or summer in warm, permanent water usually containing thick growths of algae and aquatic plants. Larvae overwinter at least once, then metamorphose into small frogs in spring or summer.