Bullfrog (Rana catesbeiana) 



Description: The largest of North American frogs, adult Bullfrogs may reach 8 inches in snout- 

 vent length. The skin is smooth. Adults are usually pale to dark green or brownish green 

 with darker spots or blotches. There are a series of black bands across the legs. The 

 underside is cream to yellowish with gray mottling. No dorso-lateral folds are present, 

 however there is a prominent ridge running from the eye over the tympanum to the shoulder. 

 Males have extensive yellow pigment on the underside, especially in the throat region, and 

 swollen thumbs. The diameter of the tympanum is larger than the diameter of the eye in 

 males but about the same size in females. Egg masses consist of thousands of eggs and may 

 reach several feet across. Tadpoles may reach 4.5" in total length and are olive green with 

 numerous black spots dorsally. The belly is white to creamy with varying amounts of dark 

 mottling. Tadpoles usually take two or more years to metamorphose. 



Habitat and Habits: Bullfrogs are the most aquatic of Montana's amphibians, rarely being seen 

 far from the water's edge and usually in the water. They are associated with larger bodies of 

 quiet water such as ponds, lakes or backwaters of streams, usually with extensive emergent 

 vegetation such as cattails or reeds. They emerge in the spring only after air and water 

 temperatures have warmed considerably and insect populations are beginning to proliferate. 

 Breeding takes place in June when males attract females to their territory by a series of loud 

 brr-umps. The large mass of eggs tend to float on the surface when first laid, but sink into 

 the water prior to hatching (Hammerson 1982a, Nussbaum et al. 1983). Tadpoles over- 

 winter in the Pacific Northwest, transforming during their second summer (Nussbaum et al. 

 1983, Leonard et al. 1993). The bullfrog is a voracious feeder, eating anything smaller than 

 itself, including ducklings, fish, mice, frogs, and small turtles. Bullfrogs have been 

 implicated in extirpations of native frogs and turtles, and declines in waterfowl production 

 (Hammerson 1982b, Leonard et al. 1993). 



Surveying: Both tadpoles and adults can be sampled by using a dipnet. Capture success of adults 

 is enhanced by night sampling using a headlamp, as they are very wary and do not allow 

 close approach during the day. 



Status: Bullfrogs are native to the eastern and central U.S., and have been introduced to the 

 western states. They were introduced into western Montana prior to the 1960's. Viable 

 populations are scattered along the Flathead and Clark Fork Rivers as well as in the Bitterroot 

 Valley and possibly other localities. There is one known population on private land in the 

 Cabinet district of the KNF. 

 Montana Natural Heritage Program rank: G5 SE4 



21 



