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Bull Frog

Rana catesbeiana Shaw

Bull Frogs are our largest frog. They are found in quiet coves of lakes with lots of vegetation, especially water lilies. Most are green or yellow-green, but rarely a blue Bull Frog (lacking yellow pigment) turns up.

Bull Frogs are the last amphibians to emerge in spring. Their booming bass call is heard from mid-June to July, although last year's tadpoles may emerge a month or two earlier. Males move out from shore and settle among the water lilies to call females. Spawning takes place soon after the females are grasped by males. She extrudes her eggs in a huge, film-like mass on the surface among the water lilies. Bull Frogs produce as many as 20,000 eggs each year. The tadpoles take two years to develop into young Bull Frogs; hind legs appear after the second winter. Tadpoles hibernate in the deep silt of the lake bottom.

The Bull Frog season is short. By early September most are hibernating in muddy pond bottoms. The Bull Frog menu includes birds, other frogs, fish, even their own tadpoles, as well as the usual insects. When held by the hind legs, Bull Frogs may let out a startling scream or squeal.

Additional Facts and Details

The family Ranidae of typical frogs consists of 45 genera and 586 species and is distributed nearly worldwide.

The genus Rana is represented in the Maritimes by 6 species in New Brunswick and Nova Scotia, while 3 occur on Prince Edward Island.

The toes on the front legs are unwebbed.

Breeding males can be told from females by the swollen base of the thumbs on the forelegs. This is related to the tight holding they do during amplexus.

Rarely, a Bullfrog is found which is partly blue instead of green. The green frog colour is a combination of structural blue and a yellow pigment; if the yellow is absent, the blue shows brightly.

Size: body length of 31 newly transformed young ranged from 4.4 to 5.4 cm. Length of 17 breeding males ranged from 10.1 to 14.8 cm. Length of 10 females ranged from 10.2 to 13.3 cm.

Distribution in Canada: mainland Nova Scotia, southern New Brunswick, southern Quebec, southern Ontario. There are several populations in southern British Columbia which were established from introductions. In the United States, south to Florida and west to the Rocky Mountains. There have been a lot of introductions, including to Mexico, Cuba and Jamaica.

In Nova Scotia, Bullfrogs are common in the Cumberland lowlands and inland from the spruce-fir coast of the southern mainland (mostly west of Highway 102). Common at a few localities in the St. Mary's River watershed. Probably occur in a few other local pockets northeast of Halifax. There are no records of Bullfrogs from Cape Breton Island.

The overwintering tadpoles become active in spring before the adults do. Earliest record for tadpoles is April 10, in 1951, in Caledonia, Queens County. Earliest record for a juvenile is April 15, 1972, at Colpton in Lunenburg County. Earliest record for an adult is May 4, 1983, an adult female at New Grafton, Queens County.

Overwintering tadpoles, after two winters, have a combined body and tail length as long as the body length of the largest adults. These are the really big tadpoles you may see.

Adult Bullfrogs eat a lot of other frogs.

The stomachs of many Bullfrogs studied were parasitized by nematode worms.

The latest record for an active adult Bullfrog is August 23, 1970, from Tomahawk Lake in Halifax County. Latest tadpole record is August 24, 1950, from Wigmore Lake in Cumberland County. Adults and juveniles are probably active in early September in the south-central mainland.