Bullfrog
Rana catesbeiana
Summary: This is possibly the only local frog which is more common today than in presettlement times. Permanent bodies of water, including rivers, lakes, and farm ponds, are inhabited.
Description: This is easily the largest local frog; adults routinely reach six inches (15.2 cm), and the record size is eight inches (20.3 cm).
Bullfrogs are uniform olive green above, lighter green on the upper jaws, and white below. Large adults can be identified on size alone. Smaller individuals can be distinguished from green frogs by the absence of dorsolateral folds. The hind feet are webbed.
Distribution and Status: Bullfrogs may be the only local native amphibian which is more abundant today than it was in presettlement times. Robert Kennicott did not mention the species, even though his mid-1850s collections took place in parts of Cook County where bullfrogs are common today. This species has adapted to human modified habitats, and as a result it is widespread and is currently relatively common throughout the region.
Habitat: Bullfrogs are closely tied to permanent water, and most observations are of animals at the waters edge. Larger bodies of water, including large rivers and lakes are preferred. Man-made situations including farm ponds, quarry ponds, and ditches are frequently inhabited. Because these altered habitats are often structurally simple, with little cover at the land-water interface, smaller frogs (and other animals) are easy prey for large bullfrogs.
Voice: A deep bass note, "br-rrum."
Phenology: Breeding is prolonged, and occurs throughout the early summer. Eggs are deposited as large floating masses. The large tadpole requires almost two years to achieve metamorphosis. Sometimes they can be seen under the winter ice in shallow wetlands. Juveniles are common along shorelines in fall.
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| Updated: October 9, 2007
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