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The Problem with Bullfrogs

~Wildlife education~

The American bullfrog (Rana catesbeiana), the largest frog in North America, is an invasive species due to its voracious appetite and the large number of eggs it produces. It has a negative effect on native amphibians and other fauna.

Frogs eat any animal that can be captured and swallowed, including all kinds of vertebrates and invertebrates. Larvae eat suspended matter, organic debris, algae, plant tissue, and small aquatic invertebrates. Bullfrog adults eat insects, snakes, small mammals, birds, and smaller native frogs.

An American bullfrog

The bullfrog gets its name from the sound the male makes during the breeding season, which sounds similar to a bull bellowing. Amphibians like frogs, toads, newts, and salamanders live in the water but can survive on land. Many species of birds eat frogs, toads and salamanders. Long-legged wading birds like herons and egrets feast on these amphibians. The common merganser eats frogs and 5% of the belted kingfisher’s diet is frogs. Crows are also voracious eaters of frogs.

The belted kingfisher consumes the large tadpoles of the bullfrog when it dives into the shallows of small ponds, but it does not eat enough tadpoles to make a difference in the invasive population. The bullfrog is a successful breeder and can live up to 15 years. They begin breeding at the age of 4, with females laying up to 20,000 eggs in a single spawn. These tadpoles grow to about 15 cm. over a two-year period before they turn into a frog. They breed in early May in permanent ponds and lakes in sub-urban, rural, disturbed and wooded habitats. Sometimes they move into stream habitats either as tadpoles or young frogs. The bullfrog is the largest frog in North America, growing 8-20 cm. long and weighing up to 600 grams. They are green to brownish green in colour, and the breeding males have yellow under their chins. They have a conspicuous skin fold around the ear membrane down to the shoulder.

Native to North America from southern Quebec and Ontario to the Gulf of Mexico, bullfrogs have spread into western North American from southern British Columbia to California. To prevent their spread into new areas, please do not move frogs, tadpoles or frog eggs from one wetland to another.

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