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American Bullfrog

Rana catesbeiana

Identifying Characteristics

  • up to 20 cm long
  • olive/yellow with grey belly
  • males have bright yellow throats during mating season
  • very large ear drums (tympanic membranes)
  • the skin fold is wrapped around the ear drum, but there are no ridges down the back

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American bullfrog.mp3

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This is a photograph of an American Bullfrog on a log. 4 images
This is a map of British Columbia showing the spread of invasive species.

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(Video 1:30 3.85 MB)

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Video transcript

Alien Invaders
This is a photograph of frog specimens in a jar.
Once upon a time, museum researchers used to focus more on collecting and displaying living things than on interpreting patterns in nature.  

Hi, I’m Connie Mitchell, here with Gavin Hanke from the Royal BC Museum. Gavin’s curator of vertebrate zoology.  

Gavin, what are we doing here in the middle of this park?

Well, you can’t make a good museum display without new information and this can be found even in a city park.  

What new information are we going to find in the middle of this duck pond?

What about this?
This is a photograph of curator Gavin Hanke and Connie Mitchell with a turtle.
Wait a sec, I actually know that, that’s a Red-eared Turtle.

This is a photograph of curator Gavin Hanke holding a Red-eared Turtle.

I didn’t know they were from southern British Columbia.

They’re here now, yeah.

What do you mean?

These are exotic animals. These were normally found in the Mississippi River.  They’ve been dumped here, these are unwanted pets. Most people don’t realize the damage that they can cause.  

Let’s have a look over here.

Good idea.

And here’s a bullfrog.

This is a photograph of Gavin Hanke holding an American Bullfrog.

Exotic species like these threaten the environment when they spread outside of cities.  

I imagine natural change is inevitable, but releasing unwanted pets is just wrong in more ways than we can imagine.  

BC’s unique environment becomes less so with every exotic species that gets released.  We should do what we can to prevent the release of exotics, especially pets.

www.royalbcmuseum.bc.ca.

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A failed frog leg industry and a voracious eater threaten native frogs.

The American Bullfrog, is the largest of the North American frogs - it can grow to the size of a dinner plate and half a kilogram, and have an appetite to match its size. Bullfrogs will voraciously eat native species, including frogs, snakes, insects, small turtles, birds and mammals - anything they can catch in their large mouths. Bullfrogs are found in freshwater ponds and lakes across southern Vancouver Island, some Gulf Islands and the Lower Mainland. Adult males have a distinctive and booming "jug-o'-rum" call that can be heard around lakes and ponds in the late spring and summer.

Impact on Communities and Native Species

Bullfrogs are bad news for native frog species. The Bullfrog is not only a glutton, eating native frogs, but it also reproduces rapidly and pushes other species from its habitat. A single female frog can lay an egg mass containing up to 20,000 eggs. Bullfrogs also spread a fungal infection that doesn't harm the Bullfrog, but kills other newly exposed frogs. In their native habitat, Bullfrogs have predators such as bass, pike and snapping turtles that keep them in check, but in British Columbia, the usual frog predators find the tadpoles unpalatable and the large adult frogs too big to eat.

Invasion History

Bullfrogs were introduced to supply a frog leg industry that never took off. Frog farms were promoted after World War II as an entrepreneurial venture for returning veterans. The farms, however, didn't make a profit, and the Bullfrogs were released into the wild - and they flourished. Bullfrogs were also imported for sale by aquatic garden supply companies and escaped their backyard ponds. Tadpoles are sometimes inadvertently imported with goldfish shipments and raised by well-meaning pet owners who might not realize their impact.

Even schools can order bullfrogs and tadpoles from biology supply companies, and we can only hope that classes do not release adult frogs when the lesson is over.