By Kelly Werthmann

BOULDER COUNTY, Colo. (CBS4)– If you know where to look in Colorado, chances are you’ll see an American bullfrog. Unfortunately, they aren’t supposed to be here.

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“You can find them near ponds, small likes and reservoirs. They especially like places that are shallow on the edges,” Mac Kobza, a Boulder County Wildlife Biologist, explained. “They generally are dark green with a yellowish belly with spots.”

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Kobza has found hundreds of them recently as part of his work to control the bullfrog’s population in Colorado.

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“They don’t have any really good natural enemies around here,” he told CBS4. “That’s made worse because the tadpole aren’t really palatable to fish, so the young just tend to survive and grow into bigger numbers. Their numbers grow out of control.”

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American bullfrogs are not native to Colorado. They’re typically found in eastern and southern parts of the United States. Kobza said the species likely made its way into the Centennial state as a gaming species or maybe by accident while stocking fish in area lakes.

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“They’re also released as pets,” he said. “Bullfrogs are sold in the pet trade.”

While the bullfrogs appear harmless, they can easily devour bigger creatures.

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“They will eat whatever fits in their mouth,” Kobza explained. “Other frogs, snakes, and as they get even larger, they’ll eat birds, small mammals.”

The bullfrogs are also preying on protected and threatened wildlife, like the Preble’s meadow jumping mouse and northern leopard frog.

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“Unless we do something to control invasive wildlife, we’re going to lose our native wildlife,” Kobza said of the bullfrogs. “They also generally carry with them a thing called chytrid fungus. That is one of the worse diseases affecting amphibians worldwide.”

To curb the issue, wildlife experts like Kobza are removing several American bullfrogs from the region. Biologists in Boulder County use an electric rod to administer a low-dose voltage to stun the frogs first. Then they’re collected with nets before they’re euthanized.

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“They are humanely euthanized with Orajel. They go to sleep,” Kobza said.

That’s right. The same medication to treat mouth pain can effectively kill a bullfrog.

“[The frogs] are preserved and we donate them to the St. Vrain Valley School District for use in their science classes for dissection,” Kobza said.

Kobza explained biologists aren’t trying to eliminate every bullfrog in Boulder County, rather they’re doing what’s best to preserve the natural ecosystem.

“This is just one method that we can use to achieve that goal,” he said.

Kelly Werthmann


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