The U.S. Geological Survey is tracking the spread of an invasive species, the American bullfrog, in Montana and Grand Teton National Park. They’re using genetics to determine where the species originated so they can manage their numbers.

Research zoologist Adam Sepulveda says, bullfrogs are a huge threat to other amphibian species, like the Columbia spotted frog, the boreal chorus frog and the Western tiger salamander, and could eventually become a threat to the extremely endangered Wyoming toad in the Laramie Basin.

“Bullfrogs are incredibly aggressive and they will eat just about anything that they can get into their mouths,” he says. “In Grand Teton, we looked at the diets of bullfrogs and we actually found a surprising amount of things like shrews and voles and mice in the stomachs of adult bullfrogs.”

Worst of all, bullfrogs carry the chytrid fungus which is wiping out amphibians worldwide.

Sepulveda says, this information will allow wildlife agencies to develop stricter import regulations to stop the spread of bullfrogs. He says, recently, their numbers have skyrocketed.

“The population in the Yellowstone River has been there since at least 1999. And it’s been spreading like crazy over the last ten years. They’ve gone from, I think it was nine sites that were documented in about 2010 to 57 sites in 2015.”

Sepulveda says, their study confirms that the bullfrogs have been imported into Western Wyoming from pet stores or as fish bait from out of state, although the species is native to the North Platte River in the east.

Currently, Wyoming doesn’t have a specific rule banning the American bullfrog. Sepulveda says bullfrogs are less widespread here, perhaps because there are fewer golf courses, community fishing ponds and other permanent water sources where they can breed.