Invading bullfrogs will eat almost anything! (Thinkstock / Reuters)
Invading bullfrogs will eat almost anything!
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An invasion of American bullfrogs that will eat just about anything, including each other, is spreading downstream along Montana's Yellowstone River and poses a potential threat to native frogs, government scientists say.

Bullfrogs were found in surveys along a 66-mile stretch of the river from the Laurel area downstream to Custer, according to U.S. Geological Survey biologist Adam Sepulveda. The number of breeding sites for the frogs almost quadrupled between 2010 and last year, rising to 45 total.

"They are going to eat anything they can fit into their mouths. It doesn't matter if it's another frog or a bird or a mosquito," said Sepulveda, who co-authored a study on Yellowstone River bullfrogs appearing in the journal Aquatic Invasions.

Bullfrogs as long as 12 inches when outstretched have been found. One that was caught near the Audubon Conservation Center in Billings last year had a bird in its stomach.

State and federal agencies initially tried to stop the invaders in their tracks by killing them all off, but gave up after the number of bullfrogs overwhelmed the effort. They're now trying to come up with a strategy to at least contain their spread.

Bullfrogs are native to the eastern U.S., but are known to have been spread by humans to every state except North Dakota.

They've caused problems elsewhere by preying on native frogs, out-competing other animals for food, and spreading a fungus that's suspected as a cause of a widespread decline in amphibians, Sepulveda said.

They were first documented in eastern Montana in 1999. Scientists believe they descended from released pet frogs or bullfrog tadpoles used as bait by fishers.

The frogs have inhabited areas of western Montana since the 1920s, likely from a farming operation that sold their legs to be eaten, Sepulveda said.

Critical thinking challenge: Why do invading bullfrogs pose a threat to native frogs?

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COMMENTS (30)
  • SAlexander-Sti
    10/07/2014 - 10:03 a.m.

    Bull frogs across yellow stone are invading, they are eating almost anything they can fit in there mouth. Even if its each other they started invading in 2010. They can get up to 12 in long there's a total of about 45.

  • NashMcComsey-Ste
    10/07/2014 - 01:50 p.m.

    Invaisive species, even if they do come from our own soil, will always present an issue to native creatures. I wish to know, however, how much of a direct threat the bullfrogs are.

  • icegits
    10/07/2014 - 02:08 p.m.

    This is crazy!! So many bull frogs are here now. These frogs pose a threat to native frogs because they can eat all of the food for the native frogs. all of the frogs will starve, then we will be left with a bunch of fat frogs.

  • TaylorSeifert-Ste
    10/07/2014 - 02:44 p.m.

    This is the first time I have ever heard of a bull frog eating a bird, but I can imagine it happening. I haven't seen too many frogs in my life so it's weird to hear that the bull frogs population is spreading too quickly. I wonder how humans can contain small animals like bull frogs in the wild. It's not like they can just put up a fence and say the job is done.

  • ShaniaWentz-Ste
    10/08/2014 - 09:11 a.m.

    Honestly, this is a pretty scary thing. Bullfrogs that eat other bullfrogs are very strange. I have never heard of anything like this. I hope that we can get this under control so that it doesn't get too out control.

  • smt0415love
    10/09/2014 - 08:40 a.m.

    Because invading bullfrogs eat almost everything they even eat other frogs such as native frogs. If the invading bullfrog lives on the environment of the native frogs the native frogs population would decrease

  • PJuan-Sti
    10/09/2014 - 10:51 a.m.

    This is crazy! I cant believe that they eat birds and there own kind. They eat what ever fits on there mouth.
    bullfrogs ha sent been spread out in North Dakota.

  • MikaylaStazewski-Ste
    10/09/2014 - 01:06 p.m.

    The fact that american bullfrogs will eat each other honestly makes me feel some type of way. That is just crossing the line in my eyes.

  • meredithkirbo
    10/09/2014 - 01:11 p.m.

    Bull frogs are really cool amphibians. That is really cool they can in eat birds and things bigger than them. I know if i was a frog i would not be able to eat things bigger than me!

  • TreyvaunT
    10/09/2014 - 01:27 p.m.

    I think that it is pretty crazy that they eat there own kind. That means that they are a cannibal. I never knew that bullfrogs eat frogs

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