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Giant invasive frogs are wreaking havoc on the West
Giant invasive frogs are wreaking havoc on the West

Vox

time4 days ago

  • General
  • Vox

Giant invasive frogs are wreaking havoc on the West

is an environmental correspondent at Vox, covering biodiversity loss and climate change. Before joining Vox, he was a senior energy reporter at Business Insider. Benji previously worked as a wildlife researcher. On summer evenings in the Midwest, the muggy air comes alive with a chorus of crickets, cicadas, and frogs — especially bullfrogs. Their booming mating calls sound like something between a foghorn and a didgeridoo. As far as we know, summer here has always sounded like this. Bullfrogs are native to most of the Eastern US, from the Mississippi River to the Atlantic Coast. They evolved here. They belong here. I, for one, adored them as a kid growing up in Iowa, and spent countless summer days trying to catch them to get a closer look. What's unusual is that a few states west — into Colorado and on to California — summer nights are similarly marked by the iconic call of the American bullfrog. But here, they don't belong. They're unwanted. And they threaten the very existence of some of the West's other amphibious animals, such as the Oregon spotted frog, which is found only in the Pacific Northwest. An American bullfrog tadpole next to a juvenile northwestern pond turtle. Courtesy of Sidney Woodruff American bullfrogs are not native to the Western US. Humans brought them to the region more than a century ago, largely as a food source. And in the years since, the frogs — which are forest green and the size of a small house cat — have multiplied dramatically, spreading to countless ponds and gobbling up everything that fits in their mouths, including federally threatened and endangered species. Conservation scientists now consider them among the most dangerous invasive species in the Western US, and in the 40-plus other countries worldwide where they've been introduced. That leaves bullfrogs in an unusual position. Invasive species are typically brought in from other countries — Burmese pythons in Florida and spotted lanternflies in New York City come from Asia, for example — but American bullfrogs are, as their name suggests, American. They're both native and invasive in the same country. And the difference of just a few states determines whether we treat them like pests or as an important part of the ecosystem. It's easy to hate bullfrogs. They do cause a lot of damage and, like other non-native species, they're leading to what some researchers call the Starbucksification of the natural world — you find the same thing everywhere you go, which can make ecosystems less resilient. Yet bullfrogs themselves aren't the main problem, but rather a symptom of a much bigger one. How bullfrogs took over the West One reason is that people enjoy eating them. Or more specifically, their legs. In the 1800s, as the human population in the West surged amid the Gold Rush, so did an appetite for frog legs, which were associated with fancy French cuisine. To meet that demand, people collected native amphibians from the wild, like the California red-legged frog. But as those species became rarer and rarer — in part, due to overharvesting, researchers suspect — entrepreneurs and farmers started importing American bullfrogs from the eastern US and tried to farm them. For a time, it seemed like the bullfrog industry might take off. 'Bullfrog legs! Something to tickle the gustatory glands of the epicurean bon vivants,' a reporter wrote in the Riverside Daily Press, a California paper, in 1922. 'Propagation of the bullfrog in this state already has become a successful reality. In the near future, bullfrog farming may be expected to take its rightful place as one of the prominent industries of California.' That never really came to pass. Bullfrog farming proved challenging and financially risky: They take years to raise, they need loads of live food, and they're prone to disease outbreaks, as Sarah Laskow wrote in Atlas Obscura. And for all that trouble, they don't produce much meat. A bullfrog in the water at a golf course in Fort Worth, while the frog leg industry didn't spread, the frogs, of course, did. They escaped from farms and, with other accidental and intentional introductions, proliferated until they were common in ponds, lakes, and other water bodies throughout much of the West, including Arizona, California, and the Pacific Northwest. Now, in some portions of the region, 'you see so many bullfrogs that it's just sort of alarming,' said Michael Adams, an amphibian researcher at the US Geological Service, a government research agency that monitors wildlife. There are no reliable estimates of the total population of bullfrogs in the West, though a single pond can be home to thousands of individuals. Part of what enabled their success is biology: A female bullfrog can lay as many as 25,000 eggs at one time, far more than most native species. But as several researchers told me, humans have also modified the landscape in the West in ways that have helped bullfrogs take over. While western states have rivers and wetlands, permanent warm waterbodies weren't common until the spread of agriculture and the need for irrigation, said Tiffany Garcia, a researcher and invasive species expert at Oregon State University. Now ponds, reservoirs, and canals — which bullfrogs love — are everywhere. 'It's a story of human colonization,' Garcia said. 'Bullfrogs were brought by people settling and industrializing the West, and they are maintained by people who are natural-resource users of the West. They wouldn't be here and survive without us changing the landscape to create these systems where they do so well.' Bullfrogs are often found alongside other non-native species, Garcia said, which typically tolerate landscapes modified by humans. And sometimes they even help each other succeed. Research has, for example, shown that bluegill sunfish — introduced in the West largely for sportfishing — can help bullfrogs survive. Sunfish will eat dragonfly larvae that might otherwise prey on bullfrog tadpoles. 'You can't even consider them invasive species anymore,' Garcia said of bullfrogs. 'You have to consider it an invasive community.' Bullfrogs are bullies Like unsupervised toddlers, bullfrogs will put pretty much anything in their mouths. Mice, birds, turtles, snakes, rocks, other bullfrogs — if it fits, they'll try to eat it. This is a big problem for species that are already rare, such as the Chiricahua leopard frog or the northwestern pond turtle. Bullfrogs are shrinking their paths to extinction. 'They're implicated in the declines, along with habitat loss and drought, of many of our native reptile and amphibian species,' said Sidney Woodruff, a doctoral researcher at the University of California Davis who studies bullfrogs and other invasive amphibians. In May, Woodruff published a study that found that waterbodies in Yosemite National Park that were full of bullfrogs had lower densities of northwestern pond turtles than those without invasive frogs. She also found that where bullfrogs were present, only large turtles could survive. A northwestern pond turtle in Yosemite National Park. Courtesy of Sidney Woodruff 'Our study adds mounting evidence that hatchling and juvenile pond turtle losses to bullfrogs pose a serious threat to pond turtle population persistence,' Woodruff and her co-authors wrote. And where bullfrogs live in communities with other invasive species, native animals often face even greater challenges, said JJ Apodaca, executive director of the Amphibian and Reptile Conservancy, a nonprofit environmental group. Non-native crayfish, for example, are voracious consumers of plants and other habitat features that native animals hide in. So, where you have invasive crayfish, the local fauna will be that much easier for bullfrogs to eat. Invasive bullfrogs may also be spreading diseases. A study published in 2018 linked the arrival of bullfrogs in the West with the spread of a pathogen called chytrid fungus. While the pathogen typically doesn't sicken bullfrogs, it has helped drive the decline and extinction of more than 200 amphibian species globally, including those in the West. Okay, so let's kill all the bullfrogs? No, a bullfrog-killing spree won't fix ecosystems in the West. They're already everywhere, so even if scientists manage to eliminate them from a pond or 10 ponds — which often requires fully drying out the water body and hours and hours of effort — they'll likely come back. 'It's futile,' Garcia said. 'We're not getting rid of bullfrogs. Not really.' Even if we could remove bullfrogs from large areas in the West, ecosystems wouldn't suddenly revert back to some sort of natural state. Bullfrogs are both a problem themselves and a symptom of change — of the large-scale transformation of land in the West. 'There's kind of an irony,' said Brendon Larson, a researcher and invasive species expert at the University of Waterloo. 'We're nurturing these agricultural systems — which are monocultures and non-native species — and then we're turning around and saying we're surprised when a non-native species does well in response to that.' Doing nothing isn't a great option either. Left alone, bullfrogs will continue to replace native species that comprise the ecosystems we depend on, including insects that pollinate our crops and salamanders that can help limit the amount of carbon dioxide entering the atmosphere and accelerating climate change. An American bullfrog in Yosemite National Park. Yosemite National Park Service The best approach, researchers told me, is to prioritize bullfrog control — to get rid of frogs in areas with endangered species or where conservation scientists are reintroducing native species that disappeared. This works. For her study on pond turtles earlier this year, Woodruff and her colleagues caught more than 16,000 bullfrogs across two waterbodies in Yosemite — using nets, spears, air rifles, and other methods — which they then euthanized. It was only after her team shrank the invasive frog population that they detected small, baby pond turtles in those areas. That suggests that, absent bullfrogs, the turtles were finally able to breed and survive, 'providing some hope for turtle population recovery once bullfrog predation pressures are alleviated,' the researchers wrote. Woodruff says she noticed all kinds of other native animals return after clearing out the invasive bullfrogs, including native frogs, salamanders, and snakes. 'The coolest thing to me was that the soundscape changed,' she told me. 'Over time, you actually started to hear our native chorus frogs again.' Managing bullfrogs is complicated, Woodruff says, and especially for her. She grew up in Alabama and Georgia, where the animals are native. She liked hearing them. But now she lives in California, where she's studying how they harm the environment, and so hearing them makes her tense up.

Invasive bullfrogs ‘eat everything' — including turtles — at Yosemite, study says
Invasive bullfrogs ‘eat everything' — including turtles — at Yosemite, study says

Miami Herald

time11-06-2025

  • Science
  • Miami Herald

Invasive bullfrogs ‘eat everything' — including turtles — at Yosemite, study says

A study has found that removing invasive bullfrogs from Yosemite National Park ponds has generated a resurgence in the population of native pond turtles, experts said. When University of California, Davis, researchers first began studying four ponds at the park, they were overwhelmed by non-native American bullfrogs, a news release said. 'At night, you could look out over the pond and see a constellation of eyes blinking back at you,' said Sidney Woodruff, a UC Davis Ph.D. candidate and lead author of the study. 'Their honking noise is iconic, and it drowns out native species' calls.' The invasive frogs had decimated the native population of northwestern pond turtles, according to the study, published in the May issue of the journal Biological Conservation. Together with the southwestern pond turtle, northwestern pond turtles are the only native freshwater turtles in California, the university said. Northwestern pond turtles have vanished from over half their range, which stretches from Baja California to Washington state. At Yosemite, the only surviving turtles in the ponds surveyed were the ones that were too big for bullfrogs to eat, the study found. American bullfrogs are native to the eastern United States but don't belong in the West. 'One reason American bullfrogs are among the top worst globally introduced pests is because they eat everything — anything that fits into their mouth,' said senior author Brian Todd, a UC Davis professor in the Department of Wildlife, Fish and Conservation Biology. 'They've been causing declines to native species everywhere they're introduced, which is around the world.' The bullfrogs were introduced to Yosemite National Park in the 1950s and quickly spread throughout the park, researchers said. While their arrival was believed to be linked to the decline in pond turtles, it wasn't confirmed until the study took place, according to researchers. Between 2016 and 2022, researchers monitored four ponds at Yosemite, two with bullfrogs and two without, the study said. Turtles were 2 to 100 times more prevalent at the ponds where bullfrogs were absent, researchers said. When bullfrogs were removed from the other two ponds in 2019, researchers found juvenile pond turtles in them for the first time, the study said. 'As bullfrog presence declined, we started to hear other native frogs call and see native salamanders walking around,' Woodruff said. 'It's nice to be able to go back to these sites and hear a chorus of native frogs calling again that previously would not have been heard.' The Western Pond Turtle Range-wide Conservation Coalition, Yosemite Conservancy, U.S. Geological Survey and USDA National Institute of Food and Agriculture funded the study.

Native turtles return to Yosemite after removal of more than 16,000 invasive bullfrogs
Native turtles return to Yosemite after removal of more than 16,000 invasive bullfrogs

USA Today

time29-05-2025

  • Science
  • USA Today

Native turtles return to Yosemite after removal of more than 16,000 invasive bullfrogs

Native turtles return to Yosemite after removal of more than 16,000 invasive bullfrogs As part of the study, 16,384 American bullfrogs, larvae and egg masses were removed from Yosemite National Park. Show Caption Hide Caption Yellow-legged frogs make comeback in Sierra-Nevada lakes Non-native fish and the amphibian chytrid fungus nearly wiped out the yellow-legged frogs in the lakes of the High Sierra at Yosemite National Park. A "constellation of eyes" welcomed Sidney Woodruff the first time she went nighttime frog spotting at Yosemite National Park. Her headlamp lit up thousands of eyes that belonged to the invasive American bullfrog, peering up at her from where they lurked in the water. Woodruff, a PhD candidate at University of California, Davis, is the lead author of a recently-published study that analyzed how the removal of American bullfrogs affected the population of native northwestern pond turtles at Yosemite National Park. Over the course of six years, Woodruff and her team removed more than 16,000 American bullfrogs from the park − an invasive species that makes life for the northwestern pond turtle nearly impossible. But now, with less frogs in the midst, the native turtle is reappearing at the park. "We focused on the impact to turtles, but anecdotally, we're out there and can see the change and response in the environment," Woodruff told USA TODAY. "It's really exciting to see that, see what these sites should look like." 'The lakes are alive again': These frogs are back from near extinction Vacation planning: What is the No. 1 national park? Here are the 10 most (and least) visited in 2024. When, why did the American bullfrog invade Yosemite? Native to the eastern United States, American bullfrogs were intentionally introduced to Yosemite in the 1950s, with the first bullfrog documented in The Ahwahnee Hotel's reflection pond in 1955, according to the U.S. Fish and Wildlife Service. Yosemite isn't the only victim of American bullfrogs' invasive nature. In fact, the bullfrog is one of the top 100 world's worst invasive species, according to the Global Invasive Species Database. How do American bullfrogs affect pond turtle populations? American bullfrogs are a "highly successful invasive species," Woodruff said. This is due to their size and particularly, their stomachs. Bullfrogs, which can weigh 2-3 pounds, are adaptable and known for eating a variety of prey, including insects, crustaceans, other amphibians, reptiles, fish, small birds and mammals, Woodruff's study outlines. If it fits in their mouth, they'll eat it. During her research, Woodruff reported numerous instances of small pond turtles found inside American bullfrog stomachs. And the pond turtles that were in the habitats were old and large, indicating that they only survived because they wouldn't fit in the frogs' mouths. How were the American bullfrogs removed from Yosemite? Woodruff's team studied and removed American bullfrogs in areas between Yosemite's Lake Eleanor and Hetch Hetchy Reservoir, which are about 40 miles north of Yosemite Valley. Woodruff said there were three ways her team removed the bullfrogs from the park: Catching the frogs from shore, riding inflatable boats out to catch frogs further in the water and collecting egg masses from the water. In total, Woodruff and her team collected and removed 16,384 bullfrogs, larvae and whole egg masses from Yosemite, the study states. Once removed, the frogs were "humanely euthanized," Woodruff said. "It is very unfortunate with invasive species work, particularly when you are dealing with the numbers we had," Woodruff said. "There's just no other solution, unfortunately." What's happening now? What's next? The sites where Woodruff and her team removed the bullfrogs are "completely different," she said. Northwestern pond turtle hatchlings and youth are swimming about, the native California red-legged frog has reappeared and several other native species are back − ones that would have previously been eaten up by bullfrogs. Woodruff said the National Park Service is continuing the monitor the areas and their habitats and more bullfrog extraction may occur in the future. Greta Cross is a national trending reporter at USA TODAY. Story idea? Email her at gcross@

Native turtles return to Yosemite after removal of over 16,000 invasive bullfrogs
Native turtles return to Yosemite after removal of over 16,000 invasive bullfrogs

USA Today

time29-05-2025

  • Science
  • USA Today

Native turtles return to Yosemite after removal of over 16,000 invasive bullfrogs

Native turtles return to Yosemite after removal of over 16,000 invasive bullfrogs As part of the study, 16,384 American bullfrogs, larvae and egg masses were removed from Yosemite National Park. Show Caption Hide Caption Yellow-legged frogs make comeback in Sierra-Nevada lakes Non-native fish and the amphibian chytrid fungus nearly wiped out the yellow-legged frogs in the lakes of the High Sierra at Yosemite National Park. A "constellation of eyes" welcomed Sidney Woodruff the first time she went nighttime frog spotting at Yosemite National Park. Her headlamp lit up thousands of eyes that belonged to the invasive American bullfrog, peering up at her from where they lurked in the water. Woodruff, a PhD candidate at University of California, Davis, is the lead author of a recently-published study that analyzed how the removal of American bullfrogs affected the population of native northwestern pond turtles at Yosemite National Park. Over the course of six years, Woodruff and her team removed more than 16,000 American bullfrogs from the park − an invasive species that makes life for the northwestern pond turtle nearly impossible. But now, with less frogs in the midst, the native turtle is reappearing at the park. "We focused on the impact to turtles, but anecdotally, we're out there and can see the change and response in the environment," Woodruff told USA TODAY. "It's really exciting to see that, see what these sites should look like." 'The lakes are alive again': These frogs are back from near extinction Vacation planning: What is the No. 1 national park? Here are the 10 most (and least) visited in 2024. When, why did the American bullfrog invade Yosemite? Native to the eastern United States, American bullfrogs were intentionally introduced to Yosemite in the 1950s, with the first bullfrog documented in The Ahwahnee Hotel's reflection pond in 1955, according to the U.S. Fish and Wildlife Service. Yosemite isn't the only victim of American bullfrogs' invasive nature. In fact, the bullfrog is one of the top 100 world's worst invasive species, according to the Global Invasive Species Database. How do American bullfrogs affect pond turtle populations? American bullfrogs are a "highly successful invasive species," Woodruff said. This is due to their size and particularly, their stomachs. Bullfrogs, which can weigh 2-3 pounds, are adaptable and known for eating a variety of prey, including insects, crustaceans, other amphibians, reptiles, fish, small birds and mammals, Woodruff's study outlines. If it fits in their mouth, they'll eat it. During her research, Woodruff reported numerous instances of small pond turtles found inside American bullfrog stomachs. And the pond turtles that were in the habitats were old and large, indicating that they only survived because they wouldn't fit in the frogs' mouths. How were the American bullfrogs removed from Yosemite? Woodruff's team studied and removed American bullfrogs in areas between Yosemite's Lake Eleanor and Hetch Hetchy Reservoir, which are about 40 miles north of Yosemite Valley. Woodruff said there were three ways her team removed the bullfrogs from the park: Catching the frogs from shore, riding inflatable boats out to catch frogs further in the water and collecting egg masses from the water. In total, Woodruff and her team collected and removed 16,384 bullfrogs, larvae and whole egg masses from Yosemite, the study states. Once removed, the frogs were "humanely euthanized," Woodruff said. "It is very unfortunate with invasive species work, particularly when you are dealing with the numbers we had," Woodruff said. "There's just no other solution, unfortunately." What's happening now? What's next? The sites where Woodruff and her team removed the bullfrogs are "completely different," she said. Northwestern pond turtle hatchlings and youth are swimming about, the native California red-legged frog has reappeared and several other native species are back − ones that would have previously been eaten up by bullfrogs. Woodruff said the National Park Service is continuing the monitor the areas and their habitats and more bullfrog extraction may occur in the future. Greta Cross is a national trending reporter at USA TODAY. Story idea? Email her at gcross@

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