Meet San Francisco’s Newest (and Most Viral) Invasive Species

The potential sighting of a large American bullfrog in SF’s Golden Gate Park has set off alarm bells for ecologists.

San Francisco is no stranger to alien flora in fauna. After al., the City’s official animal is an invasive parrot from South America that began taking permanent roost sometime in the early 1990s. The initial two pairs of escaped (or intentionally released) cherry-headed conures lucked out, managing to find an ecological niche on Telegraph; now, there are an estimated 200 cherry-headed conures in San Francisco. But because of their lack of genetic diversity, these birds are susceptible to genetic defects; the ingested rat poisoning that threatened many of their lives a few years ago was an unrelated illness to their inbreeding; we humans were at fault for that.

I love seeing big 'ol tadpoles with TEENY TINY FEETS. This is an American bullfrog tadpole on it's way to frogdom. Although bullfrogs are terrible #invasive species in many parts of the world due to global food and pet trade, they are native here in the Southeastern US pic.twitter.com/PbsGWDTLVu

— Arik Hartmann (@AmphibiArik) February 21, 2020

But SF is home to far more than just foreign birds. Eastern gray and fox squirrels climb eucalyptus trees… planted here in the 1850s by way of Australian imports when the state needed cheap lumber; cowbirds fly our skies; there are literal jumping worms in our soil that self-reproduce and thrash about, consuming other fossorial invertebrates with abandon.

Suffice it to say, that much like the city’s residents, San Francisco is a place for misfits and transient sentient beings. However, one ecological oddity is raising alarms from biologists after a particular big ol’ boi was spotted in Golden Gate Park recently.

Sunset resident Bob Johansen was taking a casual stroll around Blue Heron Lake, previously known as “Stow Lake” until it was officially renamed last month, inside San Francisco’s Golden Gate Park when he stumbled upon a particularly gobsmacked sight: a vvv (vvv) big, springy amphibian.

“A new friend at Blue Heron Lake,” he wrote in a post on Nextdoor about two weeks ago. “Huge. At least eight inches long.”

“In my 15 years living in San Francisco and walking through Golden Gate Park and the Presidio,” he continued — “I have never seen a toad or a frog.”

(Mind you, the San Francisco Bay Area is home to numerous species of amphibians; it’s not unusual to see native Sierran tree frogs and Western toads in San Francisco, though you have to be pretty attentive to notice, as most either camouflage well into their habitats and spend much of their times in burrows and holding spots.)

The verdict is still undecided, but the picture uploaded to the hyperlocal community service app is an American bullfrog — an invasive now common throughout much of California, including the SF Bay Area. It’s unclear when the species of frog was introduced into San Francisco, but the first American Bullfrogs were first recorded in California sometime in the late 1890s or early 1900s, though accounts vary from sources.

Native to the Eastern and Southeastern United States, bullfrogs can be anywhere between two to four times the size of any native frog species, with males being larger than females; it’s their size why they were widely consumed as a food source in California, particularly with Chinese immigrants, as prepared frog legs were a common dish — with some records showing frogs’ legs were common sources of calories in southern China as early as the first century AD. Frog legs are usual fare in many Chinatown restaurants. The overwhelming number are made from American bullfrogs, though leopard frogs (a much smaller, less desirable frog for cuisine that’s native to North America)  are occasionally consumed.

Frog legs are best prepared from freshly killed animals, as amphibian meat is vastly different than mammalian and avian meat, which can be frozen and kept on ice without much damage to the meat’s quality and texture. The same can’t be said of amphibian meats, like frog legs.

Inevitably, some of these live frogs can escape from their shipping container, adding to the already established popularity of American bullfrogs in San Francisco, many of which were also later introduced as insect control. though as of December of 2023, the importation of American bullfrogs into California — and by proxy, into SF — was made illegal, making the American bullfrog the first illegal invasive amphibian in the state’s history.

According to the California Department of Fish and Game, bullfrogs are prolific throughout much of the state, as mentioned prior— “they’re literally everywhere,” said a representative of the California Fish and Game Commission to the San Francisco Chronicle.

But, per Deb Campbell, a spokesperson for the San Francisco Department of Animal Care and Control, no calls have ever come in about bullfrogs in Blue Heron Lake. This could make the frog Johansen spotted in the lake likely the first recording of an American bullfrog in that area… which is detrimental for many reasons.

Bullfrogs consume everything in sight, capable of eating small mammals, like mice, other amphibians, fish — even birds. They can drive other carnivores, of which all native frog species to San Franciso are meat-eaters, to extinction by way of starvation or in search of new areas to forage. They also have few natural predators, meaning their populations can explode being, more or less, unaffected by predation rates common with smaller frogs. They can also be asymptomatic carriers of chytrid — a lethal fungal disease that the overwhelming majority of amphibians don’t have a level of immunity against. 

They’re Godzillas. They can bring an entire freshwater ecosystem to its knees.

It’s unclear what impact bullfrogs have already had on San Francisco or what damage they could do in the future as their population inevitably grows, but it’s safe to say they likely won’t be named the SF’s official animal anytime soon. Or ever.

Feature image: Courtesy of Nextdoor via Bob Johansen

Matt Charnock