Frog Invasion!

Keeping certain species out of Golden Gate Park is a decades-old battle.

In 2011, a massive effort launched to rid a small, quiet area of Golden Gate Park from a particularly nasty creature. Although invasive, South African clawed frogs are physically much less scary than they sound. Measuring only five inches long, with round heads, pincer-like front feet, and bulging eyes, they are thought to have first entered the U.S. in the 1940s, and have a voracious appetite for just about everything. They also carry the toxic fungus Batrachochytrium dendrobatidis, or Bd for short. In the early 2010s, more than 10,000 were estimated to be living in a small lily pond wedged between JFK and Nancy Pelosi drives, eating and infecting everything in sight.

“The clawed frogs will eat anything that moves in front of them,” Eric Larson, an environmental manager with the state’s Fish and Wildlife Department, told environmental publication Bay Nature in 2013. “There’s nothing else at the pond now because of them, no fish and no frogs. They’re voracious feeders, highly reproductive, and have no known predators.”

Eventually, it reached a point that no longer could be ignored, but eradicating them was no small feat. The pond couldn’t simply be drained out of fear the frogs would hop over to other areas of Golden Gate Park. Hand-catching and euthanizing them was time-consuming amid the overgrown duckweed; even with all hands on deck, researchers were still regularly trapping between 200 and 500 each week. The time it took to catch frogs and humanely put them down with carbon dioxide was exhausting, and they were breeding as fast as they were dying.

In the end, Fish and Wildlife resorted to chemicals. Seeing as there were almost no other species left in the lily pond by that time, they added low doses of chlorine to the water and covered it with yellow and blue tarps.

Runners who frequented the once-beautiful route were met with two years of fences and efforts to revitalize the area, before it finally reopened. But today, it’s back to a healthy ecosystem, with ducks, turtles, birds, and an absence of duckweed.

This isn’t the first time a battle has been waged to eradicate invasive species across the park. Feral hogs, which are evolved versions of the European wild boar, once roamed Golden Gate Park freely, digging up plants and preying on small animals. Today they can still be found in rural areas of Alameda County, but thanks to efforts from the National Park Service in the 1980s, have since been eradicated in San Francisco.

Harder to trap — though there’s no lack of effort in trying — are Norway rats and black rats, which are skilled climbers and can decimate entire nests full of eggs or baby birds. Walk by the Music Concourse at dusk on a weekend, and you can hear dozens of them scurrying around in trash cans lining the sidewalks, eating the remains of Twirl and Dip ice cream cones.

While much of the damage done in introducing invasive species to California occurred generations ago, officials have become wise as to what types of animals are regularly set free in city parks. A massive effort was made to clear Mountain Lake in the Presidio of invasive carp, goldfish, and other pets that had been released into the waters over the years. So tricky was a solution that the Presidio Trust ended up having to pump 47 gallons of poison into the lake, effectively killing everything inside. After the operation was concluded, they came up with a simple plan: Now, at the small sandy beach abutting Mountain Lake, a large wooden aquatic rescue box sits under a bush. “This box is checked daily,” a placard states, inviting anyone carrying a turtle, goldfish, frog, or plant to drop it inside. Lift up the lid, and a steep plastic slide ends in a few inches of water.

Thus far, no drop-off boxes have been installed in Golden Gate Park, but signs dot the perimeters of Stow Lake banning people from releasing their former pets into the wild. With a little social responsibility and the keen watch of biologists, the worst of the park’s animal invasions may be behind us. 

But don’t even get us started on the eucalyptus trees.

Read more from SF Weekly‘s Golden Gate Park issue:

Golden Gate Park: You Can Lead a Horticulture
A wilderness transformed into lungs for the 19th-century San Francisco.

Sharon Meadow Has Been Renamed Robin Williams Meadow
Comics and goodnatured city dignitaries gathered in Golden Gate Park on Friday to mutilate some Robin Williams jokes in honor of the late comedian.

Golden Gate Dog Park Renovation Will Separate Large Dogs From Small
How do we break it to dogs that the $2.4 million upgrade to their park-within-a-park isn’t coming for another year?

Volunteering at the National AIDS Memorial Grove
Redwoods are inherently contemplative, bringing new perspective on an epidemic that is passing into history.

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