When I was a kid, I was an amateur herpetologist.
By Kurtis Alexander, Staff Writer Sep 11, 2025
The San Francisco garter snake, with its brilliant hues of deep red and turquoise, is widely considered one of the most beautiful snakes in North America. It’s also one of the rarest, with maybe 2,000 living in the wild today, all in San Mateo County.
In a bid to ensure a future for the endangered snake, Bay Area scientists are teaming up on a first-ever effort to rear a captive colony of the colorful crawlers, with plans to start releasing the newborns and rebuilding their populations at local ponds and hillsides.
“If we don’t have more snakes out there, they could disappear in our lifetime,” said Rochelle Stiles, director of field conservation for the San Francisco Zoo and Gardens, where the captive group is being raised. “The snakes serve a very important role in the ecosystem.”
This Bay Area snake is one of the nation’s most beautiful — and rare. Can scientists save it?
Greg
Quick and Dirty
The San Francisco garter snake, with its brilliant hues of deep red and turquoise, is widely considered one of the most beautiful snakes in North America. It’s also one of the rarest, with maybe 2,000 living in the wild today, all in San Mateo County.
In a bid to ensure a future for the endangered snake, Bay Area scientists are teaming up on a first-ever effort to rear a captive colony of the colorful crawlers, with plans to start releasing the newborns and rebuilding their populations at local ponds and hillsides.
“If we don’t have more snakes out there, they could disappear in our lifetime,” said Rochelle Stiles, director of field conservation for the San Francisco Zoo and Gardens, where the captive group is being raised. “The snakes serve a very important role in the ecosystem.”
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The effort to keep the San Francisco garter snake from sliding into extinction involves an array of federal, state and local entities, including the U.S Geological Survey, National Park Service, Golden Gate National Parks Conservancy and Midpeninsula Regional Open Space District.
On a recent morning, Stiles and her colleague Jamie McNellis, a conservation specialist, entered a locked room on the quarantined, animal-rearing grounds of the San Francisco Zoo, where the two are playing their part in the repopulation project by overseeing snake reproduction.
Ten mother snakes, which had been trapped in the wild while pregnant and then driven to the zoo, rested in small, heated enclosures, having recently given birth to a total of 117 baby snakes. A single female can produce up to 30 young in a litter.
According to Stiles, just 1% of snakes in the wild survive to adulthood while those raised at the zoo will see a 98% survival rate. The pregnant females also come to term more quickly in captivity.
A female adult San Francisco garter snake that was used for breeding is pictured at the San Francisco Zoo on Sept. 4.
Gabrielle Lurie/S.F. Chronicle
“All of the moms are eating, which is the biggest indication of them being comfortable,” said McNellis, after fetching the largest of the garter snakes from its bin and letting it slither in and out of her hands. “She’s a very big girl. She’s also the most social.”
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The big snake, known as #308, is nearly double the size of the others, measuring more than 4 feet long and about three-quarters of a pound, enjoying the zoo diet of earthworms, mice and fish.
Outside of captivity, San Francisco garter snakes have not been as successful.
The snakes have historically lived in wetlands and grasslands only on the San Francisco Peninsula: in San Mateo County and northern Santa Cruz County. (They’ve never resided in their namesake city.) Much of their limited habitat has been developed for housing and farming while invasive predators, such as bullfrogs, have proliferated, all squeezing out the native reptile.
Also, the striking appearance of the snakes once made them a premium target of the illegal pet trade. The snakes are characterized by a wide, blueish dorsal stripe that stands in contrast to jet-black and reddish-orange stripes and a blue-greenish underbelly.
Their vivid coloring, unusual for North American snakes, is likely a defense mechanism, signaling to predators – falsely – that they’re venomous or poisonous. The San Francisco garter snake, like the many other types of garter snakes, is not a danger to people or pets.
The snake was listed as a federally endangered in 1967, setting the stage for protections that have fallen short of securing its recovery.
A short walk from where the mother snakes were held at the zoo stood another building that housed their babies.
The weeks-old snakes were not much longer than a pencil, and just as thin. They were spread across 28 bins, three to five per enclosure, each equipped with a water dish, moss and a log. They were being fed chopped-up worms.
Conservation specialist Jamie McNellis holds baby garter snakes at the San Francisco Zoo on Sept. 4. A group of researchers is raising a population of the endangered snakes with the intent of reintroducing them to the wild.
Gabrielle Lurie/S.F. Chronicle
Once the young snakes are about a foot long, possibly in a year, they will be released at two of the few remaining sites in San Mateo County where the animals have been documented, Stiles said. The areas, which the scientists don’t want to widely publicize in order to better protect them, include federal lands managed by the Golden Gate National Recreation Area.
The park service, Golden Gate National Parks Conservancy and others have spent decades working to improve garter snake habitat, initially in hopes of helping the existing population rebound but more recently in preparation for the reintroduced snakes.
Their work has included constructing ponds where small frogs and other favorite foods of the snakes reside; restoring grasslands and coastal scrub; and making sure people don’t accidently trample the reptiles.
“You see the use of boardwalks,” said Claire Mooney, vice president of park projects and conservation with the parks conservancy. “Snakes can now safely stay on their path of travel and migrate from pond to pond.”
At the same time, the San Francisco Zoo has been working to perfect its techniques for caring for the endangered crawler since the 1990s. The zoo is the only place where the animal is housed for protection. The snake is not currently on public display.
Those partnering on the project expect that the repopulation effort will continue for at least another year, and perhaps longer, contingent on funding.
This week, with the first round of mother snakes healthy and their babies steadily growing toward a size that makes them safe to release, nine of the 10 donor females were returned to their homes in southwestern San Mateo County. One remained on hand for observation.
A San Francisco garter snake is returned to its home in southwestern San Mateo County on Monday. The adult female had been captured to help rear a captive population of snakes at the San Francisco Zoo.
Marisa Ishimatsu
“We tried to release them at the exact points we caught them,” said Elliot Schoenig, biologist with the U.S. Geological Survey’s Western Ecological Research Center. “For the most part, they just cruised back in. Some skirted the edges of the pond, which is their typical foraging behavior. Hopefully, they’ll encounter a frog and settle back in.”
The mother snakes, which Schoenig and his team mostly caught by hand, were selected from areas with relatively high numbers of snakes and strong genetic diversity, to ensure the offspring would be robust.
Schoenig’s team has been monitoring the San Francisco garter snake population for two decades, helping arrive at the conclusion that the intervention effort is crucial.
Partners in the repopulation project underscore the importance of the snakes to both their local predators and prey and for helping bring balance to the Bay Area’s natural systems. They also say it’s special to have such a beautiful snake living in the region.
“As we go into the future, we’re probably going to have to maintain some artificial immigration and emigration,” Schoenig said. “I think this is going to be a really important tactic for protection of the snakes.”