How Midpen is Partnering to Save an Endangered Snake
Published September 4, 2025
The San Francisco garter snake can be found only in San Mateo County — and nowhere else on earth. These striking and elusive reptiles are severely threatened by many factors, including habitat loss and fragmentation, drought, disease, vehicle strikes, declining prey populations, low genetic diversity, competition from and predation by invasive species and illegal poaching.
These threats are nothing new. In fact, the San Francisco garter snake was first listed as endangered in 1967 on the U.S. Fish and Wildlife Service’s very first endangered species list. Yet, despite decades of special protection, the snake’s survival remains precarious.
To thrive, the snakes require a specific and diverse blend of habitats: large, intact coastal grasslands and a mosaic of year-round ponds and seasonal wetlands. Just as importantly, this exceptional endemic species needs a diverse coalition of partners working together toward its recovery.
That’s why Midpen has joined forces with the National Park Service’s Golden Gate National Recreation Area, San Franciso Recreation and Parks Department, U.S. Geological Survey and San Francisco Zoo to collaboratively develop a population enhancement plan.
In the spring of 2025, project partners collected 11 pregnant female snakes from a population on the San Mateo County coast. These snakes were transported to the San Francisco Zoo where they are currently under special care. Unlike many other snake species, garter snakes don’t lay eggs. Instead, their eggs develop internally, and the snakes give birth to live young. These mothers are expected to give birth in late summer or early fall 2025 and will be returned home once their offspring are born.
The project team is hopeful for a strong outcome, with early ultrasounds showing that the goal of 80-120 live snakes being born is feasible. Once the young snakes have grown large enough to survive in the wild, one third will be released to the site where the mother snakes were originally collected.
The remaining two-thirds will be released at other known San Francisco garter snake population sites in dire need of additional snakes to diversify and bolster the gene pool. Each baby snake will be genetically tested to ensure that there is a good mix of genes going to each population.
While many open spaces theoretically offer the right conditions for San Francisco garter snakes, only a handful of confirmed populations exist — many of which are genetically isolated, with dwindling numbers. For the species to be removed from the endangered species list, there must be at least 10 viable, self-sustaining breeding populations, each with over 200 individuals.
“The need to protect and support the San Francisco garter snake was recognized before the Endangered Species Act even existed, and fortunately, it is not too late for them,” said Midpen biologist Ariel Starr. “Our extensive efforts will help ensure that the people of the Bay Area will have a chance to admire this snake for generations to come.”
Through continued collaboration, habitat restoration, and science-driven actions like this head-starting program, Midpen and our partners are giving the San Francisco garter snake a fighting chance. The clock is ticking — but with a shared vision and forward-looking action, there’s hope for a comeback.