San Francisco Garter Snake: Facts, Diet, Habitat and More

Have you ever seen a San Francisco Garter Snake? Those familiar with snake species in North America may recognize this, but don’t be fooled. The unique features and habits of the San Francisco Garter Snake make it stand out among other snakes!

The San Francisco Garter Snake, also known as Thamnophis sirtalis tetrataenia or the Red-sided Garter Snake, is a snake found predominantly in Northern California and parts of Oregon. It has an interesting history; first discovered by William Lucian Woodward in 1880, it was originally thought to be a subspecies of its sister Snake, Thamnophis sirtalis. However, further research determined that the two are separate species.

This article will provide information about the distinct features, habitats and behaviours of the San Francisco Garter Snake so that you can learn more about this unique creature and how to identify it if you encounter it in its natural habitat.

Characteristics / Physical Features

1. The eyes of the San Francisco Garter Snake are small and round.

2. Their head is triangular with a distinctive reverse-V marking at the top called a “supraocular” spot.

3. The scales on this species are keeled, giving them a rough texture.

4. They also have teeth that can be easily seen closely and anal plates that form a complete row between their ventral scales.

5. The San Francisco garter snake is a long slender snake which can be up to 24 – 48 inches long when fully grown (including head and tail).

6. Its body ranges from light grey or brown to dark grey or black, with three distinct yellow stripes along its back and sides.

7. The belly of the San Francisco Garter Snake is white with several darker spots.

Venomous Bite

The San Francisco garter snake is not venomous and does not have a dangerous bite. However, they possess sharp teeth, which can cause minor puncture wounds if handled roughly.

Be careful when handling these snakes, as their bites can become infected if not properly treated. If bitten, it is recommended to clean the wound with soap and water and apply an antibiotic ointmentor cream.


1. The San Francisco garter snakes tend to be quite active during the day, particularly during warm afternoons, where they can be seen basking on logs or rocks near water sources.

2. During cooler days, they would usually retreat in damp crevices and burrows located around wetland habitats such as ponds, marshes and streams, where it is more likely to capture prey like insects and frogs.

3. These fishes remain active throughout the fall into winter until temperatures become too cold to function normally.

4. They move deep into their winter caves in the colder months. During hibernation, they coil together there and then reappear in spring. Thanks to their adaptive colouring techniques, their colours are more vibrant at this time than before.

Habitat and Range

They inhabit various habitats, including coastal bluffs, deep canyons, moist redwood forests, meadows and marshes, open grasslands, and vernal pools. The variety of niche habitats used by this species reflects its incredible adaptability.


1. San Francisco garter snakes occupy a variety of habitat types within their range, including coastal bluffs and deep canyons along the coast, moist redwood forests in the hills, meadows and marshes in valleys and open grasslands around vernal pools.

2. They are also commonly encountered in urbanized areas like parks, yards, and gardens surrounding golf courses or similar sports facilities.

3. In addition to wetland environments such as ponds, creeks and streams, they also occupy inland riparian corridors.


The San Francisco garter snake is only known from northwestern California within a 60-mile radius of the base at San Francisco Bay.

The range includes San Mateo County on the northern extent to Sonoma County on the south, with some reports from Marin County bordering San Francisco Bay with reports from western Mendocino County to the east known too.

There is one reported occurrence just outside California’s border with Nevada. Two were found at an elevation of 6500 feet near Black Rock along Nevada Route 447, according to herpetologist Robert Fisher (Fisher et al., 1997).

Hibernation Sites:

San Francisco garter snakes prefer hibernacula that consist of underground caves, such as rock piles or mammal burrows. These sites’ temperatures remain relatively consistent throughout the hibernation period ranging between 41–45°F (5–7°C) during winter months (January-February).

To remain warm during chilly weather, they will congregate in large dens with up to hundreds of time-consuming resources stored over summer, such as rodent remains (Neher et al., 2011).

Diet and Feeding Habits

The San Francisco garter snake has an impressive array of prey items that it feeds on, but not much else is known about this reptile’s eating patterns or dietary needs to survive.

What Do San Francisco Garter Snakes Eat?

San Francisco garter snakes feed primarily on small fishes, minnows, fry, sticklebacks, and sculpins.

They have also been seen preying on amphibians like frogs, salamanders and newts; crustaceans such as crayfish; insects including beetles, grasshoppers and caterpillars; lizards; snails; small birds and mice.

It’s unknown whether these snakes’ diet changes seasonally or remains consistent throughout the year.

How Do They Find Their Food?

San Francisco garter snakes use their sense of smell to locate potential prey items before striking them with their bite. Once killed by a bite from this snake species, their food enters their mouth, where the prey item’s saliva quickly turns it into an easily digested liquid within their digestive tract for nutrient absorption.

Where Do They Find Their Food?

These creatures prefer near-shore habitats for hunting and can often be found near streams or other bodies of water where many smaller animals tend to congregate.

In addition to stream banks, San Francisco garter snakes often hunt in vegetable gardens for insects like caterpillars or beetles.


Reproduction in San Francisco garter snakes is typically seasonal, occurring between late March and early June. During this time, males will search for females to mate with and often travel long distances to find them.

Mating occurs in the water or on land near bodies of water. After mating, the female will lay her eggs in a moist environment, such as a rotting log or a pile of leaves.

The eggs will hatch after a few weeks, and the young snakes will be on their own from that point forward.

Predators and Prey

San Francisco garter snakes are preyed upon by various animals, including birds of prey, raccoons, skunks, foxes, coyotes, and other snakes. They have also been known to fall victim to larger fish in the water.

San Francisco garter snakes often hide in vegetation or caves to protect themselves from predators.

They also release a foul-smelling musk when threatened, which can help deter potential predators.

Conservation Status

The San Francisco garter snake is a species of special concern in California due to its limited range and declining population.

To protect this species, it is important to maintain healthy riparian habitats and reduce human disturbance in areas where the snakes are known to inhabit.

It is also important to reduce the amount of pollution entering waterways, as this can harm the health of the species.


Kingdom: Animalia

Phylum: Chordata

Class: Reptilia

Order: Squamata

Suborder: Serpentes

Family: Colubridae

Genus: Thamnophis

Species: Thamnophis sirtalis tetrataenia

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