San Francisco Garter Snake

Thamnophis sirtalis tetrataenia

Last updated: May 18, 2022
Verified by: AZ Animals Staff
Image Credit reptiles4all/Shutterstock.com

The San Francisco garter snake is among the rarest snake species in the United States.

San Francisco Garter Snake Scientific Classification

Kingdom
Animalia
Phylum
Chordata
Class
Reptilia
Order
Squamata
Family
Colubridae
Genus
Thamnophis
Scientific Name
Thamnophis sirtalis tetrataenia

Read our Complete Guide to Classification of Animals.

San Francisco Garter Snake Conservation Status

San Francisco Garter Snake Locations

San Francisco Garter Snake Locations

San Francisco Garter Snake Facts

Prey
Frogs, fish, birds, reptiles, and small mammals
Fun Fact
The San Francisco garter snake is among the rarest snake species in the United States.
Litter Size
10-40 live young
Diet
Carnivore
Common Name
San Francisco garter snake

San Francisco Garter Snake Physical Characteristics

Color
  • Red
  • Black
  • Green
Skin Type
Scales
Lifespan
6-14 years
Length
18-55 inches
Venomous
Yes
Aggression
Low

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View all of the San Francisco Garter Snake images!



The San Francisco garter snake is among the rarest snake species in the United States.

The San Francisco garter snake is a subspecies of the common garter snake. Swathed in bright, flamboyant colors, it is also among the most unique-looking species. While almost completely harmless to humans, they are surprisingly effective and deadly predators against smaller animals. This article will cover some interesting facts about the appearance, behavior, lifespan, and location of the San Francisco garter snake.

5 San Francisco Garter Snake Amazing Facts

  • The reproductive season of the San Francisco garter snake takes place in the spring and perhaps even the fall. The females produce anywhere between 10 and 40 young per clutch each year. Instead of eggs, she gives birth to live young, which begins to hunt almost immediately. The lifespan is thought to reach a maximum of about 14 years.
  • The San Francisco garter snake is mostly active during the day. They are considered to be excellent swimmers and also move quickly on the ground.
  • One of the most interesting facts is that the San Francisco garter snake is immune to the dangerous toxins of the Pacific newt. In fact, a kind of evolutionary arms race has developed between the two species. The toxicity of the newt and the resistance of the snake both tend to vary together by location.
  • Hawks and herons appear to be the main predator of the San Francisco garter snake.
  • Like other types of snakes, the San Francisco garter snake has the ability to sense smell with an organ located on the roof of its mouth. When it flicks out its tongue, the snake is gathering odor molecules from the air.

Where to Find San Francisco Garter Snakes

The San Francisco garter snake is found exclusively around the San Francisco Peninsula area of California. They prefer to inhabit grasslands or wetlands near ponds and marshes. It is possibly the rarest and most difficult to find of all the subspecies of the common garter snake. The closest related subspecies geographically is the California red-sided garter snake.

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San Francisco Garter Snake Scientific Name

The scientific name of the San Francisco garter snake is Thamnophis sirtalis tetrataenia. Thamnophis essentially means bush or shrub snake in Greek. Sirtalis is thought to derive from the Latin word for a garter. Tetrataenia means four ribbons, a reference to the number of stripes on its body.

San Francisco Garter Snake Population & Conservation Status

Although the common garter snake as a species is classified as least concern by the IUCN Red List, the San Francisco garter snake subspecies have not been given a specific classification by that organization. However, it is considered to be an endangered species by the US government, and as a result, it is protected by the US Endangered Species Act. Some of the greatest threats posed include poaching, accidents, and habitat loss from commercial and urban development. Exact numbers are not available, but the remaining populations are thought to be heavily fragmented from each other. An isolated population of 1,300 was found to reside near the San Francisco international airport.

How to Identify the San Francisco Garter Snake: Appearance and Description

The San Francisco garter snake has one of the most unique patterns of any snake in the world. It is characterized by bright blue-green or green-yellow coloration along the stomach and sides, plus another green stripe running along the entire length of the upper back. This is surrounded on both sides by two black stripes and a deep red stripe in between. The upper half of the head is colored red and orange, whereas the lower jaw and cheeks are colored bluish-green. The average length is about 3 feet long, but they can sometimes reach a length of more than 4 feet as well.



Here is how to identify the San Francisco garter snake:

  • Small, slender body measuring an average of 3 feet
  • Alternating stripes of green, black, and red
  • Large round eyes in comparison to body size
  • The head is slightly larger than the neck
  • Prominent keeled scales on the back

San Francisco Garter Snake Pictures

The San Francisco Garter Snake characterized by bright blue-green or green-yellow coloration along the stomach and sides.
The San Francisco Garter Snake is characterized by bright blue-green or green-yellow coloration along the stomach and sides.

reptiles4all/Shutterstock.com

San Francisco garter snakes, endemic of California, have small, slender bodies measuring an average of 3 feet.
San Francisco garter snakes, endemic to California, have small, slender bodies measuring an average of 3 feet.

spatuletail/Shutterstock.com

The upper half of the head of the San Francisco garter snake is colored red and orange, whereas the lower jaw and cheeks are colored bluish green.
The upper half of the head of the San Francisco garter snake is colored red and orange, whereas the lower jaw and cheeks are colored bluish-green.

Yurkovski/Shutterstock.com

San Francisco Garter Snake: How Dangerous Are They?

The San Francisco garter snake is completely harmless to humans. Although they do have the ability to produce venom in their saliva that kills their prey, this snake does not actually have any fangs to deliver the venom deep into the body. The venom will cause nothing more than mild irritation to the human skin. It does not require any medical attention unless symptoms happen to persist for a long time.

San Francisco Garter Snake Behavior and Humans

The San Francisco garter snake is very timid and wary around humans. When threatened, their first instinct is to run away and hide, usually straight into the water. If mishandled, this snake may release a foul-smelling odor and attempt to bite its assailant. While they pose no danger to people, they should be left alone. Because they prefer to live in wetland habitats, they are rarely seen and difficult to catch.

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San Francisco Garter Snake FAQs (Frequently Asked Questions) 

Are San Francisco garter snakes venomous?

This snake’s saliva is considered to be mildly toxic, but it causes nothing more than minor skin irritation to humans.

How do San Francisco garter snakes hunt?

The San Francisco garter snake locates prey with its excellent sense of smell and decent sight. It will strike quickly and bite its prey. The venom in the saliva is often fatal to smaller animals.

Are San Francisco garter snakes aggressive?

The San Francisco garter snake is not considered to be aggressive around humans.

Where do San Francisco garter snakes live?

The San Francisco garter snake lives exclusively around the San Francisco Peninsula in California.

What do San Francisco garter snakes eat?

The San Francisco garter snake has a large and varied diet consisting of frogs, newts, fish, birds, worms, reptiles, and more. One of its favorite meals is the equally endangered red-legged frog.

Can you own a San Francisco garter snake?

The San Francisco garter snake is protected by the US Endangered Species Act, and therefore it is illegal to own one in the United States at any price. Some people still poach them and smuggle them out of the country, where they can easily go for a price of more than a thousand dollars. This exorbitant price is due to their rarity.

Why is the San Francisco garter snake endangered?

Even before San Francisco became a major city, this species already had a small, restricted range that didn’t really overlap with the surrounding subspecies. It then had the misfortune of losing much of its remaining land to urban and commercial development as well as agriculture. Poaching, pesticide use, and road accidents also proved to be significant factors in its decline.

Are San Francisco garter snakes only found in San Francisco?

Yes, they are only found in San Francisco and the immediate surrounding locations.

Thank you for reading! Have some feedback for us? Contact the AZ Animals editorial team.

Sources
  1. California Herps, Available here: http://www.californiaherps.com/snakes/pages/t.s.tetrataenia.html
  2. The Guardian, Available here: https://www.theguardian.com/us-news/2021/aug/19/san-francisco-airport-endangered-garter-snake

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