The San Francisco Garter Snake was once a prized pet. Collectors sought them out for their striking beauty and easy-going temperament. Their relationship with humans became a tale of going too far.
In pursuit of profits, humans harvested the snakes or drove them from their homes. Today, the species is under threat of extinction. Wildlife agencies spearheaded the preservation of the remaining populations. Their work helped San Francisco garters gain federal protection.
While genetically similar to garden snakes, this subspecies has evolved its quirks. Beyond their color, San Francisco garter snakes have developed unique ways of life.
Throughout this piece, you’ll learn how to identify the snake based on color and behavior. San Francisco garters exist under unusual circumstances. Find out how the snakes have evolved and how humans can help this at-risk snake rebound.
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The San Francisco garter snake bears the binomial name of Thamnophis sirtalis tetrataenia. It is one of America’s rarest and most beautiful snakes. They are a subspecies of the common garter snake but are not often mistaken for them.
Most garter snakes get called garden snakes. They are not different species, and the name connotes the same snake.
San Francisco garter snakes fall under the Colubridae family. This is the largest family of snakes in the world. The snake is one of 249 genera of Colubridae. Most species are non-venomous and inhabit every continent besides Antarctica.
After seeing a San Francisco garter snake, it’s easy to understand why they were once popular pets. The snake has bright, dramatic colors down its body. Their timid, curious nature made them easy to manage.
Visually, the bright red and teal markings down the body define the snake. The red lines contrast with multiple black ones down the body. Another key identifier for the species is the head. From above, the snake’s head will be rust red.
In the natural world, bright colors often signal a poisonous animal. The San Francisco garter does carry a small amount of venom in its saliva. Researchers believe the bright colors are not for displaying toxins.
Their coloring matches their habitat brilliantly and remains camouflaged along water banks. The blue-green underside allows the snake to stay hidden from prey below.
During the night, their belly will blend into the water’s surface.
San Francisco garters are one of the smallest garter snakes. Fully grown male snakes average around 39 inches (99 centimeters) in length. Females are longer and heavier and can reach up to 47 inches (199 centimeters). The heftier frame assists in carrying their young before hatching.
These snakes rely on their tongues to understand the environment around them. Odors and stimuli get processed to inform hunting, communication, and threats. This instinct helps their slim chances of reaching maturity.
If approached, the snake has three primary defenses. The first is scurrying up bushes or trees in hopes the predator cannot reach them.
If water is available, the snakes are adept swimmers. When being chased, San Francisco garters will look for a pond to escape.
When the San Francisco garter feels there is no escape, they release a foul-smelling odor. A powerful smell of rotten eggs will drive predators away. They leave convinced the meal is not worth the risk.
Geography and Distribution
San Francisco garter snakes have a limited distribution today. Despite their name, the snake lives in San Moreno County. All six sustained populations only inhabit various wetlands in the San Moreno area.
You can observe these snakes in the Pescadero Marsh Natural Preserve and the Ano Nuevo State Reserve. If visitors are lucky, places like these offer the rare chance to see this beautiful snake.
The San Francisco Zoo is one of the only zoos in the world with captive San Francisco garters. They offer people the rare chance to observe and learn about the snake up close.
The snakes love the thickly vegetated banks of ponds. Along the shorelines, the snakes look for rocks and thickets of weeds to hide.
Rocks also serve as sunning spots for the snake. Cold-blooded animals need to warm their bodies before they can actively hunt.
Their habitat is crucial to the survival of the snake. It needs rocks to hide and water to flee from its long list of predators. These spots also serve as ambush points for the snakes.
The snakes do not often move from their wetland homes. When winter begins, San Francisco Garters seek higher grounds and warmer temperatures. If the water gets too cold, the habitat is not as viable for these cold-blooded creatures.
San Francisco garter snakes prefer eating small vertebrates found in their wetland habitat. Frogs, toads, and insects are all options when cruising the shoreline. When the snake opts to swim, they hunt for small fish.
The snake uses its tongue to detect any new odors in the area. With decent vision, the snakes are capable of tracking and consuming prey.
Most snakes that inhabit wetlands will prey on newts. However, there is one species that only the San Francisco garter is capable of eating. The California Newt is a poisonous species of newt so toxic no other animal can eat them.
San Francisco snakes evolved a way to eat California newts. Their bodies began developing a resistance to the toxin over time.
The resistance made the newts fair game. It has started an evolutionary battle between the two species. Researchers documented cases where a population of newts was able to evolve a new toxin. The newts were again poisonous to the San Francisco garter. New toxins forced the snakes to change as well.
The back and forth has gone on for years. As new toxins develop, snakes adapt over time and can consume them once again. The two species remain locked in an evolutionary battle, changing as necessary to eat or be eaten.
Mating and Reproduction
The breeding season for the San Francisco garter snake is during the spring. During this time, females release pheromones to attract a mate.
The release triggers a frenzy among the surrounding male population. Snakes will race to get to the female first. If multiple arrive, the snakes intertwine. The wrestling and shoving form a ball, and the best fighter earns the right to breed.
The males do not stay long, and females are left to incubate the eggs by themselves. San Francisco garter snakes don’t lay eggs. Females store them internally until they hatch, making them an ovoviviparous species.
After two to three months, the female will give birth to live young. A typical hatch will yield 16 babies on average, and few will be lucky enough to reach maturity.
Baby snakes emerge 5 to 7 inches (12.7 to 17.8 centimeters) long and are ready to hunt immediately. It will take two years before the San Francisco garter snake babies reach maturity.
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Population & Conservation Status
Common garter snakes are one of the most common species found in North America. But this particular subspecies is the rarest. There are currently six significant populations remaining in the wild. Four of those populations have declined in recent years.
Consequently, only one to two thousand San Francisco garters remain in the wild today.
The snake became one of the first species protected by the Endangered Species Act in 1967. San Francisco Garter Snakes are still at risk of extinction. Continued efforts are necessary for the population to rebound.
By law, developing near the six current populations is prohibited. The act also outlaws owning, threatening, or forcing the snakes from their habitat.
The Endangered Species Act has a 99% success rate. It should only be a matter of time before they thrive.
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Threats and Predators
The primary threat to the snake has and continues to be humans. Developing roads and houses destroys their habitat and fragments populations. When this happens to such a delicate species, it’s unlikely they will survive.
As humans encroach on their habitat, they introduce more threats beyond habitat loss. Pesticides and overgrazing can kill the snakes if they do not relocate.
Beyond humans, these small snakes have a long list of predators. Herons, hawks, foxes, and bullfrogs are all capable of eating adult snakes. Post-hatch, the predator list grows to include smaller birds, snapping turtles, and squirrels.
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All garter snakes serve a vital role in managing rodent and insect populations. Their diet consists of multiple animals known for carrying bacteria or viruses. Consuming insects helps prevent diseases from spreading to different animals.
With so many natural predators, snakes also have a role as prey. More substantial birds and animals target the smaller snakes. If the population of garter snakes declines, theirs could suffer as well.
Healthy populations of the San Francisco garter snake are a sign of a healthy ecosystem. The snake is more sensitive to environmental shifts than most other species. If they are thriving, the environment around them likely is too.
Are San Francisco Garter Snake Dangerous?
San Francisco garter snakes pose no danger to humans. Their first instinct will always be to avoid confrontation with anyone. It’s unlikely most people ever encounter the snake.
This species does have the ability to produce venom in its saliva. While this can kill small prey, it does not threaten humans.
If someone is unlucky enough to get bitten, the bite will only cause mild irritation. If the wound gets cleaned within a few hours, it will heal in a couple of days.
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Representation in Mythology
There are no mentions of the San Francisco garter snake in Native American legend. The garter snake does have some representation in its lore.
The meaning of the snake varies from tribe to tribe. For some, the garter snake symbolizes jealousy or dishonesty. Others viewed them as a symbol of water.
Fun Facts about San Francisco Garter Snakes
Can you own a San Francisco garter snake?
Many species of garter snakes make entertaining pets. Today, you cannot own a San Francisco Garter Snake. The species is considered endangered in the United States.
Federal laws prohibit the sale and purchase of these snakes. When agencies lobbied for the snake’s protection, they mentioned keeping them as pets. For years pet trade posed the largest threat to the snake population.
Why do garter snakes stink?
Garter snakes are a smaller species and have a long list of predators. Danger lurks each time a garter is in the open, and their foul-smelling musk is their best defense.
The musk is released via its cloaca (anus) and is a similar defense system to the skunk. When the garter snake perceives danger, they spray musk in the threat’s direction. The stench of rotten eggs is often foul enough to convince predators to leave.
Can garter snakes climb walls?
Garter snakes will flee up small trees and bushes if threatened, but it’s unlikely they can climb a wall. If a surface lacks any structure to hold, a garter snake will have to find another route. Their slight frames cannot reliably vault them up more than a couple of feet.