San Francisco Garter Snake
Thamnophis sirtalis tetrataenia
Family
Genus
Species
Subspecies
Colubridae
Thamnophis
sirtalis
tetrataenia
Geographic Range
Western portion of San Francisco peninsula, along hillsides
from San Francisco city line south to Crystal Springs Reservoir
and along the coast to Año Nuevo State Nature Reserve.
Habitat
Dense vegetation bordering ponds and wetlands with nearby
open hillsides
Niche
Terrestrial, semi-aquatic, diurnal, carnivorous
Wild Diet
Frogs, toads, newts, small fish
Life Span
Unknown in the wild, 8 – 15 in captivity
Appearance
Body is black with turquoise and red stripes. Weight is between 120 – 190 grams, length is
18 – 51 inches, males are generally half as heavy as females.
Adaptations
Female San Francisco garter snakes release pheromones to attract mates. They mate in the
spring or fall and females give birth to live young with an average of 16 offspring. These babies are
5 – 7 inches long when born and will mature at two years of age. During dry summer months,
when prey is hard to find, San Francisco garter snakes will sometimes aestivate in rodent burrows.
When threatened, San Francisco garter snakes will escape into the water or try and defend
themselves by releasing a powerful musk with their feces, this makes them smell and taste bad.
Fun Facts
The San Francisco garter snake was one of the first species to be listed as endangered after
the Endangered Species Act was passed. These non-venomous snakes will grab their prey and
swallow it whole. They are one of the few animals able to eat the toxic California newt. The
San Francisco Zoo is one of the only zoos in the country with San Francisco garter snakes.
At the Zoo
Our San Francisco garter snakes live in the Koret Animal Resource Center.
Comparison
San Francisco garter snakes have similar defense mechanisms to other kinds of snakes. When
threatened, a snake will first try and escape. Depending on the type of snake this could be up
a tree, under a rock, into a burrow or in the case of the San Francisco garter snake, into the
water. If unable to escape, snakes will then resort to ‘bluffing’ such as a rattlesnake rattling or a
cobra raising its hood. Lastly, they will try to retaliate; venomous snakes might strike and nonvenomous snakes such as the San Francisco garter snake will emit a foul-smelling substance so
that their attacker will release them.
Status and Conservation
Endangered
Threats
Habitat loss and fragmentation, preyed upon by introduced species, pet trade, decline of food
sources, specifically the endangered California red-legged frog
Bibliography
Nature Trail Handbook, Animal Diversity Web, Woodland Park Zoo website
To see color photos of this animal, go to www.sfzoo.org/wildaboutartandscience
Snakes – Amazing Adaptations
Meets 3rd Grade California Science Content Standards – 3a and 3c (see Standards Key)
California Visual Art Standard 2.3 - Paint or draw a landscape, seascape, or cityscape that shows the illusion of
space.
Taking It Further - California Visual Art Standard 2.2 - Mix and apply tempera paints to create tints, shades,
and neutral colors.
Animal to Draw for Art Contest – A snake
Writing prompt for the sentence of the back of the student’s drawing – Describe one amazing
adaptation your snake has and how that adaptation helps it to survive.
Objective – To learn some of the amazing adaptations that have allowed snakes to thrive for millions
of years.
Time – 20-30 min
Background – Snakes most basic adaptation is the shape of its body. Their lack of arms and legs allows
them to get into small areas that other predators can’t get into. They have evolved many other
adaptations (some listed below) that have allowed them flourish.
Vocabulary –
Adaptation – a modification of an animal or plant that makes it more fit to live in its habitat.
Jacobson’s Organ – the two small pits on the roof of a snake’s mouth that assist with their sense of
smell.
Quadrate Bone – the bone that connects a snake’s lower jaw to the skull, it acts as a double-jointed
hinge to allow the mouth to open extra wide to swallow prey.
List of Adaptations Can enter narrow holes made by rodents
Can slither through grass or among rocks without causing a disturbance
Unusually flexible jaw with the quadrate bone, enabling them to swallow large prey
Snakes come in an incredible variety of colors and patterns, some for camouflage to avoid
detection and some are very bright as a warning to other animals
Rattlesnakes have rattles on their tail that can be shaken to make a very loud warning sound
Common garter snakes are equipped with glands that exude a very smelly substance when
the
snake is disturbed
King snakes have a tolerance towards rattlesnake venom which enables them to kill and eat
rattlesnakes
Rat snakes can climb up tree trunks
Gopher snakes can imitate rattlesnakes by flattening their heads and shaking their tail in dry leaves
Backward facing teeth to keep food moving in the right direction
Forked tongue to deposit scent molecules into a special section of the nasal cavity called the
Jacobson’s organ, where the odor is sensed
Materials – images of many different snakes showing: camouflage, tongue, rattle, etc.
Directions –
1. Break the class up into small groups of 3-5 students.
2. Review the many snake adaptations that have been discussed.
3. Explain to the groups that they will be designing their very own snake. Ask guiding
questions, such as: Will it be large and slow or small and fast? Will it be camouflaged so it
can’t be seen, or will it have bright colors to warn would-be predators?
4. In their groups, the students will work together to determine what their snake will look like,
what it eats and then draw a sketch of it. Each student should suggest at lease one
characteristic for the group’s snake. Have each group present their snake to the rest of the
class and show their sketch.
Questions for discussion – How does a snake’s lack of arms and legs actually help it to survive? How
does a snake’s forked tongue help it to smell?
Website/books/other resources – A Snake Mistake by Harriet Ziefert and Mavis Smith
Snakes: Biggest! Littlest! by Sandra Markle
The Snake Who Was Afraid of People by Barry Louis Polisar and David Clark
http://montereybay.com/creagrus/CAsnakeSFGarter.html
http://www.californiaherps.com/snakes/pages/t.s.tetrataenia.html
http://www.parksconservancy.org/our-work/park-stewardship/species/san-francisco-gartersnake.html
Current Event, San Francisco garter snakes relocated during construction http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2000/01/27/MN70501.DTL
Children’s Book – Vernon and the Snake by Crystal J. Stranaghan You can read this story from
Vernon’s perspective and then turn it over to hear the snake’s version of the story.
Taking it Further
Tongue Twisters
Sam saw a sneaky slimy snake in the sandbox.
The silly snake swam slowly in the stream.
Conservation Action – San Francisco garter snakes live near ponds and marshes where they have easy
access to their primary food source, red-legged frogs. Wetlands like these are disappearing due to
development and are sensitive to pollution. One great way to help take care of your local ponds and
marshes is to conserve water. Here are a couple of easy ways you can help:
 While waiting for hot water to run from your faucet, collect the cold water and use it
to water indoor and outdoor plants.
 Take shorter showers – challenge your family members to see who can take the
shortest shower and still get clean!
Source - http://www.backyardnature.net/snakadap.htm