Geographic Range
Plains garter snakes are found throughout the North American plains region, from the
Oklahoma panhandle, northernmost Texas, and northeastern New Mexico north to southern
Alberta, Saskatchewan, and Manitoba, and east through Minnesota, Wisconsin, and Indiana.
Habitat
Plains garter snakes are found in meadows, prairies, and other grasslands near sources
of water, such as ponds, streams, marshes, and sloughs. They may also be found in
swampy areas or along rivers. They may be found in suburban or urban vacant lots.
Habitats they occupy may be influenced by the presence of a congener; where they co-occur
with common garter snakes (
Thamnophis sirtalis
), they may be found in more dry habitats than common garter snakes.
- Habitat Regions
- temperate
- terrestrial
- Terrestrial Biomes
- savanna or grassland
Physical Description
Plains garter snakes are long, striped garter snakes, usually from 40 to 70 cm long,
but occasionally up to 109.5 cm. They have a dorsal and two lateral, yellow or orange
stripes on a background scale color of dark brown to dark greenish. Lateral stripes
are on scale rows 3 and 4. The sides may have some red pigmentation. Scales are keeled
and measure 19 to 21 rows at the mid-body. There is a row of black spots between the
lateral stripes and the ventral scales. They have an undivided anal plate. Males are
slightly larger, with more ventral and subcaudal scales and slightly longer tails.
Male tails are about 20.5 to 27.8% of total body length, whereas females have tails
that are 17.6 to 27.5% of their body length. Males also have tubercles on their chin
shields. There are no described subspecies.
- Other Physical Features
- heterothermic
- Sexual Dimorphism
- male larger
- sexes shaped differently
Development
Plains garter snakes grow at a rate of approximately 1.1 cm per week during their
first year. Growth rates slow in subsequent years.
Reproduction
Males track females via pheromone trails and compete for mating opportunities with
receptive females. Males crawl alongside females and push on her with their noses
while their bodies undulate. They touch the female's back with their tongues and attempt
to copulate. If the female is receptive, she will raise her tail and allow copulation.
A seminal plug may be inserted to deter copulation with another male. Both males and
females can mate with multiple individuals.
- Mating System
- polygynandrous (promiscuous)
Mating takes place after these snakes emerge from hibernation, in April or May. Females
are sexually mature in their 2nd or 3rd year. Plains garter snakes give birth to live
young from June through September, after a gestation period of 83 to 102 days. There
are from 5 to 60 young in a litter, but usually 10 to 20. Litters may be larger in
northern parts of the range, litter size varies with nutritional status and size of
the female. Young are born at sizes from 11.9 to 24.1 cm and 0.93 to 2.48 g.
- Key Reproductive Features
- iteroparous
- seasonal breeding
- sexual
- viviparous
Females gestate and give birth to live young, investing significant nutritional resources.
After the young are born, there is no further parental involvement.
- Parental Investment
-
pre-fertilization
- provisioning
-
protecting
- female
-
pre-hatching/birth
-
provisioning
- female
-
protecting
- female
-
provisioning
Lifespan/Longevity
A captive plains garter snake was recorded living to almost 8 1/2 years.
Behavior
Plains garter snakes are active from March to November, depending on the region. They
may be active for shorter periods in northern portions of their range. They hibernate
in burrows or rock crevices, although they may emerge on warm, winter days. They often
hibernate in rodent burrows or ant mounts, but have also been found in crayfish burrows,
under sidewalks, in other man made crevices, and even underwater. Activity patterns
depend on air temperatures. They are active during the day at warm temperatures, usually
between 21 and 29 degrees Celsius. Once the air temperature goes above 31 degrees
Celsius, these garter snakes switch their active period to night. At much lower temperatures,
prairie garter snakes become inactive. Where they co-occur with common garter snakes
(
Thamnophis sirtalis
), plains garter snakes generally have higher body temperatures under the same conditions.
Daily activity patterns are also influenced by breeding condition, males spend more
time active during mating season and females spend more time active when they are
pregnant. These snakes are solitary outside of brief interactions with mates and grouping
during hibernation. There is some evidence that they can recognize individuals and
form dominance relationships.
- Key Behaviors
- terricolous
- diurnal
- nocturnal
- crepuscular
- sedentary
- hibernation
- solitary
- dominance hierarchies
Home Range
Plains garter snakes stay within relatively small home ranges for long periods of
time, moving only up to 76 meters over periods of over a year. They are not reported
to be territorial. Individuals released at distances from their area of capture were
able to return to their home range over relatively long distances. Population densities
have been estimated at between 69 to 123 per hectare.
Communication and Perception
Plains garter snakes use their sense of smell extensively. They find prey, mates,
and hibernacula by following chemical trails. They also use vision and vibrations
to detect threats and navigate. Some evidence suggests they may navigate using polarized
light. Males use touch in courtship rituals.
- Perception Channels
- visual
- polarized light
- tactile
- vibrations
- chemical
Food Habits
Plains garter snakes eat a wide variety of animal prey, overlapping significantly
with the prey preferences of common garter snakes (
Thamnophis sirtalis
). They have been recorded preying on frogs and toads, salamanders, fish, birds, small
rodents, leeches, earthworms, and grasshoppers. Amphibians eaten include northern
cricket frogs (
Acris crepitans
), American toads (
Bufo americanus
), great plains toads (
Bufo cognatus
), tree frogs (
Hyla
species), striped chorus frogs (
Pseudacris triseriata
), plains leopard frogs (
Rana blairi
), northern leopard frogs (
Rana pipiens
), and various salamanders. They have been recorded eating mosquitofish (
Gambusia affinis
), southern redbelly dace (
Phoxinus erythrogaster
), bluntnose minnows (
Pimephales notatus
), bank swallows (
Riparia riparia
), and eastern meadowlarks (
Sturnella magna
). Plains garter snakes find prey by following an olfactory trail, then grabbing prey
once they catch up with them.
- Animal Foods
- birds
- mammals
- amphibians
- fish
- insects
- terrestrial worms
Predation
Plains garter snakes may be preyed on by birds of prey, such as red-shouldered hawks
(
Buteo lineatus
), Swainson's hawks (
Buteo swainsoni
), kestrels (
Falco sparverius
), and northern harriers (
Circus cyaneus
). Other predators include foxes (
Vulpes
), coyotes (
Canis latrans
), striped skunks (
Mephitis mephitis
), mink (
Neovison vison
), domestic cats (
Felis catus
), and milk snakes (
Lampropeltis triangulum
). Humans also incidentally and intentionally kill prairie garter snakes. These garter
snakes will bite, emit a foul smelling musk, or defecate to discourage predators.
Their lateral stripes make them difficult to see in their grassy habitats and as they
move. Plains garter snakes also have a series of antipredator displays that they will
use, including hiding their heads, striking with the mouth closed or open, coiling
or balling up their bodies, extending the body flat on the substrate, and waving the
tail. They might also take refuge in water. Responses to threats vary with age.
- Anti-predator Adaptations
- cryptic
Ecosystem Roles
Plains garter snakes are important predators of amphibians, earthworms, leeches, and
other animals in their prairie habitats.
Economic Importance for Humans: Positive
Plains garter snakes are important members of the native prairie habitats they are found in.
Economic Importance for Humans: Negative
There are no adverse effects of plains garter snakes on humans. These are nonvenomous
snakes that are shy and retiring, in general, although they will bite if threatened.
Conservation Status
Plains garter snakes are not considered threatened, although regional populations
may be vulnerable. They are considered endangered in Ohio and a species of concern
in Arkansas.
Other Comments
Genetic evidence suggests that
T. radix
is most closely related to
Thamnophis butleri
and
Thamnophis brachystoma
, among
Thamnophis
species.
Thamnophis radix
fossils are known from the Pliocene of Nebraska.
Additional Links
Contributors
George Hammond (editor), Animal Diversity Web Staff.
Tanya Dewey (author), University of Michigan-Ann Arbor.
- Nearctic
-
living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.
- native range
-
the area in which the animal is naturally found, the region in which it is endemic.
- temperate
-
that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).
- terrestrial
-
Living on the ground.
- tropical savanna and grassland
-
A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are found in parts of subtropical and tropical Africa and South America, and in Australia.
- savanna
-
A grassland with scattered trees or scattered clumps of trees, a type of community intermediate between grassland and forest. See also Tropical savanna and grassland biome.
- temperate grassland
-
A terrestrial biome found in temperate latitudes (>23.5° N or S latitude). Vegetation is made up mostly of grasses, the height and species diversity of which depend largely on the amount of moisture available. Fire and grazing are important in the long-term maintenance of grasslands.
- urban
-
living in cities and large towns, landscapes dominated by human structures and activity.
- suburban
-
living in residential areas on the outskirts of large cities or towns.
- riparian
-
Referring to something living or located adjacent to a waterbody (usually, but not always, a river or stream).
- heterothermic
-
having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.
- polygynandrous
-
the kind of polygamy in which a female pairs with several males, each of which also pairs with several different females.
- iteroparous
-
offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).
- seasonal breeding
-
breeding is confined to a particular season
- sexual
-
reproduction that includes combining the genetic contribution of two individuals, a male and a female
- viviparous
-
reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.
- diurnal
-
- active during the day, 2. lasting for one day.
- nocturnal
-
active during the night
- crepuscular
-
active at dawn and dusk
- sedentary
-
remains in the same area
- hibernation
-
the state that some animals enter during winter in which normal physiological processes are significantly reduced, thus lowering the animal's energy requirements. The act or condition of passing winter in a torpid or resting state, typically involving the abandonment of homoiothermy in mammals.
- solitary
-
lives alone
- dominance hierarchies
-
ranking system or pecking order among members of a long-term social group, where dominance status affects access to resources or mates
- tactile
-
uses touch to communicate
- chemical
-
uses smells or other chemicals to communicate
- visual
-
uses sight to communicate
- polarized light
-
light waves that are oriented in particular direction. For example, light reflected off of water has waves vibrating horizontally. Some animals, such as bees, can detect which way light is polarized and use that information. People cannot, unless they use special equipment.
- tactile
-
uses touch to communicate
- vibrations
-
movements of a hard surface that are produced by animals as signals to others
- chemical
-
uses smells or other chemicals to communicate
- cryptic
-
having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.
- carnivore
-
an animal that mainly eats meat
- piscivore
-
an animal that mainly eats fish
References
Ernst, C., E. Ernst. 2003. Snakes of the United States and Canada . Washington, D.C.: Smithsonian Books.
Harding, J. 2000. Amphibians and Reptiles of the Great Lakes Region . Ann Arbor, Michigan: University of Michigan Press.