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.

Biogeographic Regions: nearctic (Native )

This species ranges from central United States to south-central Canada. Its range extends from southern Alberta, Montana, eastern Wyoming, eastern Colorado and northeastern New Mexico eastward through southern Manitoba, Minnesota, southern Wisconsin and northern and central Illinois to northwestern Indiana and disjunctly to central Ohio, southward to northern Texas, western Oklahoma, and northern half of Missouri, at elevations of 120 to 2,290 m (400 to 7,500 feet) but usually below 1,830 m (6,000 feet) (Rossman et al. 1996, Hammerson 1999, Ernst and Ernst 2003, Stebbins 2003, Walley et al. 2003).

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.

Biogeographic Regions: nearctic (Native )

occurs (regularly, as a native taxon) in multiple nations

Canada

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

Global Range: (200,000 to >2,500,000 square km (about 80,000 to >1,000,000 square miles)) The range extends from southern Alberta, Montana, eastern Wyoming, eastern Colorado and northeastern New Mexico eastward through southern Manitoba, Minnesota, southern Wisconsin and northern and central Illinois to northwestern Indiana and disjunctly to central Ohio, southward to northern Texas, western Oklahoma, and northern half of Missouri, at elevations of 120-2,290 meters (400-7,500 feet) but usually below 1,830 meters (6,000 feet) (Rossman et al. 1996, Hammerson 1999, Ernst and Ernst 2003, Stebbins 2003, Walley et al. 2003).

Continent: North-America
Distribution: S Canada (Manitoba, Alberta, Saskatchewan), USA (Montana, North Dakota, South Dakota, Nebraska, Kansas, E Wyoming, E Colorado, NE New Mexico, Oklahoma, N Texas, Minnesota, Iowa, Wisconsin, Missouri, Illinois, Indiana, Arkansas)

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 widest part of the body. There is a row of black spots between the lateral stripes and the scales on their belly. Males are slightly larger, with slightly longer tails.

Range length: 109.5 (high) cm.

Other Physical Features: ectothermic ; heterothermic ; bilateral symmetry

Sexual Dimorphism: male larger; sexes shaped differently

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.

Range length: 109.5 (high) cm.

Other Physical Features: ectothermic ; heterothermic ; bilateral symmetry

Sexual Dimorphism: male larger; sexes shaped differently

Length: 102 cm

Holotype for Thamnophis radix
Catalog Number: USNM 719
Collection: Smithsonian Institution, National Museum of Natural History, Department of Vertebrate Zoology, Division of Amphibians & Reptiles
Sex/Stage: Female;
Preparation: Ethanol
Locality: Racine, Wisconsin, United States, North America

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. Where they are found along with their close relative Thamnophis sirtalis, they may be found in more dry habitats. This is because Thamnophis sirtalis out-compete plains garter snakes for the more moist habitats.

Habitat Regions: temperate ; terrestrial

Terrestrial Biomes: savanna or grassland

Other Habitat Features: urban ; suburban ; riparian

Habitat and Ecology

Systems

• Terrestrial
• Freshwater

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

Other Habitat Features: urban ; suburban ; riparian

Comments: This snake often occurs in the vicinity of ponds, sloughs, marshes, lakes, or slow creeks or rivers, generally in prairie and farmland areas but also in the pinyon-juniper zone; it often disperses into adjacent terrestrial habitats, such as vacant lots, residential areas, old dumps, or prairie (Rossman et al. 1996, Hammerson 1999, Ernst and Ernst 2003, Stebbins 2003). Hibernation sites incude burrows of rodents or crayfish, crevices, anthills, old wells, spaces under concrete, and other similar sites; some may hibernate underwater.

Non-Migrant: No. All populations of this species make significant seasonal migrations.

Locally Migrant: No. No populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).

Locally Migrant: No. No populations of this species make annual migrations of over 200 km.

Plains garter snakes eat a wide variety of animal prey. The diet of plains garter snakes and Thamnophis sirtalis is very similar, so they probably compete for prey where they are found in the same area. They eat frogs and toads, salamanders, fish, birds, small Rodentia, Hirudinea, Oligochaeta, and Orthoptera. Amphibians eaten include Acris crepitans, Bufo americanus, Bufo cognatus, Hyla, Pseudacris triseriata, Rana blairi, Rana pipiens, and various Caudata. They also eat Gambusia affinis, Phoxinus erythrogaster, Pimephales notatus, Riparia riparia, and Sturnella magna. Plains garter snakes find prey by following scent trails, then grabbing prey once they catch up with them.

Animal Foods: birds; mammals; amphibians; fish; insects; terrestrial worms

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 (Anaxyrus americanus americanus), great plains toads (Anaxyrus cognatus), tree frogs (Hyla species), striped chorus frogs (Pseudacris triseriata), plains leopard frogs (Lithobates blairi, northern leopard frogs (Lithobates pipiens), and various salamanders. They have been recorded eating mosquitofish (Gambusia marshi), southern redbelly dace (Chrosomus 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

Primary Diet: carnivore (Eats terrestrial vertebrates, Piscivore )

Comments: Eats amphibians, fishes, small mammals, insects, earthworms, and carrion (Stebbins 1985).

Plains garter snakes are important predators of amphibians, earthworms, leeches, and other animals in their prairie habitats.

Plains garter snakes may be preyed on by birds of prey, such as Buteo lineatus, Buteo swainsoni, Falco sparverius, and Circus cyaneus. Other predators include Vulpes, Canis latrans, Mephitis mephitis, Neovison vison, Felis catus, and Lampropeltis triangulum. Humans also sometimes kill prairie garter snakes. These garter snakes will bite, emit a foul smell, 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, and waving the tail.

Known Predators:

• red-shouldered hawks (Buteo_lineatus)
• Swainson's hawks (Buteo_swainsoni)
• kestrels (Falco_sparverius)
• northern harriers (Circus_cyaneus)
• foxes (Vulpes)
• coyotes (Canis_latrans)
• striped skunks (Mephitis_mephitis)
• mink (Neovison_vison)
• domestic cats (Felis_catus)
• milk snakes (Lampropeltis_triangulum)

Anti-predator Adaptations: cryptic

Plains garter snakes are important predators of amphibians, earthworms, leeches, and other animals in their prairie habitats.

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.

Known Predators:

• red-shouldered hawks (Buteo lineatus)
• Swainson's hawks (Buteo swainsoni)
• kestrels (Falco sparverius)
• northern harriers (Circus cyaneus)
• foxes (Vulpes)
• coyotes (Canis latrans)
• striped skunks (Mephitis mephitis)
• mink (Neovison vison)
• domestic cats (Felis catus)
• milk snakes (Lampropeltis triangulum)

Anti-predator Adaptations: cryptic

Note: For many non-migratory species, occurrences are roughly equivalent to populations.

Estimated Number of Occurrences: 81 to >300

Comments: This species is represented by a very large number of occurrences (subpopulations) (Walley et al. 2003).

100,000 to >1,000,000 individuals

Comments: Adult population size is unknown but undoubtedly exceeds 100,000. This snake is very common in many parts of its large range.

Population density estimates in different areas range from about 50 to several hundred per ha. In northern Illinois, density was estimated at 40 or 107 adults per hectare, depending on the method used (Stanford and King 2004).

In northern Illinois, adult females had a higher annual survival rate than did adult males (0.45 vs 0.35) (Stanford and King 2004).

Plains garter snakes use their sense of smell mostly. They find prey, mates, and hibernation sites by following scent trails. They also use vision and vibrations to help find their way around, avoid predators, and find prey.

Communication Channels: tactile ; chemical

Perception Channels: visual ; polarized light ; tactile ; vibrations ; chemical

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.

Communication Channels: tactile ; chemical

Perception Channels: visual ; polarized light ; tactile ; vibrations ; chemical

Comments: Active from April to November in north (Vogt 1981), March to November in south (Tennant 1984). Diurnal in mild weather, active day or night in hot summer weather (Hammerson 1982).

Plains garter snakes grow approximately 1.1 cm per week during their first year, after which growth slows.

Plains garter snakes grow at a rate of approximately 1.1 cm per week during their first year. Growth rates slow in subsequent years.

A captive plains garter snake was recorded living to almost 8 1/2 years.

Range lifespan

Status: captivity: 8.5 (high) years.

A captive plains garter snake was recorded living to almost 8 1/2 years.

Range lifespan

Status: captivity: 8.5 (high) years.

Maximum longevity: 8.4 years (captivity)

Males find females by using scent trails left by the females. 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. 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.

Breeding interval: Plains garter snakes breed once yearly.

Breeding season: Plains garter snakes breed in April or May.

Range number of offspring: 5 to 60.

Average number of offspring: 10-20.

Range gestation period: 83 to 102 days.

Range birth mass: 0.93 to 2.48 g.

Range age at sexual or reproductive maturity (female): 2 to 3 years.

Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; viviparous

Females give birth to live young. After the young are born, they do not need the help of either parent.

Parental Investment: pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Female)

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.

Breeding interval: Plains garter snakes breed once yearly.

Breeding season: Plains garter snakes breed in April or May.

Range number of offspring: 5 to 60.

Average number of offspring: 10-20.

Range gestation period: 83 to 102 days.

Range birth mass: 0.93 to 2.48 g.

Range age at sexual or reproductive maturity (female): 2 to 3 years.

Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); 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)

Gives birth to litter of 5-92 (usually fewer than 40), July-September; average litter size increases with female age/size (Stanford and King 2004); most become sexually mature at two years of age (Fitch 1970, Stanford and King 2004). In Illinois, most individuals lived not more than 6-7 years (Stanford and King 2004).

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 0
Specimens with Barcodes: 3
Species With Barcodes: 1

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.

IUCN Red List of Threatened Species: least concern

US Federal List: no special status

CITES: no special status

State of Michigan List: no special 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.

US Federal List: no special status

CITES: no special status

State of Michigan List: no special status

IUCN Red List of Threatened Species: least concern

Canada

Rounded National Status Rank: N5 - Secure

United States

Rounded National Status Rank: N5 - Secure

Rounded Global Status Rank: G5 - Secure

Population

Population Trend

Global Short Term Trend: Relatively stable (=10% change)

Comments: Extent of occurrence, area of occupancy, number of subpopulations, and population size probably are relatively stable.

Global Long Term Trend: Increase of 10-25% to decline of 30%

Major Threats

Comments: No major threats are known. This species tolerates a good deal of habitat alteration. Many are killed on roads or by mowing equipment, but this does not constitute a major threat.

Conservation Actions

Global Protection: Many to very many (13 to >40) occurrences appropriately protected and managed

Comments: Many occurrences are in protected areas.

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.

Plains garter snakes are important members of the native prairie habitats they are found in.

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.

Plains garter snakes are important members of the native prairie habitats they are found in.

Comments: Walley et al. (2003) did not recognize subspecies.