Plains gartersnake (Thamnophis radix)

Plains gartersnake showing tongue
IUCN Red List species status – Least Concern LEAST

Top facts

  • Although the Plains gartersnake is venomous, its toxic secretions have no effect on humans.
  • The female Plains gartersnake stores the sperm of the male over the hibernation period until the following spring, when it allows its eggs to be fertilised.
  • Although the female Plains gartersnake usually gives birth to 30 young, up to 92 have been reported in a single litter.
  • While hibernating, the Plains gartersnake inhabits old mammal and crayfish burrows.
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Plains gartersnake fact file

Plains gartersnake description

GenusThamnophis (1)

The Plains gartersnake (Thamnophis radix) is a medium-sized, slender snake with a green-grey, olive, brown or occasionally red upper surface (2) (3), which has a bright yellow or orange stripe running along the centre (3). On either side of the central stripe, there are two rows of dark blotches, which form a checker-like pattern (3). Along the sides of the Plain’s gartersnake’s body there are horizontal green or cream-blue stripes (2), which are positioned alongside two rows of round, black spots (4). The underside may be whitish, blue-green or grey (2) (3) and is also patterned with two rows of dark spots (3). The top of the head is black or dark brown, while the chin and throat are pale yellow (4). The female Plains gartersnake is generally larger than the male (3).

Some taxonomists recognise one or two subspecies of Plains gartersnake (2) (3): Thamnophis radix haydeni and Thamnophis radix radix (3).

Also known as
plains garter snake.
Total length: 38 - 70 cm (2)

Plains gartersnake biology

Most mating occurs in April and May, and the female stores the sperm during hibernation until the following spring, when it allows its eggs to be fertilised. The male Plains gartersnake finds a receptive female by following its sex pheromone, and small mating balls may occasionally be formed with between four and six males and one female. Once it has mated with a female, the male may place a copulatory plug into her cloaca, to attempt to prevent any other males from fertilising the eggs (4). The female Plains gartersnake gives birth to live young (3) after a 9-week gestation period (4), with clutches usually containing 9 to 30 young (4). Generally, larger females have clutches with a higher number of young than smaller females (4). Sexual maturity is attained in the second or third year of life (2).

The diet of the Plains gartersnake consists mostly of earthworms and frogs, with toads, leeches, slugs, carrion (4), fish, amphibians and small mammals such as mice and shrews also being taken secondarily (3) (4). The diet of this species is seasonally variable and depends on the availability of prey in the area (4). A mildly venomous species, the Plains gartersnake immobilises its prey by injecting it with a toxic secretion, although this is not harmful to humans (3).

The active season of the Plains gartersnake runs between mid-March (4) and October (3) (4), although this is dependent on which area the individual occupies, and some populations may become active later in the year. During the period of activity, the Plains gartersnake is diurnal (4).


Plains gartersnake range

The Plains gartersnake is found in Canada and the United States, from Alberta, Saskatchewan and Manitoba in the north, through the Great Plains to north-eastern New Mexico, western Oklahoma and northern Texas (1) (2) (3) (4).


Plains gartersnake habitat

The Plains gartersnake occurs in a range of habitats (3), although it is most regularly found in areas in close proximity to ponds, lakes, streams, marshes (1) (3), sloughs and dugouts. It is also often found in neighbouring terrestrial habitats such as residential areas or prairies (3). During hibernation it inhabits mammal or crayfish burrows, crevices, anthills and old wells. This species is found at elevations between 120 and 2,290 metres, but usually remains at elevations below 1,830 metres (1).


Plains gartersnake status

The plains gartersnake is classified as Least Concern (LC) on the IUCN Red List (1).

IUCN Red List species status – Least Concern


Plains gartersnake threats

The Plains gartersnake is not currently thought to be threatened, although many unnatural deaths are caused through collisions with moving traffic (1) and agricultural activities such as grass burning and mowing (1) (4). In urban areas, wild populations have been drastically reduced due to construction and pesticide use (2).


Plains gartersnake conservation

The Plains gartersnake is listed as a state endangered species in Ohio (4), and it occurs in many protected areas throughout its range (1). Although there are not currently known to be any conservation measures in place for this species, it has been proposed that mowing operations should be modified to prevent unnecessary mortalities from occurring, and more research should be done into the species to attain better knowledge of its range, biology and the main causes of mortality (4).


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The flesh of a dead animal.
A common cavity into which the reproductive, digestive and urinary systems open in birds, reptiles, amphibians, most fish and some primitive mammals.
Active during the day.
The fusion of gametes (male and female reproductive cells) to produce an embryo, which grows into a new individual.
The state of being pregnant; the period from conception to birth.
A winter survival strategy in which the animal passes the winter in a resting state. This period of inactivity is characterised by specific biological and biochemical changes including lowered blood pressure and respiration rate. In reptiles, this is also known as brumation.
A chemical produced by an animal, which stimulates a behavioural or physiological response by another member of the same species.
An extensive area of flat or rolling, predominantly treeless grassland, especially the large tract or plain of central North America.
A population usually restricted to a geographical area that differs from other populations of the same species, but not to the extent of being classified as a separate species.


  1. IUCN Red List (January, 2013)
  2. Degenhardt, W.G., Painter, C. W. and Price, A.H. (1996) Amphibians and Reptiles of New Mexico. University of New Mexico Press, Albuquerque, New Mexico.
  3. Russell, A.P. and Bauer, A.M. (2000) The Amphibians and Reptiles of Alberta: A Field Guide and Primer of Boreal Herpetology. University of Calgary Press, Calgary, Alberta.
  4. Reichenbach, N., Barrie, M., Becka, K., Burghardt, G. and Butterworth, S. (2010) Ohio Conservation Plan: Plains gartersnake, Thamnophis radix. Liberty University, Lynchburg, Virginia. Available at:

Image credit

Plains gartersnake showing tongue  
Plains gartersnake showing tongue

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