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The distribution of the Plains Gartersnake runs through the Great Plains from southern Canada into Montana, North Dakota, and Minnesota south through Colorado and Kansas into northeastern New Mexico, Texas, and Oklahoma. In Wyoming it is found the grassland communities of the prairie life zone in the northeast and along the eastern edge of the state below 6,500 feet. It is generally associated with the riparian margins along small streams and sloughs, and the marsh and cattail pond habitats of wetlands.
They are active from late April into October, feeding on insects, earthworms, frogs, toads, small fish and mammals; they may aggregate in large numbers feeding on a common and abundant food source. They are primarily diurnal but will forage at night during hot weather. When surprised they quickly flee to heavy cover or enter the water where they can remain submerged for a long time. They are relatively docile and seldom bite; when handled they usually twist and squirm about—emptying the contents of their cloaca and smearing the foul smelling material on to the handler.
They are medium sized snakes with total lengths in the range of 20-30 inches. Females are considerably larger than males. Their scales are keeled (ridged) and overlapping. The anal plate is entire. The background is olive or dark gray-brown with 3 longitudinal stripes. The well defined dorsal stripe is a bold yellow or orange; the lateral stripes are pale yellow and located on the 3rd and 4th row of scales above the belly plates. The area between the midline and lateral stripes contains alternating rows of dark spots that form somewhat of a checkerboard pattern; this area is often very dark and the spots may be obscured. The belly is a light greenish-blue or cream and has black spotting along the lateral margins of the ventral plates. There are black bars on the posterior margins of the pale labial scales found along the upper jaw.
Mating behavior is associated with denning activities and may occur prior to dispersal in the spring or upon return when arriving in the fall. In the latter case, sperm is stored within the female’s body over winter and fertilization takes place the following spring. Multiple males pursue and court large females. Successful males leave a gelatinous (seminal) plug in the female’s cloaca, rendering her “unattractive” and preventing her from mating with other males. After a 8-9 week incubation period, a litter of 10-25 young are born alive (viviparous) in August and September. Sexual maturity is reached in the 2nd or 3rd year.