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Butler's Gartersnake

Thamnophis butleri

Family: Colubridae

COSEWIC status:
  • Endangered
SARA status:
  • Endangered
IUCN status:
  • Least Concern

Description

The Butler’s Gartersnake is one of the smallest species in the gartersnake group, reaching a maximum total length of only 69 cm, though individuals are typically less than 50 cm long. The background colour is brown to black with three yellow stripes: one down the back (dorsal stripe) and one on each side (lateral stripes). The lateral stripes are on the third and part of the second and fourth scale rows. The chin, upper jaw and belly of the Butler’s Gartersnake are yellowish. This species has a smaller head than the Eastern Gartersnake, making the neck less obvious.

Similar Species

The Butler’s Gartersnake may be confused with the Eastern Gartersnake and Eastern Ribbonsnake, both of which also occur in southern Ontario. These other two species have larger heads and a more pronounced neck than the Butler’s Gartersnake. The lateral (side) stripes on the Eastern Gartersnake are confined to the second and third scale rows. The lateral stripes on the Eastern Ribbonsnake are on the third and fourth scale rows. The Eastern Ribbonsnake also has a distinct white crescent in front of the eye, is slenderer and has a longer tail. Butler’s Gartersnakes may also be mistaken for Queensnakes, which also have two yellow lateral stripes. The Queensnake, however, has several faint dark stripes rather than a yellow stripe down the back.

Distribution

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The Butler’s Gartersnakes only occurs in a few small areas in southwestern Ontario. These small, isolated populations are probably remnants of a more continuous, historic distribution in southern Ontario. In the United States, the distribution of this species is limited to southeastern Wisconsin, Indiana, Ohio and the Lower Peninsula of Michigan.

Habitat

Historically, the Butler’s Gartersnake occurred in prairie habitats but can now be found in fields, wetland edges and other grassy areas. Like the Eastern Gartersnake, this species often inhabits urban and agricultural areas. It is frequently found under cover, such as boards or rocks, which provide important microhabitat for shelter and thermoregulation. They overwinter underground below the frost line in mammal burrows, crayfish burrows, anthropogenic structures (e.g. old foundations, cisterns), ant mounds and other underground cavities.

Biology

Butler’s Gartersnakes breed in April after emerging from hibernation. Females give birth to 8–12 live young in mid to late summer, although up to 16 young have been reported from one female. The young are roughly 15 cm in length at birth and reach sexual maturity in their second year. Butler’s Gartersnakes feed primarily on earthworms but also eat insects, slugs and frogs. Longevity in wild populations is unknown, but high adult mortality rates in southwestern Ontario populations suggest that individuals rarely live past 10 years of age.

Threats

Ongoing habitat loss due to agriculture and urban development is the primary threat to this species in Canada. The extremely limited distribution of this species and its overlap with areas of high development pressure (e.g. city of Windsor) makes it vulnerable to extirpation in Canada. Anthropogenic sources of mortality, such as persecution and being killed on roads, are also threat to this species since it occurs predominantly in areas with high human populations.

Additional Information About This Species In Canada