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Canadian Amphibian and Reptile Conservation Network - Réseau Canadien de 
Conservation des Amphibiens et des Reptiles

Pantherophis spiloides,

anciennement Elaphe obsoleta spiloides

Couleuvre Obscure / Gray Ratsnake

Couleuvre Obscure

TThe Gray Ratsnake is the largest snake in Canada, growing to 2.5 m in total length. Juveniles are distinctly blotched, with older individuals becoming increasingly black. The blotches are usually at least faintly visible in adults. The belly is whitish with black checkerboard markings. Analysis of the genetics of the former Ratsnake (Pantherophis obsoleta) resulted in the "species" being divided into three species. The species found in Ontario is now called Pantherophis spiloides.

Confusing Species
The large size and dark colouration of the Gray Ratsnake can only be confused with the Northern Water Snake, which is generally patterned, but gets darker with age. The belly of the Northern Water Snake is also whitish, but with dark crescent-shaped spots.

The Gray Ratsnake is limited to southern Ontario in Canada. It is found in two disjunct areas: the north shore of Lake Erie and the eastern end of Lake Ontario. Within the U.S., the Gray Ratsnake is found east of the Mississippi River and west of the Appalachian Mountains and as far south as the Gulf of Mexico.

Ratsnakes prefer wooded areas although they may spend part of the summer in open areas such as old fields or meadows.

Breeding occurs in spring and the females lay their eggs in rotting logs or under rocks. Up to 24 eggs can be laid, but 12-16 is more common. The eggs hatch in late summer or early fall. The hatchlings are 30-40 cm long.

Natural History
The sight of a 2 m snake draped across the branches of a tree is not expected in Canada, but the Ratsnake does frequently make use of trees. It regularly climbs trees to eat birds' eggs or nestlings. In addition to birds, it also eats small mammals and frogs. In eastern Ontario Ratsnakes hibernate communally in rocky outcrops.

Conservation Concerns
Because of their large size Ratsnakes are frequently killed by insensitive people who dislike, or fear snakes. They are also killed on roads. The small size of their range in Canada also makes them vulnerable to further decline. The population in eastern Ontario is limited to a small area, and is threatened by increasing development. This Great Lakes/St. Lawrence population has been designated Threatened by COSEWIC. The population in southwestern Ontario occupies an even smaller area and is believed to consist of only four disjunct subpopulations. This Carolinian population has been designated Threatened by COSEWIC.