The common gartersnake is extremely variable in colouration and pattern; either stripes or spots may predominate. The species illustrated here is from eastern Ontario, Canada, and is black with lemon yellow stripes. In the Maritimes, it is gray or brown with spots, and its stripes are often obscured. In the west, from Manitoba to British Columbia, it is boldly marked with red and stripes. It is usually about 46 to 70 cm in length (18 to 27.5 in.), with the rare individual growing more than 1 m (39 in.).
The common gartersnake occupies a wide variety of terrestrial and semi-aquatic habitats such as meadows, marshes, woodlands, hillsides, along streams and drainage ditches, and in parks.
In winter, the snakes often den up in rock outcroppings or fissures in the ground beneath the frost line, sometimes by the thousands. Road embankments, mammal burrows and basements of old buildings are also common hibernacula.
This snake is active during the day and night. It eats a variety of animals such as earthworms, frogs, fish, salamanders and, occasionally, mice. The young are born live (ovoviviparous), usually 20 to 40 but sometimes more than 80 in a litter.
The common gartersnake occurs in Canada in every province except for Newfoundland; it is also found in the southern part of the Northwest Territories. It occurs in most of the United States except for the southwestern deserts, and in the northern edge of Mexico.