A variety of the garter snake of western North America, especially of the subspecies Thamnophis sirtalis parietalis, having a series of red bars along each side.
Origin
Late 19th century.
Definition of red-sided garter snake in US English:
red-sided garter snake
noun
A variety of the garter snake of western North America, especially of the subspecies Thamnophis sirtalis parietalis, having a series of red bars along each side.