Thamnophis sirtalis (Linnaeus, 1758)
Key Characters: Side stripes on scale rows 2-3; yellow or gray midback stripe; black bars on margins of labial scales; back scales strongly keeled; anal scale not divided.
Similar Species: Eastern Ribbonsnake, Western Ribbonsnake, Plains Gartersnake, Lined Snake.
Subspecies: Twelve subspecies are currently recognized, but only two, Eastern Gartersnake, T. s. sirtalis and Chicago Gartersnake, T. s. semifasiatus (Cope, 1892) occur in Illinois.
Description: Medium-sized (up to 100 cm TL) dark brown or black snake with a yellow or gray midback stripe and a yellow stripe on each side. Belly gray-green with dark spots on edges of most belly scales. Head usually without parietal light spots. Some individuals have red coloring between side scales. In the Chicago region, the side stripe near the head is broken into a dashed line by black crossbars (Chicago Gartersnake, T. s. semifasciatus).
Habitat: Forests and edge habitats, commonly near water. Vacant lots in cities.
Natural History: Cold-tolerant snake that occasionally emerges from hibernation to bask on warm winter days. Mates immediately after emerging from hibernation, as early as March in southern counties. Females give birth to 15-80 young from July through early October that are 15-20 cm TL. Diet includes fish, amphibians, young birds, and a variety of invertebrates. Eaten by a wide variety of predatory vertebrates; people needlessly kill many.
Status: Common throughout the state.
Etymology: Thamnophis – thamnos (Greek) meaning shrub, bush; ophio (Greek) meaning serpent, reptile; sirtalis – (New Latin) meaning ‘like a garter’; semifasciatus – semi (Latin) half and fasciatus (Latin) banded.
Original Description: Linnaeus, C. 1758. Systema Naturae per Regina tri Naturae secundum Classes, Ordines, Genera, Species, cum Characteribus, Differentiis, Synonymis, Locis. 10th ed. Salvii, Stockholm. 1:824 pp. For semifasciatus, Cope, E.D. 1892. A critical review of the characters and variations of the snakes of North America. Proc. US Natl. Mus. 14: 589-694.
Type Specimen: Holotype. Lost. For semifasciatus, Syntypes. USNM 8070.
Type Locality: “Canada”. For semifasciatus, “Aux Plaines, Illinois”.
Original Name: Coluber sirtalis Linnaeus, 1758. For semifasciatus, Eutaenia sirtalis semifasiatus Cope, 1892
Nomenclatural History: Like most of the gartersnakes, this species has a very complicated nomenclatural history. It was transferred to the genus Eutainia, which is how Kennicott (1855) listed it. Davis & Rice (1883) used Eutaenia.