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The Smooth Greensnake is distributed in a more or less continuous range from southern Canada, North Dakota, and Minnesota south into Illinois, Ohio, and Virginia, and east into the New England states; there are additional disjunct populations occurring in Iowa, Missouri, Nebraska, Wyoming, Colorado, Utah, and New Mexico. The populations in Wyoming are found in the Black Hills, the northern Laramie Mountains near Laramie Peak and Casper Mountain, Sierra Madre Mountains, Snowy Range, and possibly the Uinta Mountains. They inhabit the foothills and lower montane life zones where they favor riparian habitat and the (mesic) ecotones where damp meadows and moist grassy areas are bordered by forests and woodlands.
These are secretive snakes that are active from May through September. They are diurnal and, when not hiding under rocks, rotting logs, and ground litter in forested areas, they forage for spiders and insects. If cornered or frustrated they threaten with mouth gaping and aggressive posturing. When handled they are very active and frequently tie the tail into a knot, but they rarely bite. They are distinguished from the garter snakes found in Wyoming by the lack of longitudinal stripes. They are identified from adult Yellow-bellied Racers by their smaller size and from juvenile racers by the lack of dark brown dorsal blotches. They often use communal dens with other species.
It is a small and slender snake with total lengths (TL) in the range of 14-18 inches; females are slightly longer than males. As its name suggests, the dorsal scales are smooth (unkeeled), polygonal shaped, and only slightly overlapping—naturally these scales are green and the uniform background may be a bright grass green or a duller olive or greenish brown. The belly is white and the anal plate is divided. It has a red tongue with a black tip.
They may use communal nesting areas under rocks, in rotting logs, or in shallow burrows where individuals lay a clutch of 3-11 eggs in late July and August. Females often retain the eggs within their body for an extended period of time and they may not deposit these eggs until a few days before hatching. Incubation requires a period of about 30 days. They become sexually mature during the 2nd or 3rd year when individuals reach 10 or more inches in length.