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The Northern Rubber Boa is distributed from southern British Columbia through Washington, Oregon, and California, and east into Montana, Idaho, Nevada, and Utah. In Wyoming it is found at the lower elevations of the northwestern and north central foothills and montane life zones, from Yellowstone NP south along the Owl Creek Mountains, Wind River Mountains, and Wyoming Range, and the east and west slopes of the Big Horn Mountains. It is fond of the mountain stream riparian habitat within coniferous forests—especially where there are abundant flat rocks, rotting logs, accumulations of ground litter, and small nearby meadows.
They are active from May into September, foraging both at night (nocturnal) and during the hours near dawn and dusk (crepuscular), but they are secretive snakes and spend most of their time hiding under objects or in rotting logs. They feed primarily on small mammals such as shrews, voles, and mice—killing by wrapping around the body of their prey and constricting until the victim dies of asphyxiation. They are often found with scars on their tail, presumably resulting from the defensive attacks suffered by the mothers of the babies they consume.
These snakes are docile and do not bite. When alarmed they roll into a ball of coils and protect their head by tucking it beneath the loops. While in this defensive position they may elevate their tail and lash out with it in a false strike in an attempt to fool their antagonist. They are less heat tolerant than other species of snakes in Wyoming and do better in cooler environments. They are reported to live as long as 20-30 years in the wild.
It is a small, thick-bodied snake with a total length (TL) up to 24 inches. It is sometimes called a “two-headed snake” because the blunt tail is not that much different from the size and shape of the head. Both the dorsal and ventral surfaces are covered with small, smooth scales; the head is shielded with larger and irregularly shaped scales. The caudal scales and the anal plate are entire (undivided). It has a small head, without a distinct or tapered neck, and small eyes with vertically elliptical pupils. Both sexes have a pair of anal spurs which are vestigial remnants of hind limbs. These spurs may be difficult to see in females and are more distinct and slightly hooked in males. The dorsal background is dark olive or reddish to chocolate brown with a greenish or bluish sheen; the brown blends to yellow along the sides and pales to cream or white on the belly. The skin is loose fitting and forms wrinkles or folds wherever the body is curved or bent.
These snakes bear their offspring alive (viviparous) with an average brood size of 7-11 young. Mating and courtship occurs in May or early June and the young are born in late summer and early fall. During courtship males use their spurs to caress the female. Females do not reproduce every year and may wait as long as four years between breeding cycles. They reach sexual maturity at about 14 inches (unknown in years of age).
*The captive snake for these 5 images was provided by the courtesy of Wyoming Game & Fish and held under a state permit and care of Charles Plymale. All photographs copyright © Dan Lewis.