DESERT NIGHT SNAKE Hypsiglena torquata deserticola Family Colubridae - modern snakes Order Squamata - lizards and snakes Risk Status Official status The Night Snake is on the Provincial Red List (CDC=G5 S1). A COSEWIC status has not yet been identified. Risk Status Distinguishing Features Distribution Habitat Why is it endangered? Biology Sources for more information Museum Specimens Image Credits: sketch in Reptiles of British Columbia, Gregory and Campbell, 1984. Photo by Andrius Valadka Historical facts Not yet available. Distinguishing features The Desert Night Snake is British Columbia's only rear-fanged venomous snake. It is one of the smallest snakes in British Columbia with a total adult length is 305-500 mm. An observer's first impression of this species is of a slender blotched snake which could be mistaken for a juvenile racer, gopher snake or rattlesnake. A close examination will reveal the easiest distinguishing marks. The slender tail and the absence of a rattle or "button" - the first segment of rattle on a newborn rattlesnake - distinguishes this species from a rattlesnake. Night snakes have a unique dark mark on their neck. This mark may be fused into a continuous dark blotch or it may be several distinct blotches or some variation in between. In examining the snake's head, the observer will note a dark bar behind the eye which contrasts clearly with the white upper lip scales. The eye has a vertical pupil; in British Columbia, only the rattlesnake and the stout-bodied, uniformly-coloured rubber boa also have vertical pupils. As well, the head appears somewhat flat and slightly triangular. Distribution Map Red dots indicate specimen records or confirmed breeding sites. British Columbia As might be expected with such a wide-ranging animal, there is considerable debate about subspecies. The Night Snake probably belongs to the race, Hysiglena torquata deserticola, the Desert Night Snake. Only five records south of Penticton in the southern Okanagan Valley have been found. Known sites for this species remain relatively undisturbed and moderately inaccessible. The most southerly of these records is approximately 130 km north of the most northerly Washington state record. North America In Canada, the Night Snake is only found in British Columbia, being one of the rarest snakes in the country. In the U.S.A. however, it is widely distributed throughout western North America, from central Washington, eastern Oregon, southern Idaho, Nevada, southwest Kansas, northern Utah, and across the southern United States from northern California to the south tip of Baja California and central Texas; south throughout mainland Mexico and Central America to Costa Rica. In the northwest, it is found in the Columbia Basin, Snake River, and southwest Klickitat County in Washington State. Habitat The Night Snake is usually found under rocks or other cover, but may be seen crossing roads at night when it forages for prey. This species occurs in a variety of habitats but is generally associated with arid regions, especially sandy and rocky habitats. All British Columbia specimens have been taken in the vicinity of extensive talus slopes under rocks in greasewood habitat up from the valley floor. Other vegetation in the immediate vicinity of record sites include: saskatoon, bunchgrass, chokecherry, poison ivy and sage. While the habitat in which this species has been recorded in the last decade remains relatively intact, the original valley vegetation has been severely altered by humans. The literature suggests that this species might have occupied the Ponderosa Pine-Bunchgrass zone of the valley bottom as well as the talus slopes and higher elevations. If this were the case, then there has been a significant loss of habitat over the course of development in the valley. It is possible, however, that other factors, such as scarcity of suitable hibernacula, might restrict the species' distribution at lower elevations. Why is it endangered? Little is known about the limiting factors except that they may include competition, predation, prey availability, or human disturbance. Their nocturnal nature suggests that the Night Snake's main threat from humans is in terms of habitat destruction rather than active persecution as is the case with larger, diurnal species such as rattlesnakes or gopher snakes. Talus slopes and benches along the valley are being used as a source of fill and rip-rap, as well as sites for development as a result of the increasing population pressures in the Okanagan. Climate is probably an important limiting factor affecting population size and distribution. Oviparous snakes in British Columbia, and in Canada generally, have a significantly more restricted range than viviparous species. All egg-laying snakes in British Columbia - with one exception - are restricted to the southern portion of the province, and particularly to the hot, dry southern interior. This pattern is probably the result of these species' thermoregulatory needs for reproduction. Live-bearing snakes can behaviourally control the development of their young by optimizing their own body temperatures. Once oviparous species have laid their eggs, they have no further control over development. These eggs are then vulnerable to the weather trends which often include wet or cold conditions. These conditions could be detrimental or fatal to egg development. Biology Breeding The general literature suggests that egg-laying may take place between April and August. Night snakes may produce two clutches per year which would explain the wide range of egg-laying dates but the breeding frequency is unknown in British Columbia. They lay between two to nine eggs. No information is available of the reproductive rate, recruitment potential, or growth potential of this species in British Columbia. Behaviour The Night Snake is secretive and nocturnal. They may congregate to hibernate, but no data is available to confirm this. Diet or Growing requirements The Night Snake is the only example of a rear-fanged venomous snake in British Columbia. The fangs are enlarged teeth at the back of the upper jaw and are only slightly grooved if at all. The saliva is toxic to the snake's usual prey and is conducted into the prey along the fangs when grasped, accompanied by a "chewing" motion. This venom is apparently toxic only to amphibians and can paralyse small lizards within seconds, although much more time may be required for death to occur. Small frogs may simply be swallowed whole and alive. Desert Night Snakes also feed on small lizards, snakes and their eggs, toads, salamanders, centipedes, scorpions and insects. A night snake captured in British Columbia in 1988 refused juvenile alligator lizards but accepted juvenile western toads and Pacific treefrogs. The night snake captured in 1989 also fed on treefrogs. Toads and treefrogs are common species in southern British Columbia. The venom is not known to be dangerous to humans, unlike that of some large rear-fanged snakes in other parts of the world. In any case, the Night Snake is small and rarely, if ever, attempts to bite when handled. Predators No information is available at this time. Sources for more information Related On-line Sites to Visit Publications Reptiles of BC, RBCM, Gregory and Campbell, 1984, p.88 The SOCAP Workshop Summary, The Nature Trust, 1989 Provincial Status Report, Parsons, March 1991 Living Landscape Directory of Researchers and their projects Museum Specimens this section sponsored by: Industry Canada

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