The Desert Night Snake is a slender, small to medium-sized snake with adult length typically 25 – 53 cm (COSEWIC 2001). Larger individuals, up to about just over 60 cm long, are occasionally encountered (St. John 2002) and appear to be more common within the northern portion of the species’ range, including British Columbia (COSEWIC 2001, Matsuda et al. 2006). The head is flat and somewhat triangular, and the pupils of the eyes are vertical, indicative of night vision. The body scales lack keels, giving the snake a smooth appearance. The ground colour of the back and sides is tan, grey, or light brown with a distinct pattern of dark brown, almost square-shaped blotches. There is a row of larger blotches along the mid-back and rows of smaller blotches along the sides. The underside is glossy white or yellowish. A dark stripe from the nostril extends across the eye to the neck, forming a facial mask. A dark brown “collar” around the neck, consisting of two or three blotches, is diagnostic (St. John 2002, Matsuda et al. 1986). The Desert Night Snake superficially resembles other sympatric snakes with a blotchy colour pattern. Unlike small Gopher Snakes and juveniles of the much larger Racer with which it may be confused, the Night Snake has vertical rather than rounded pupils; the Western Rattlesnake also has vertical pupils, but the Night Snake has smooth rather than keeled body scales and lacks a rattle at the end of the tail.
Virtually nothing is known of the life history and reproductive biology of the Desert Night Snake in British Columbia, and there is only scant information for this and other species of Night Snakes in the United States. Night Snakes are oviparous and lay eggs. Storm and Leonard (1995) give the clutch size as 3 – 9 eggs. Females grow larger than females. In southwestern Idaho, the snout-vent length of six sexually mature females was 494 ± 19 mm, while that of 41 mature males was 331 ± 5 mm (Diller and Wallace 1986). The age at maturity is unknown. Little information on survivorship and longevity is available, but the snakes can live at least 4 – 5 years (COSEWIC 2001).
Diet
Night Snakes are thought to feed largely on small lizards but will also take a variety of other prey, such as amphibians, small snakes, and insects (Matsuda et al. 2006). These snakes are mildly venomous and subdue their prey with venom associated with specialized, enlarged teeth at the back of the upper jaw. Reflecting their mode of venom delivery, they are termed rear-fanged snakes.
Behaviour
Night Snakes are secretive and mostly nocturnal or crepuscular, and as a result are seldom seen, even where known to be present. Night-cruising through appropriate habitats on warm nights has been used with success to locate the species (Storm and Leonard 2005, Weaver 2008).
Seasonal Charactertistics
In British Columbia, the Desert Night Snake has been observed from June to early September (COSEWIC 2001). The snakes hibernate during cold periods in the winter, but there are no records of the species from communal dens used by other snakes or from other any sites in British Columbia (COSEWIC 2001). Mating probably takes place in spring, oviposition in early summer, and hatching of young in early autumn, but no details are available (COSEWIC 2001).
In British Columbia, the Desert Night Snake occupies shrub-steppe habitats in hot, arid southern interior valleys, including near desert-like areas (COSEWIC 2001). The snakes have been found within talus slopes and rock outcrops, which appear to be important habitat features for the species. The snakes may also shelter in rodent burrows, as documented in Idaho (Diller and Wallace 1986).
The distribution of the Desert Night Snake extends from southern British Columbia along the Pacific Coast to California and inland to Idaho in the north and Colorado and New Mexico in the south (NatureServe 2009, Mulchahy 2008). The clade H. chlorophaea also extends south to northwestern Mexico (Mulchany 2008). The species reaches its northern limits of distribution in British Columbia, where it is known only from the South Okanagan and Lower Similkameen Valleys (COSEWIC 2001). The snake appears to be very rare in the province with less than 30 confirmed records (Matsuda et al. 2006). In Washington State, road-cruising at night has shown them to be more abundant in suitable habitats than previously thought (Weaver 2008). How much the secretive and nocturnal habits of the snakes contribute to their apparent rarity in British Columbia is unknown.
The Desert Night Snake has small distribution in British Columbia, coinciding with a populated area experiencing urban and agricultural expansion. COSEWIC (2001) listed the following threats to Canadian populations of the snake: urban/agricultural developments; loss and fragmentation of habitat; pollution (pesticides); mortality on roads; and isolation of populations. The species is nationally endangered and on Schedule 1 (highest priority) of the Canada Species At Risk Act. Recovery of the species is coordinated by the South Okanagan-Similkameen Conservation Program, which facilitates habitat stewardship and multispecies conservation initiatives.
This species was formerly known as Hypsiglena torquata (Night Snake), but this name has now been assigned to populations in Mexico (Mulcahy 2008). Genetic data have revealed that the taxon formerly known as H. torquata represents several sister species (Mulchany 2008). Consequently, Collins and Taggard (2009) listed four species of Night Snakes from North America, north of Mexico: Hypsiglena chlorophaea Cope, 1860 (Desert Night Snake), Hypsiglena jani (Dugés, 1865) (Chihuahuan Night Snake), Hypsiglena ochrorhynchus Cope, 1860 (Coast Night Snake), and Hypsiglena sp. (undescribed) (Hooded Night Snake). The species that occurs in British Columbia is H. chlorophaea. The Night Snake was formerly placed in the large cosmopolitan family Colubridae, which recently has been split. Its placement in the family Dipsadidae follows standard nomenclature listed by Collins and Taggard (2009).
