The Desert Night Snake is British Columbia's
only opisthoglyphous (rear-fanged) venomous snake. It is one of the
smallest snakes in British Columbia with a total adult length around
305-500 mm.
This slender blotched snake could be mistaken for a juvenile racer,
gophersnake or rattlesnake, but close examination reveals its distinguishing
features. The slender tail without a rattle or "button"
(the first segment of rattle on a newborn rattlesnake) distinguishes
this species from a rattlesnake, as does the shape of the head,
and its smooth body scales.
Night Snakes have unique dark markings on their neck, which may
be fused into a continuous dark blotch, several distinct blotches,
or interconnected blotches. Night Snakes also have a dark stripe
through the eye which parallels the white upper lip scales. The
eye has a vertical pupil, like that of the Western Rattlesnake and
the stout-bodied, uniformly-coloured Rubber Boa.
Distribution
Map
Red dots indicate specimen records or confirmed breeding sites.
British Columbia
The Night Snake which occurs in BC probably belongs to the subspecies,
Hysiglena torquata deserticola, the Desert Night Snake.
Only 30 specimens have been positively identified in BC since the
species was discovered here in 1980, all south of Penticton in the
southern Okanagan Valley. The southern-most locality record in BC
is approximately 130 km north of the nearest Washington state record.
North America
In Canada, the Night Snake is only found in a small portion of the
Similkameen and Okanagan river valleys in the BC interior, and is
considered to be one of the rarest snakes in the country. However,
its rarity may stem more from its secretive nature than actual population
size.
In the USA, Night Snakes are wide-spread throughout 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, and northern
Mexico. Records of Night Snakes in Central America and Costa Rica
are based on misidentifications. 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 as it searches for prey. This
species occurs in a variety of habitats but is associated with arid
sandy and rocky habitats
All British Columbia specimens have been taken near talus
slopes, under rocks in greasewood
habitat up-slope of the valley floor. Other vegetation in the immediate
vicinity of record sites include: saskatoon, bunchgrass, chokecherry,
poison ivy and sage.
While the habitat for this species remains
relatively intact, the native flora and fauna of Okanagan river
valleys has been severely altered by humans. Research 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 is correct, then there has been a significant loss of habitat
due to development in the Okanagan and Similkameen valleys. Other
factors, such as scarcity of suitable hibernacula,
also may restrict the species' distribution at lower elevations.
Why is it endangered?
Little is known about the factors governing the distribution of
Night Snakes, except that they may include competition, predation,
prey availability, or human disturbance. Their nocturnal
nature ensures that most Night Snakes go unseen, and so their main
threat from humans is habitat destruction, rather than active persecution
(as is the case with larger, diurnal species such as rattlesnakes
or gophersnakes). Unfortunately, the talus slope habitat and benches
along the Okanagan and Similkameen valleys are being used as a source
of fill and rip-rap, as well as sites for development, and so this
further reduced available habitat for Night Snakes in BC.
Climate is probably an important limiting factor affecting population
size and distribution. Oviparous
snakes in British Columbia, and in Canada generally, have a more
restricted range in the south compared to 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. Once oviparous species have laid
and abandoned their eggs, they have no control over development.
Their eggs develop as local weather dictates, and prolonged wet,
excessively hot, or cold conditions can cause nest failures. In
contrast, live-bearing snakes retain eggs and females bask in the
sun to control the rate of development of their young by optimizing
their own body temperatures.
Biology
Breeding
Night Snakes may lay eggs between April and August. In Idaho they
are known to lay eggs in June. Night snakes may produce two clutches
per year, which would explain the wide range of egg-laying dates,
and they deposit 2 to 9 eggs. As of 2006, we have no data on reproductive
rate, growth rate of individuals, or Night Snake population trends
in British Columbia.
Behaviour
The Night Snake is secretive and nocturnal, and solittle is known
about its behaviour.
Diet or Growing requirements
The Night Snake is the only rear-fanged venomous snake in British
Columbia. The fangs consist of enlarged teeth at the back of the
upper jaw and are only slightly grooved to transmit venomous saliva.
The saliva is toxic to the snake's usual prey and is worked into
the prey when grasped, accompanied by a "chewing" motion.
This venom appears toxic to amphibians and can paralyse small lizards
within seconds, although more time is required for death to occur.
Small frogs may simply be swallowed whole and alive. Desert Night
Snakes also feed on eggs, juveniles and adults of small lizards
and snakes (including young rattlesnakes) and 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
tree frogs, whereas others freely take snakes, lizards and frogs
when offered without even bothering to chew and inject their venomous
saliva. A night snake captured in 1989 also fed on treefrogs. One
captive Night Snake regurgitated a young rattlesnake.
The venom is not known to be dangerous to humans, and 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
Museum Specimens
this section sponsored
by: 
Industry Canada
