Night snakes are small, usually less than 66 centimeters in length. They have vertical pupils and bronze-copper colored eyes. Dorsal coloration consists of a tan ground color with darker brown saddle-shaped spots and lateral spots. The head is also dark brown, with the color stretching from the eyes to the base of the head where it forms a dark blotch, contrasting with the cream colored labial area. Ventral areas are pearly white (often iridescent). They are rear fanged and only mildly venomous. There is no seasonal variation in this species, but they do exhibit sexual dimorphism, with females up to three times longer than males. Night snakes are geographically widespread, with 17 sub-species currently recognized. Each may differ slightly in the above morphological characters and original type description, particularly with regards to patterns of nuchal color blotches, dorsal spots, and scale counts. (Diller and Wallace, 1986; Gregory, 1996)
Night snakes are typically found from southern Mexico in the state of Guerrero (including Sinaloa, Nayarit, Jalisco, Colima, Michoacan, Guerrero, West Puebla, Morelos, and Aguascalientes) north through much of the western United States (northeastern Baja, California, Arizona, western Colorado, Utah, Nevada, eastern California, southern Idaho, Oregon and Washington) and into south central British Columbia, Canada. They have also been found in Texas, Kansas, and Oklahoma. Though widely distributed, night snakes are considered rare in many parts of their geographic range. (Uetz and Hallermann, 2012; Weaver, 2008)
Night snakes are found in a variety of habitats (some more commonly than others), including rocky canyons (talus and scree), oak woodlands, savannahs, brushy flatlands, prairies, grasslands, croplands, and occasionally moist mountain meadows. They may be found hiding under surface debris or rocks and in crevices. Night snakes may be found from sea level up to 2650 meters above sea level and prefer arid or semi-arid habitats. (Goldberg, 2001; Hammerson, et al., 2012; Weaver, 2008)
Little is known about the development of night snake specifically, but it is likely that they follow the development pattern of other small snake species. After fertilization, females lay a clutch of 2-6 eggs, often in sandy soil. Young develop inside the egg, nourished by yolk, for 50-60 days, depending on temperature. When they hatch, young are independent and resemble small adults. (Goldberg, 2001; Pizzato, et al., 2008)
There is no information currently available regarding specific mating behaviors of night snakes. However, it is possible that males compete for mates, as seen in a related species, Imantodes cenchoa. It is likely that females produce only one clutch of eggs in a breeding season and therefore that this species is polygnous, or possibly monogamous. (Goldberg, 2001; Pizzato, et al., 2008)
These snakes are capable of breeding from spring through early fall (April-September). Clutch size may range from 2-6 eggs (averaging 3) and there is no evidence that females produce more than one clutch of eggs in a breeding season. The smallest sexually mature male recorded measured about 237 millimeters SVL (snout-vent length), while the smallest sexually mature female recorded measured 310 mm SVL, suggesting that males reach sexual maturity earlier than females. Age at sexual maturity also likely varies depending on geographic location. Young are independent upon hatching. (Diller and Wallace, 1986; Dundee, 1950; Goldberg, 2001; Lieb and Clark, 1973; Pizzato, et al., 2008)
This species is not known to exhibit any parental investment after eggs are laid. (Lieb and Clark, 1973)
Night snake are crepuscular and nocturnal, and are found in burrows or rocky crevices during the day. They are solitary animals outside of breeding, though any particular area may have multiple night snakes as residents. (Diller and Wallace, 1986)
There is no evidence that night snakes have specified home ranges or defend territories. (Diller and Wallace, 1986)
Night snakes have cat-like eyes with vertical pupils and larger cornea and lens apertures than diurnal snakes. Snakes mainly use their olfactory and vomeronasal systems to sense their environments. They use their forked tongues to draw air into pits in the roofs of their mouths, where neuroreceptors detect chemicals and other elements of their environments. They have well-developed senses of hearing, picking up sounds as vibrations along their bodies. They also have highly developed tactile receptors. (Mulcahy, 2007; Roots, 2006)
Night snakes use mild venom to subdue small prey. They are nocturnal hunters and prey items include scorpions, lizards (Bipes biporus, Cnemidophorus tigris, Coleonyx variegatus, Dipsosaurus dorsalis, Elgaria multicarinata, Sceloporus graciosus, Uta stansburiana, Xantusia vigilis) and their eggs (particularly of Uta stansburiana), salamanders (Batrachoseps sp.), frogs (Pseudacris sp.), toads (Incilius alvarius, Scaphiopus couchii, Spea hammondii), other snakes (Crotalus viridis), and insects. They are also known to occasionally eat carrion and may eat animals that wander into their daytime hiding places. (Diller and Wallace, 1986; Rodriguez-Robles, et al., 1999)
These snakes hide during the day, avoiding predation by many species. Night snakes are likely preyed upon by owls, noctural mammals, and other snakes. They are a known prey item of red-tailed hawks. (Diller and Wallace, 1986; "Night Snake: Hypsiglena torquata", 2012)
Night snakes prey on multiple small vertebrate and invertebrate species, helping to control the populations of these animals. They also serve as prey to other vertebrate species such as birds and reptiles. (Diller and Wallace, 1986; Weaver, 2008)
Texas night snakes (Hypsiglena torquata texana), a subspecies of night snake, has venom known to cause pain and possible hemorrhage in humans. (Vest, 1988)
Night snakes are nocturnal and live in areas mostly uninhabited by humans; there is no known positive economic importance for humans outside of scientific research, where studies have been conducted to test venom concentration as well as to analyze the systematics of the Hypsiglena torquata species complex. (Weaver, 2008)
Night snakes are classified as a species of "Least Concern" by the International Union for Conservation of Nature and Natural Resources due to their wide distribution and stable population size. (Hammerson, et al., 2012)
Samuel Burrell (author), Hobart & William Smith Colleges, Jim Ryan (editor), Hobart & William Smith Colleges, Jeremy Wright (editor), University of Michigan-Ann Arbor.
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Weaver, R. 2008. Distribution, abundance, and habitat associations of the night snake (Hypsiglena torquata) in Washington state. Northwestern Naturalist, 89: 164-170. Accessed February 20, 2012 at http://www.academia.edu/378705/Distribution_abundance_and_habitat_associations_of_Hypsiglena_chlorophaea_in_Washington_State.
Weaver, R. 2009. Microhabitat and prey odor selection in Hypsiglena chlorophaea. Copeia, 2009/3: 475-482. Accessed February 20, 2012 at http://www.asihcopeiaonline.org/doi/abs/10.1643/CE-08-094.