Reptiles
Night Snake
Hypsiglena spp. · also called night snakes
As the desert cools after sunset, a night snake finally slips out from beneath the rock where it spent the entire day hidden, its vertical, cat-like pupils opening wide to make the most of the fading light while it searches for a sleeping lizard.
Overview
The night snake, genus Hypsiglena, is a small, mildly venomous colubrid native to arid and semi-arid habitat across western North America. Its distinctive vertical pupils and strictly nocturnal lifestyle set it apart from most other snakes sharing its desert range.
Built for the dark hours only
While many desert reptiles split activity between day and night depending on temperature, the night snake commits almost entirely to darkness, an eye adaptation and behavioural pattern that keeps it hidden and rarely encountered despite being common across much of its range.
Status
Least Concern — widespread and stable across suitable arid and semi-arid habitat throughout western North America.
Night Snake: common questions
Why does the night snake have such unusual eyes?
A night snake has vertical, elliptical pupils unlike the round pupils typical of most colubrid snakes, an adaptation associated with its primarily nocturnal activity pattern, since vertical pupils generally allow for a wider range of light control useful for a species that is active mainly after dark.
Is the night snake dangerous to humans?
No, the night snake possesses only mild venom delivered through rear fangs, generally sufficient to subdue small lizards and amphibians but posing minimal risk to humans, and the species is also generally docile, typically attempting to flee or remain motionless rather than bite defensively when encountered.
Why is the night snake so rarely seen?
A night snake spends most of the day hidden beneath rocks, logs, or loose soil, only becoming active once temperatures cool in the evening and at night, a secretive, nocturnal lifestyle combined with muted camouflage colouration that makes the species considerably less frequently encountered than many diurnal snakes sharing its range.
Where does the night snake live?
The night snake is native to a range of arid and semi-arid habitats across western North America, from southwestern Canada through the western United States into Mexico, generally favouring rocky or sandy ground that provides both daytime shelter and effective camouflage.