How to Identify the Tonkin Pit Viper (Identification Guide)
A green arboreal pit viper native to the Tonkin region of northern Vietnam, sharing classic Asian pit viper features with subtle local variation.
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Key identifying features
The Tonkin Pit Viper is another member of the extensive Asian green pit viper radiation, exhibiting the group's defining traits: a broad triangular head clearly set off from the neck, heat-sensing facial pits, and vertical pupils, paired with a slim, prehensile-tailed body built for life among branches and leaves.
Coloration & pattern
The body is generally a bright to medium green, which helps the snake blend into foliage. As in many related species, a thin pale stripe, often white or yellowish, may run along the lower side of the body, sometimes more developed in males. The tail may show a reddish-brown tinge toward the tip in some individuals. The belly is typically pale green or yellow-green.
Head, eyes & scales
The head is wide and triangular, distinctly broader than the neck, housing the venom glands typical of pit vipers. A heat-sensing pit lies between the eye and nostril on each side of the face. Eyes are moderately large with vertical pupils, a key visual cue separating pit vipers from round-pupiled harmless green snakes. The dorsal scales are keeled, giving the body a slightly textured rather than glossy appearance.
Size & body shape
Adults of this species are typically small to medium in size, often falling in the 50 to 85 centimeter range for total length. The body is slender and laterally compressed, an adaptation for climbing, and the tail is prehensile, aiding grip on branches and vines.
Range & habitat where you'll see it
This species is associated with the Tonkin region of northern Vietnam, an area of hill and montane forest. It favors forested habitats, particularly near streams, trails, and forest edges, and is primarily nocturnal and arboreal, most often encountered at night coiled on low vegetation or branches.
How to tell it apart from look-alikes
As with most green pit vipers in the region, distinguishing this species from close relatives by color pattern alone is unreliable, since many share a similar green body with pale lateral striping and a reddish tail tip. Locality within northern Vietnam and closer examination of scale characteristics are typically needed for confident species-level identification. Nonetheless, the combination of triangular head, vertical pupils, heat-sensing pits, and keeled scales clearly marks any individual as a pit viper rather than a harmless green snake, which lacks these features and usually has a more slender head and smoother scales.
Frequently asked questions
Is the Tonkin Pit Viper venomous?
Yes, it is a venomous pit viper, and this guide focuses solely on visual identification.
What does the Tonkin Pit Viper look like?
It is green-bodied with a triangular head, vertical pupils, and often a pale lateral stripe and reddish tail tip.
Where does it live?
It is found in forested hill and montane habitats in the Tonkin region of northern Vietnam.
How can I tell it apart from a harmless green snake?
Check for a triangular head, vertical pupils, heat-sensing pits, and keeled scales, all absent in harmless green snakes.
Is it active during the day?
No, it is mainly nocturnal, typically encountered resting on vegetation at night.