Amphiesma bitaeniatum, a rare mountain snake
Two-striped Keelback (Amphiesma bitaeniatum)
Thai name: ngu lai sap song khit – งูลายสาบสองขีด
This little dark brown snake has a pair of light brown dorsolateral stripes running from the neck to the tip of the tail. The stripes are edged on both sides by a narrow black line. The snake is strongly keeled above, only the scales of the most lateral rows (rows 1 and 19 at midbody) are not keeled. The dorsals are deeply notched posteriorly.(1)
The belly is yellowish-cream, becoming orange brown in the lateral corners of the ventral scales. Also laterally, on the outer edges of the ventral scales, is an irregular, amoeboid-shaped dark dot. This snake can reach a length of 70 cm. The specimen in the pictures above had 162 ventral scales.
The tail is rather long, about 30-31 per cent of the total body length.
The head is distinct from the neck, the supralabials are white with black fissures.
There are about 20 teeth in the upper jaw, mostly curved and hooked and gradually increasing in size from the front to the rear. The last tooth in the rear is distinctly enlarged (see picture below, right). This snake has quite large, black eyes with a round pupil.
This is a rare mountain snake. A picture of a specimen from Thailand was first published in 1999. The photograph was taken by Klaus-Dieter Schulz at high elevation (1800 m. a.s.l.) in ‘primary rainforest’ on Doi Inthanon, northern Thailand.
The snake was spotted in the late afternoon near a stream. (2)
A few years ago, a photograph of a living specimen taken by Montri Sumontha was posted on a website.
Little is known of the habits of this snake, but it is supposed to be mainly diurnal and terrestrial.
I only came across this species a few times, in all cases as DORs (Dead on Road) in Doi Inthanon National Park in Chiang Mai (Mae Wang and Mae Chaem districts), where seems to be restricted to montane and wet evergreen forest at high elevations of about 1600-1900 m a.s.l.
It has also been recorded in Yunnan (southern China), northern Myanmar, Laos and northern Vietnam. Doi Inthanon is the most southern location where this species is known to occur. (3)
(1) Patrick David, Gernot Vogel & Olivier S. G. Pauwels, 2005. The occurrence of Amphiesma bitaeniatum (Wall, 1925) in Vietnam, with preliminary remarks on the group of Amphiesma parallelum (Boulenger, 1890) (Serpentes, Colubridae, Natricinae). Salamandra, 41 (20 November 2005): 167-178 (p. 172).
(2) T. Chan-ard, W. Grossmann, A. Gumprecht and K.-D. Schulz, 1999. Amphibians and Reptiles of Peninsular Malaysia and Thailand. An illustrated checklist. Amphibien und Reptilen der Halbinsel Malaysia und Thailands. Eine illustrierte Checkliste. Bushmaster Publ., Würselen: 1-240.
(3) David et al., ibid.; Indraneil Das, 2010. A Field Guide to the Reptiles of Thailand and South-East Asia. Asia Books, Bangkok: 330-331.