A cute little snake
Yesterday night I crashed at the laboratory, so visiting the bathroom demanded a nightly walk. At 01.51 a.m. I made Dokmai Garden’s second sighting of the white-spotted slug snake (Pareas margaritophorus, Colubridae, subfamily Pareatinae).
It was motionless in spite of vibrations from my walking feet. It did not seem wounded though, and being a totally harmless species, I gently poked it with a stick and it raised its head to see what was going on. I poked it again and its tongue flickered to analyze the gas composition of the surrounding air. It decided the smell was not appealing and so it vanished before my eyes, seemingly diving into the underground. I figured there was a cricket hole under the grass.
This beautiful specimen was about 30 cm, and such slug snakes never grow larger than half a meter. It is native to the tropical monsoon areas of India and Southeast Asia, not found in rain forests. The literature claim it prefers evergreen forests, while Dokmai Garden is situated in a dry deciduous forest area. That statement is due to a confusion of two species:
Update on May 4th, 2013:
There are two distinct but similar looking species, both widespread and common in northern Thailand. In Pareas margaritophorus all dorsal scales are completely smooth (see top picture), whereas the scales of the median rows in Pareas macularius are weakly keeled. There are many other differences such as shape and colour of the collar but these are less absolute than the keeling.
Interestingly, in northern Thailand Pareas margaritophorus lives in lowlands and hills up to an elevation of 900m (usually below 700m), while Pareas macularius is found at elevations of 750 to 1700m, often evergreen forests. There is very little or no overlap of the habitats they prefer.
The confusion about the synonymy is due to a Chinese article which appeared in the Sichuan Journal of Zoology, written by Huang (2004). In this article the synonymy of Pareas macularius (the supposed junior) and Pareas margaritophorus was proposed. It was based on incomplete data, and without examining the holotypes (the original specimens on which species descriptions are based). However, the synonymy was accepted by a number of other Chinese authors, including those of articles in well-respected journals such as Zootaxa. Thus, P. macularius was gradually exterminated, at least on paper. At last, but only recently, this synonymy was also adopted in the species list of the Reptile-Data Base.
According to Sjon Hauser who provided data for this update, P. macularius is alive and well as a distinct species. It’s probably this region’s most common mountain snake at elevations above 1000 m. Sjon Hauser and Gernot Vogel are working on a paper to refute Huang’s synonymy and to resurrect P. macularius as a distinct species.
An interesting feature of all slug snakes is the set of bent teeth facing backwards, enabling them to scoop out snails from their shells. Some slug snakes are so well adapted to snail consumption that they have assymetric jaws, adapted to feeding on clockwise-coiled shells.
While the stern eagle-like look of a viper signals danger, a slug snake looks cute with its blunt head and large round eyes.