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 asymmetric
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.
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 claims
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:
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 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
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.