Lycodon—4 species of wolf snakes in northern Thailand
The genus Lycodon (wolf snakes)
Wolf snakes are small to medium-sized snakes, distinguishing themselves by their dentition: the anterior teeth of their upper jaw are enlarged, but they are not venomous fangs. These characteristics have given rise to the genetic name ‘wolf snakes’, which, as Tweedie (1) remarks, is rather unfortunate, as it suggests ferocious and formidable qualities which these harmless, non-venomous and mild-mannered little snakes certainly do not possess.
They are oviparous, and in general the females lay no more than ten eggs per clutch. Their diet consists predominantly of skinks, geckos and frogs which they prey upon during the night.
David and co-authors (2) listed six species occurring in Thailand. Four of them are found in the North. One of them, the Laotian Wolf Snake (Lycodon laoensis) belongs to the most common snakes of the region—actually it is more common than the Common Wolf Snake (Lycodon capucinus). In some species, the colouration and pattern of the juvenile differs considerably from the adult’s.
Most wolf snakes are nocturnal and the rather small eyes have a vertically oval pupil—however, this is difficult to see as both iris and pupil are black.
Wolf snakes, as well as the members of the related genera Dinodon and Dryocalamus, are called ngu plong in Thai, which means ‘banded snake’, as many have a banded pattern, at least when they are young.
Common Wolf Snake (Lycodon capucinus)
This snake is also known as the House Snake.
Thai name: ngu plong chanuan soi luang – งูปล้องฉนวนสร้อยเหลือง
This wolf snake can reach a length of 60 cm. The back is purplish brown and many dorsal scales have light yellow edges forming a fine reticulum.
Behind the brown head is an inconspicuous yellowish collar. Soi luang in the Thai name refers to this ‘yellow neckband’. The belly is uniformly white.
This species is mostly found in deciduous forests and cultivated land at elevations below 700 metres. The name House Snake is appropriate as it often enters houses to hunt geckos. However, most snakes live far from human habitation.
It occurs in much of Southeast Asia and is rather common throughout Thailand, including the north. Tweedie supposed this is the most frequently encountered snake in peninsular Malaysia due to its habit of entering houses. (3)
Banded (Mountain) Wolf Snake (Lycodon fasciatus)
Thai name: ngu plong chanuan muang nua – งูปล้องฉนวนเมืองเหนือ
This handsome snake is quite common in the northern mountains at elevations of over 700 metres.
It reaches a length of 80 cm. It is black with many light crossbars with fuzzy edges. These crossbars seem to be pinkish as a result of light brown pigment accumulated in many of the white dorsal scales.
Anteriorly the black crossbars extend and encircle the white belly, 3-5 successive ventral scales being entirely black, separated by completely white crossbars four ventral scales wide.
Posteriorly the ventral crossbars become less conspicuous, most ventral scales containing much black pigments.
The subcaudals are completely black. The dorsal scales are smooth, the ventral scales rather shiny.
The juveniles resemble the adults. Superficially, it resembles the Malayan Banded Wolf Snake (Lycodon subcinctus), but in the latter the belly is completely white, while the dorsal crossbars are not fuzzy, while in adults these have disappeared completely in the posterior half of the body.
Another difference is the shape of the hemipenis: smooth in the Malayan Banded Wolf Snake and covered with spines in the Banded Mountain Wolf Snake.
This mountain snake is more slender than the deadly Blue Krait (Bungarus candidus). The latter has much enlarged vertebral scales, while in no species of wolf snakes the vertebrals are enlarged. Except for some vague greyish spots, the belly of the blue krait is completely white, very different from the belly of this species of wolf snake.
The anal shield of the banded mountain wolf snake is single.
In contrast to the other Lycodon-species occurring in Northern Thailand, the banded mountain wolf snake is often active during the day.
It is widespread in the region. I came across it in Chiang Mai, Lampang, Mae Hong Son, Phitsanulok and Tak, and in Loei in the adjacent northeastern region.
In Thailand its distribution is probably restricted to the north and adjacent areas of the northeast, and in Thai this snake is therefore called ‘banded snake from the northern country’.
Laotian Wolf Snake (Lycodon laoensis)
Thai name: ngu plong chanuan lai luang – งูปล้องฉนวนลายเหลือง
This handsome little snake is widespread in northern Thailand and is common in the lowlands and in the hills at low elevations and, including agricultural lands, orchards and gardens, and deciduous forests, where it is usually hidden in the litter or under debris.
It reaches a length of 50 cm, the slightly distinct head with small black eyes being dorsoventrally compressed. The brownish black dorsum is adorned with well-developed, bright yellow crossbands which are about one third the width of the black bands separating them. Posteriorly, these crossbands are narrow and bifurcate laterally, which may give the impression of a reticulum. At the back of the brown head is a well developed nape band. The dorsal scales are smooth and have a purplish lustre. The belly is uniformly white.
This snake is mainly terrestrial and active during the night when it preys on lizards, in particular skinks, and frogs. It is a harmless, mild-mannered snake, but may be mistaken for a juvenile banded krait, a deadly venomous snake. In the latter, the yellow and black bands are of almost equal in size all over its length, and encircle encircle the body. The Banded Krait further distinguishes itself by the pronounced vertebral ridge and much enlarged vertebral scales—both absent in the Laotian Wolf Snake.
It is common throughout Thailand, including the south, and occurs in most of mainland Southeast Asia.
Malayan Banded Wolf Snake (Lycodon subcinctus)
Thai name: ngu plong chanuan ban – งูปล้องฉนวนบ้าน
This is the largest of the wolf snakes occurring in the northern region, reaching a length of over one metre. The black and white banded juveniles have up to 20 white crossbars, which are about half to one third the size of the black bands in between.
As they mature, the white bands disappear gradually when the white dorsal scales are filled up with black pigment from the centre of the scale.
In adults the posterior half of the body is uniformly black, whereas anteriorly 4 or 5 ‘white’ bands can still be distinguished of which the white scales have a black centre. The dorsal scales are smooth. The belly is uniformly white.
This snake is found in both deciduous, evergreen and mixed forests and in cultivated land, often near human settlements, which have given rise to the Thai name ngu plong chanuan ban, which means ‘banded snake from the house’. It is common throughout Thailand and occurs in much of Southeast Asia.
The Malayan banded wolf snake may be confused with the deadly venomous Blue Krait (Bungarus candidus), but adults of the latter are banded from their head to the tip of their tail, while their vertebral scales are much enlarged.
©SJON HAUSER: TEXT AND PICTURES
(1) Tweedie, M. W. F., 1953. The Snakes of Malaya. Gouvernment Printing Office, Singapore: 59.
(2) David, Patrick, Merel J. Cox, Oliver S. G. Pauwels, Lawan Chanhome, and Kumthorn Thirakhup, 2004. Book Review. When a book review is not sufficient to say all: an in-depth analysis of a recent book on the snakes of Thailand, with an updated checklist of the snakes of the Kingdom. The Natural History Journal of Chulalongkorn University 4(1): 47-80, April 2004: p. 72.
(3) Tweedie, ibid: 60.