Colubridae-2-D-G-Check list snakes northern Thailand

Colubridae-2-D-G-Check list snakes northern Thailand: snake species in the genera Dendrelaphis, Dinodon, Dryocalamus, Dryophiops, Gongylosoma and Gonyosoma.

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Dendrelaphis cyanochloris, the Blue Bronzeback (pictures above). Slender snake with conspicuous broad black postocular streak that peters out on the neck. When the anterior part of the body is expanded a multitude of bright glitters are seen (the edges of the dorsal scales) often forming vague oblique reticulations. The upper side of the head and the dorsum is brown to copper brown, the belly pale green (pale yellow anteriorly, as the chin and throat)). It is rather common in most of northern Thailand’s forests at elevations of 700-1400 m asl. A. Head of juvenile from Umphang District, Tak. B. Adult from Pang Sila Thong District, Kamphaeng Phet. C. Belly shown by DOR from Doi Inthanon, Mae Chaem District, Chiang Mai. D. Upper side head of adult from Pai District, Mae Hong Son. E. Juvenile from Phu Hin Rong Kla National Park, Nakhon Thai District, Phitsanulok.

Dendrelaphis ngansonensis, the Vietnamese Bronzeback (pictures above). This bronzeback is very similar to D. cyanochloris, but it can be told apart  by its cream belly (pale green in D. cyanochloris). What’s more, the first row of dorsals is cream like the belly (bronze-brown in D. cyanochloris) (see D). This bronzeback can easily reach a length of 150 cm, and is therefore much larger than D. cyaonochloris (max. lenght 133 cm). It is known from the Central Thailand (Chanthaburi, Nakhon Nayok) and Northeast Thailand (Nakhon Ratchasima, Chaiyaphum), but I also came across it in Nam Nao District, Phetchabun, in the northern region. A-D. All pictures are of the same road-killed subadult from the Khao Yai National Park (Mueang District, Nakhon Nayok).

Dendrelaphis nigroserratus or Saw-tooth-necked Bronzeback (pictures above). This species was first described in 2012. Its meristics are similar to D. cyanochloris but it grows larger in size (the largest specimen thus far recorded was 163 cm). The conspicuous black saw-tooth pattern on the neck easily tells it apart from the other bronzeback species. The upper side of the head is greenish bronze (not brown as in D. cyanochloris). In northern Thailand it is recorded only in the southern part of Tak Province (Umphang and Phop Phra Districts) where it lives in forests at elevation of 800-1300 m asl., often hiding in bamboo clubs. A. Subadult from Umphang District, Tak. B. Juvenile from Umphang District, Tak. C. Head of an adult from Phop Phra District , Tak. D. Adult from Kaeng Krachan National Park, Kaeng Krachan District, Phetchaburi (Central Thailand).

Dendrelaphis pictus, the Common Bronzeback (pictures above). The upper side of this slender snake (maximal length 130 cm) is bronze, the belly whitish or pale yellow. The head is copper brown. It can be told apart from the other bronzeback species in Thailand by a distinct black ventrolateral stripe that runs over the corners of the ventral shields (B). When the snake expanses the anterior part of the body, the glittering, bright blue edges of the scales are shown (D, F). It is a very common snake throughout Thailand, including the northern region. It is a diurnal species, most often encountered in deciduous forest, plantations and gardens at low elevations (100-600 m asl). A. An adult from Mae On District, Chiang Mai. B. View of flanks and belly of a road-killed specimen from Lampang’s Mueang District, showing the black ventrolateral stripe (blue arrow) and the ventral keels (red arrow). C, F. Individual from Lampang Province. D. Juvenile from Chiang Mai’s Mae On District. E. An adult from Phayao’s Mueang District.

Dendrelaphis subocularis or the Subocular Bronzeback. This bronzeback is also known as Mountain Bronzeback, a bit misleading name, at least in northern Thailand where it is usually found in low hills, often the same habitat where D. pictus thrives. It superficially resembles D. pictus but there are many differences. First, there is no black ventrolateral stripe, but a pale brown one (A, B, G). Second, the 5th supralabial is large and cup-shaped and the eye rests on this characteristic “subocular” shield. (D, E, F, J). Third, there is a pale vertebral stripe from the back of the head (E, H) that peters out 2-3 head lengths behind the head. Another characteristic of the coloration is that the middle part of the dorsum is reddish brown in contrast to the greenish-bronze color of the remaining parts of the dorsum. Moreover, the tongue is black (H) versus bright red in D. pictus and all other bronzebacks known from northern Thailand. As in most other bronzebacks, the glittering, bright blue edges of the scales are shown, when the anterior body is expanded. The snake is widely distributed in northern Thailand but less common than D. pictus. A-B: Adult from Mae On District, Chiang Mai. C. Dorsal skin of a specimen from Mae La Noi District, Mae Hong Son, D. Morph with yellow throat from Wang Nuea District, Lampang. E. An adult from Pong District, Phayao, showing the reddish brown color at the middle of the dorsum. F-G. An adult from Chiang Mai’s Mae On District. H, I, J. Specimens from Phayao’s Pong District. (Hemipenes in picture I similar to those of D. pictus, D. cyanochloris and D. nigroserratus.)

Dinodon septentrionalis. This black-and-white wolf snake  reaches a length of over one meter. There are about 35-40 white bands on the body, tail included, which are one third or less of the length of the black ‘bands’. The dorsal scales are smooth. This snake looks strikingly similar to the dangerous kraits Bungarus candidus and B. wanghaotingi. But in fact there are many differences. In D. septentrionalis the vertebral scales are NOT enlarged (A); the black bands often continue on the belly (C), in particular posteriorly; and the subcaudals are divided (in pairs). Their head scalations also show differences. In juveniles part of the upperside of the head is white. This snake is widespread in the region in evergreen forest at an elevation of 1200-1800 m.
A. A subadult from Nakhon Thai District, Phitsanulok. B. An adult from Phop Phra District, Tak. C. Details of the belly of a specimen from Pua District, Nan.

Dryocalamus davisonii, Blanford’s Bridle Snake (above) is a very slender, black snake with about 50 white bands on the body and tail, which can reach a length of about 100 cm. The white bands in the posterior half are usually “dirty” due to the numerous grey pigment grains deposited. It is a rare snake in northern Thailand. Though it is widespread, its occurrence is probably restricted to a number of relatively small populations in deciduous hill forest. In Northeast, Central and South Thailand this snake appears to be (much) more common. In South Thailand and southwestern Central Thailand, it is sympatric with the similar Dryocalamus subannularis which has a more brownish ground color and more yellowish-colored bands. What’s more, D. subannularis has a preocular (absent in D. davisonii) and 15 rows of dorsal scales (13 in D. davisonii) but these characters are usually not clear in most pictures, so morphs and/or old specimens of D. davisonii with quite ‘dirty bands’ can be confused with D. subannularis. Identification of D. davisonii is possibly also complicated as a new species may be involved that has not yet been described in a scientific journal. A member of a research team from Sakaerat, southern Northeast Thailand, had posted a picture of a snake on Facebook that looks very similar to D. davisonii with moderately ‘dirty’ bands and claimed it to be a (new) species different from both D. davisonii and D. subannularis. However, details on its scalation were not revealed (I thank Ton Smits for sharing this information on the internet with me!) So it is possible that some of the specimens in the pictures above in fact belong to the new, not yet described cryptic species. However, so far I identify them as truely D. davisonii. A-B. A juvenile from Pak Chong, Nakhon Ratchasima Province, Northeast Thailand. C-E. An adult, 70 cm long DOR from Chiang Muan District, Phayao. F. A specimen from Ko Chang District, Trat, southeastern Central Thailand. G-H. An individual from Ko Phi Phi Island, Krabi, South Thailand. Thanks to Johan van Rooijen and Jacob Ohlin for pictures F, respectively G and H !!

Dryophiops rubescens, the Red Whip Snake. This whip snake is probably quite widespread in Thailand, but it is rarely seen. Body shape is quite similar to the Oriental Whip Snake Ahaetulla prasina (A, C) , but the head is not so long and pointed (B), and it grows no longer than 80 cm. The body is pale brown with reddish-brown, the belly pale greyish-brown. There is a mask-like pattern on the upper side of the head. In northern Thailand I only came across it in Tak Province (Umphang, Phop Phra and Tha Song Yang districts) in forested areas above 800 m. I also came across the species in Khao Yai N.P. (Pak Chong District, Nakhon Ratchasima Province). In the Central Region it is also known from Kaeng Krachan N. P. (Phetchaburi) and Khao Ang Ruea Nai W.S. (Chonburi/Chachoengsao Prov.), but the species is best known from the South. A. A specimen from Bohol, the Philippines. B. Upper side of head and neck of a specimen from Phop Phra District, Tak. C. A DOR dried by exposure to sunlight from Tha Song Yang District, Tak.
Gongylosoma scripta (above). This ground snake is uncommon in northern Thailand, only found in the mountains of Tak and Kamphaeng Phet Province. It is a brown snake of small size (up to 55 cm). A. Juvenile from Umphang Wildlife Sanctuary, Umphang District, Tak. B. Adult from Mae Wong National Park, Khlong Lan District, Kamphaeng Phet. C. Head of an adult from Umphang District, Tak. D. Head and neck from an adult specimen, Khao Yai National Park, Nakhon Nayok Province (Central-Thailand).
Gonyosoma oxycephalum, the Red-tailed Rat Snake (above). Large green snake reaching a length of 240 cm. Body green, tail pale reddish-brown. Dark, rather vague streak runs from the tip of the snout through the eye to the end of the upper jaw (B). Tongue metallic blue. Widespread in the region where it prefers forests at an elevation of 500-800m asl. A-B. Adult from Tha Song Yang District, Tak. C. Subadult from Mueang Pan District., Lampang.
Gonyosoma prasinum, the Green Tree Racer (above). Max. length about 100 cm. Both males and females have a white ventrolateral stripe. Rather common snake throughout the northern region in evergreen forest at elevations >1000 m asl. A. Adult from Doi Saket District, Chiang Mai. B. Head and neck of a juvenile from Umphang District, Tak. C. A juvenile from Bo Kluea District, Nan.