Natricidae-Illustrated check list snakes northern Thailand

Natricidae, the family of Keelback Water Snakes

Some 15 species of this family are known to occur in Thailand’s northern region. In most species the dorsal scales are distinctly keeled. Most are small- or medium-sized.

Amphiesma stolatum, the Striped Keelback (pictures above). Dark brown snake that reaches a length of 70 cm with a pair of light buff stripes that extend from the neck to the end of the tail. Anteriorly, a row of blackish, squarish blotches between the stripes. Upper side of the head slate or ashy grey. The belly is white. Occasionally specimens with a yellow throat and chin, and bronze head, are seen (A). The dorsal scales are strongly keeled. When the anterior body is a little expanded, it shows a reticulated pattern (B). This snake is locally common in the northern region. A. An adult from an longan orchard in Lamphun’s Li District. B-C. Adult specimens, both from Mae Rim District, Chiang Mai.
More about this species (in Dutch), click here .

Hebius bitaeniatum, the Two-striped Water Keelback. This brown snake reaches a length of 70 cm. Body scales are strongly keeled in all rows (C). A conspicuous pair of light brown lateral stripes extends from behinds the head (A) to the tail (B) . The belly is yellow, but the corners of the ventral scales are orange brown (D). A pair of dotted stripes extends overt the belly (D). A-B. An adult male specimen from Doi Inthanon, Mae Wang District, Chiang Mai. C-D. A specimen from Doi Inthanon, Mae Chaem District, Chiang Mai.

Hebius deschauenseei, the Northern Keelback, living in and neat mountain streams throughout the region, It is a slender brown snake snake with a long tail. The belly pattern in quite  variable. In most of the region there are 3 rows of dark spots (E) that get larger and darker when the individual matures (F). However, in southern Tak Province the specimens have only 2 rows of brown spots near the corners of the ventral shield while most of the belly remains white even in old individuals. It is possibly a local bariation, as otherwise the snakes from Tak do not seen to differ from the snakes from the rest of the region. A-C. Subadult from Doi Suthep, Mueang District, Chiang Mai. D & H. Juveniles from Doi Suthep E. Belly pattern of subadult from Doi Suthep. F. Belly pattern of adult from Pua District, Nan. G. Belly pattern of adult from Umphang District, Tak.

Hebius khasiense, the Khasi Hills Keelback. This slender, brown snake reaches a length of 60 cm. The characteristic white blotches on the supralabials (B-C) and the row of squarish, dark brown blotches on the corners of the white ventral shields (C) tell this species apart from the congeneric H. deschauenseei. It occurs throughout northern Thailand’s mountain forests at elevations above 1000 m asl, usually close to streams or pools. Locally it may be rather common (e.g. in Phu Hin Rong Kla National Park, Phetchabun).
A-B. Individual from Umphang District, Tak. C. A juvenile from Phu Hin Rong Kla National Park, Nakhon Thai District, Phitsanulok. D. An adult from Chiang Mai’s Mae Taeng District, showing the slender shape of the body. E. A juvcenile from Doi Surhep, Mueang, Chiang Mai.

Opisthotropis spenceri, Spencer’s Stream Snake (above)  is a light brown snake with a cream belly, measuring up to about 70 cm. It is a rare, aquatic snake that was first described in 1918, and until recently  only known from two specimens from “Muang Ngaw”, which nowadays refers to Lampang’s Ngao District. In 2011, it was ‘rediscovered’ in Tha Wang Pha District, Nan, and a year later I came across it in Doi Saket and Mae On Districts in Chiang Mai Province. All records were from mountain streams. A. DOR-specimen found 10 m from a stream in Doi Saket District. B & C: details of the same individual.

Paratapinophis praemaxillaris, Angel’s Stream Snake (not depicted). A brown stream snake with indistinct pale brown reticulations on the flanks.  All dorsal rows are smooth. Body shape resembles Xenochrophis picator, but tail shorter. In Thailand this rare snake has been known from a single record from Doi Saket, Chiang Mai, but recently it was rediscovered  in Nan Province.
Psammodynastes pulverulentus, the Mock Viper (above). This little snake (max. 50 cm) is widespread and common throughout the mountains of northern Thailand, but it can also be found at low elevations in the hills and valleys. The coloration varies from dark brown to light ocher and pale buff. Belly anteriorly yellow, with rows of brown dots. A-B. Dark-colored specimen from Mueang Pan District, Lampang. C. Light-colored individual from Doi Saket District, Chiang Mai. D. An individual from Umphang District, Tak.

Rhabdophis chrysargos, the Speckle-bellied Keelback (above) can reach a length of 80 cm. It is uncommon in northern Thailand. I only came across this species in mountain forests in Tak Province. The northern district of Tha Song Yang is probably the most northern locality in its range. A. A juvenile from Umphang District, Tak. B. An adult from Umphang District, Tak. C-D. Lateral view and upper side of the head of an adult specimen from Tha Song Yang District, Tak.

Rhabdophis nigrocinctus, the Green Keelback (above) may reach a length of 100 cm. It is widespread in the northern region, where it is often common near streams and waterfalls in forested mountains at 500-1500 m a.s.l. A. An adult from Doi Suthep National Park, Mueang District, Chiang Mai. B. An adult luring from a gap between rocks in the bedding of Mae Koeng Waterfall, Wiang Kosai National Park, Wang Chin District, Phrae. C. Head of an adult from Doi Suthep National Park, Mueang District, Chiang Mai. D. A juvenile on a mountain road in Mae Wang District, Chiang Mai.

Rhabdophis subminiatus, the Red-necked Keelback can reach a length of more than 100 cm. It  is widespread and common in lowlands and (forested) hills of the North. It also occurs at high elevations (1000-1700 m a.s.l.) in mountain forests. In the specimens living at high elevations the ground color of the body is usually olive green (vs brownish in the lowland and low hills) and probably belong to the subspecies Rhabdophis subminiatus helleri. A. An adult, Mueang Lampang. B. An adult from Hot District, Chiang Mai. C. Head of an adult individual from Ban Khok District, Uttaradit. D. Head of a juvenile from Samoeng District, Chiang Mai. E. A specimen from Doi Ang Khang, Fang District, Chiang Mai, devouring a toad (Thanks to ‘Nature Lovers’ from Chiang Mai for this nice picture!!)

Sinonatrix percarinata, the Chinese Keelback (not depicted here) resembles the Yunnanese Keelback, the crossbars, however, being Y-shaped on the flanks. It has been reported from the northern region (Chiang Mai and Tak Provinces), but I have doubts about the validity of these records.
Sinonatrix yunnanensis, the Yunnanese Keelback (above). A rare snake, known from just a few mountain localities at high elevations. Pinkish to brick red with black crossbars that form an “X” on the flanks. The legs of the X strech far onto the white belly. In olders specimens the brick red color turns dark brown or dark grey making the crossbars less conspicuous. A. A subadult from Mueang Pan District, Lampang. B-C. A juvenile from Pai District, Mae Hong Son.
Xenochrophis flavipunctatus, the Yellow-spotted Keelback (above). This keelback water snake can reach a length of about 100 cm. Most rows of dorsal scales strongly keeled. It resembles the Checkered Keelback (X. piscator) but has a distinct funnel-shaped mark on the neck, the apex pointing backwards. What’s more, the ventral shields have distinct black edges over their entire width (in X. piscator only in the corners). The snake is often quite colorful, with yellow throat and supralabials, or series of red dots on the flanks. It can be very common in the ditches, swamps and pools of the northern valleys, where it is often syntopic with X. piscator. It seems to be absent in the most western parts of the region (Mae Hong Son and western Tak Province). A. An adult ‘yellow morph’ from San Kamphaeng District, Chiang Mai. B. A yellow morph from Phran Kratai District, Kamphaeng Phet. C. An adult from Mueang, Chiang Mai. D. A red-spotted morph from Chiang Dao District, Chiang Mai. E. A juvenile, red-spotted morph from Mueang, Tak.

Xenochrophis piscator, the Checkered Keelback (above). This species of keelback water snake can reach a length of 120 cm. Most rows of dorsal scales strongly keeled. It is less colorful than the Yellow-spotted Keelback (X. flavipunctatus), never showing red spots on the flanks or a distinct yellow throat. A neck mark and postocular streaks are usually vague, and the edges of the ventral shields are only black in the corners. Some specimens (B) have a distinct checkered pattern on the anterior body. The upper side of the head is often greenish brown (C). This snake is widespread and common throughout northern Thailand, in particular in and near streams, ditches and pools in the valleys, but it can also be found at elevations as high as 1200 m asl. A. An individual from Mae Hong Son’s Mae Sariang District. B. A specimen from Chiang Mai’s Mueang District, showing a distinct checkered pattern. C. From Tak’s Mae Ramat District. D. Head of a very large individual (121 cm) from Mueang Chiang Mai with vague postocular streaks. E. Specimen from Chiang Mai’s Doi Saket District.
Xenochrophis punctulatus or Spotted Keelback Water Snake (not depicted). Dorsum brown with whitish small spots. Ventral shields and the dorsal scales in the first two rows have black edges. Median rows are weakly keeled. A first report for Thailand in 2001 was from Mae Hong Son Province but I have some doubts about the validity of the locality of this record. Later (undoubtful) records were from Ranong Province in South Thailand.