Rhadinophis prasinus, the little known Green Tree Racer

young green tree racer

A juvenile specimen from Umphang district, Tak province.

Genus Rhadinophis

This genus consists of two species (Rhadinophis frenatus and R. prasinus), formerly grouped in the large genus Elaphe.

Based on molecular data (mtDNA) they were regrouped in the genus Gonyosoma (1), a relationship that was already proposed by Günther in 1864.

More recent research justified the creation of the new genus Rhadinophis for the two.
Both species are known from northeastern India, southern China and northern parts of mainland Southeast Asia.

One of them (R. prasinus) is known from Northern Thailand, where it occurs widely.

Green Tree Racer (Rhadinophis prasinus)

This snake is also known as Green Trinket Snake.

This bright green, little-known, medium-sized snake reaches a length of just over one metre.
The dorsal scales are smooth or faintly keeled, some of them have a white edge. The skin between the scales is black and is exposed when the body is somewhat expanded.

The distal end of the tail is olive or brownish bronze, but near the vent the tail is as green as the rest of the body.

The throat is white, the keeled ventral scales are creamish anteriorly and progressively darker (pale green) posteriorly, the lateral corners being white.

specimen from Chiang Mai

A green tree racer from Doi Saket district, Chiang Mai.

same specimen

The same specimen in a defensive posture.

The head is distinct from the neck, the snout is rounded. The fissures of the head scales are black in juveniles.

The medium-sized eye has a round, black pupil. The iris is greenish. There is a faint postocular stripe. The tongue is greyish brown.

This snake is not uncommon in Northern Thailand’s evergreen forests at elevations of 900 – 1500 metres a.s.l. It is active during the day and is an excellent climber due to the well-developed ventral keels. It seems to prefer low trees and bushes, but often ventures on the ground. Young animals may stick to woody vegetation and resemble the vines of creepers.

It is known to hunt small mammals which it kills by constriction.

In a number of works on Thailand’s snakes this species has been neglected. It is not mentioned in Taylor’s elaborate Thailand-study from 1965 (2), and is also absent in Merel Cox’s The snakes of Thailand and their husbandry (3) and Piboon Jintakune’s Ngu phit nai prathet thai (4).

In the popular Photographic Guide to Snakes and other Reptiles of Thailand and South-east Asia (5) it got the attention it deserves, being described as the green tree racer Elaphe prasina.

An adult from Doi Ang Khang, Fang district, Chiang Mai province.

An adult from Doi Ang Khang, Fang district, Chiang Mai province.

Doi Inthanon juvenile

A juvenile from Doi Inthanon National Park, Mae Wang district, Chiang Mai province.

In Lai ngu thai / Snakes in Thailand by Wirot Nutphan (6) its binomen is Gonyosoma prasina, while icons indicate that the author believes it to be a very rare snake, occurring only in Thailand’s Northeastern region.

In a review article by David and others (2004) the binomen had been changed according to the rules of Latin grammar into Gonyosoma prasinum. (7)

At last, in the recent Field Guide to the Reptiles of Thailand and South-east Asia it got its new binomial name, Rhadinophis prasinus, while Green Trinket Snake is its English name. (8)

Beside its affinity to the congeneric Khasi Hills Trinket Snake (Rhadinophis frenatus), the species might be closely related to the spectacular Vietnamese Horned Snake (Rhynchophis boulengeri).

Striking similarities between R. frenatus and the latter, such as the fusion of the loreal with the prefrontal, have been reported as early as 1999. (9)

This species superficially resembles the Red-tailed Rat Snake (Gonyosoma oxycephalum), but there are a number of obvious differences:

map distribution

Localities in Northern Thailand where I came across the Green Tree Racer.

The Red-tailed Rat Snake is considerably larger, has a conspicuous postocular strike and a metallic blue tongue, while its tail is rusty or reddish from the vent to the tip.

Locally, the Green Tree Racers can be rather common.

I came across them on Doi Suthep, Doi Inthanon and Doi Ang Khang in Chiang Mai province, and in the mountainous areas of  Mae Hong Son, Chiang Rai, Lampang, Tak and Nan provinces, areas covering most of mountainous Northern Thailand. (10)

©SJON HAUSER: text and pictures

Notes:

(1) Urs Utiger, Beat Schätti and Notker Helfenberger, 2005. The oriental Colubrine genus Coelognathus Fitzinger, 1843, and classification of Old and New World ratsnakes (Reptilia, Squamata, Colubridae, Colubrinae). Russian Journal of Herpetology, 12 (1): 39-60.

(2) Edward H. Taylor, 1965. The serpents of Thailand and adjacent waters. The University of Kansas Science Bulletin, vol. 45 (No. 9), 609-1079.

(3) Merel J. Cox, 1991. The Snakes of Thailand and their Husbandry. Krieger, Malabar, Florida.

(4) Paibun Jintakune, 2000. Ngu phit nai prathet thai [Venomous snakes in Thailand]. Tichon, Bangkok [in Thai].

(5) Merel J. Cox, Peter Paul van Dijk, Jarujin Nabhitabhata, and Kumthorn Thirakhupt, 1998. A Photographic Guide to Snakes and other Reptiles of Thailand and South-East Asia. Asia Books, Bangkok: 53. It got a similar fair treatment in Indraneil Das, 2002. A Photographic Guide to Snakes and other Reptiles of India. New Holland publishers, London: 33.

Umphang juvenile

Umphang juvenile.

(6) Wirot Nutphan, 2001. Lai ngu thai /Snakes in Thailand. Amarin, Bangkok: 92-93 [in Thai].

(7) Patrick David, 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)

(8) Indraneil Das, 2010. A Field Guide to the Reptiles of Thailand and South-East Asia. Asia Books, Bangkok: 300.

(9) Nikolai Orlov, Sergei Ryabov and Klaus-Dieter Schulz, 1999. Eine seltene Natter aus Nordvietnam, Rhynchophis boulengeri Mocquard, 1897 (Squamata: Serpentes: Colubridae). Sauria, Berlin, 21 (1): 3-8.

(10) In a report in 2004/5 following a find in Tak province, this province was considered as the second locality in Thailand where the species was known to occur. Vogel, G. and O. S. G. Pauwels (2004/5): Geographical distribution: Elaphe prasina. Herpetological Review, New York, 35(4): 410.