Reptiles and Amphibians of Thailand

Thailand's Snakes, Lizards, Turtles, and Frogs

Triangled Black-headed Snake

Sibynophis triangularis

This species is found in Thailand, but not within Bangkok itself
Triangled Black-headed Snake Triangle Many-toothed Collared Sibynophis triangularis งูคอขวั้นหัวลายสามเหลี่ยม thailand
potential Triangled Black-headed Snake in Khao Yai National Park (© Guy Haimovitch)

The following photos all represent potential Triangled Black-headed Snakes (Sibynophis cf. triangularis) due to their somewhat triangle-shaped black nuchal mark and broad cream band continuing from the lip stripe. It is difficult to confirm their identity due to uncertainties in the key for Sibynophis, explained below.

English name: Triangled Black-headed Snake (aka: “Triangle Many-toothed Snake”, “Triangle Collared Snake”)
Scientific name: Sibynophis triangularis
Thai name: งูคอขวั้นหัวลายสามเหลี่ยม (Ngu Ko-kwan Hua Lai Sam Leeam)

Description: To 70cm. Slender body is grayish-brown at front and darker gray towards back, sometimes with black dots on top of the body and two rows of pale dots forming dorsolateral stripes. Head is grayish with two black crossbars on top. Black triangle on back of neck is bordered by broad cream lines continuous with cream lines on lips. Belly is white with black dots on the edge.

Relevant scale counts: 17 midbody scale rows with smooth dorsal scales. 10 supralabials of which the 10th is largest. Parietal scale touches only the upper postocular. 113-124 subcaudals.

Similar Species: Collared Black-headed Snake has a less triangle-shaped mark on back of neck, bordered more thinly with a light line that may not proceed from the lip, and the 8th supralabial is the largest.
White-lipped Black-headed Snake has black bars on the light ventrolateral line, white lip lines that stop before forming a chevron on the neck, 9 supralabials and 132-136 subcaudals.

Range: Thailand and Cambodia.

Habitat: Hilly lowland forest up to 1000m elevation.

Place in the ecosystem: Likely feeds on skinks, small snakes, frogs and insects. Would be eaten by larger snakes, monitors, civets, and birds of prey.

Danger to humans: Is not dangerous to humans.

Conservation status and threats: It is known from relatively few locations and may be threatened by deforestation.

Interesting facts: The Triangled Black-headed Snake was originally described as a new subspecies by Edward Taylor and Robert Elbel in 1958 and then elevated to species status by Taylor in 1965. In his key to the genus, which was based on limited specimens, the Triangled Black-headed Snake was distinguished from the Collared Black-headed Snake by its triangle-shaped nuchal mark, the cream lines bordering the mark being broad and continuous with the lips, and the 10th supralabial being largest rather than the 8th. However, actual black-headed snakes in the field show a large range of nuchal mark shapes, some more triangular than others, and it is difficult to pin down exactly how triangular the mark should be to distinguish the species. Similarly, the cream line is sometimes continuous with the lips even in snakes without a triangular mark, may or may not broaden, and the 8th supralabial and 10th supralabial appear similar in size in some specimens. Since Taylor’s 1965 paper, no one has done a systematic study of the genus, and it will take significantly more examination of specimens across Thailand and their broader range, possibly along with genetic studies, to conclusively determine whether the Triangled Black-headed Snake is a valid species and how it should definitively key out.

References:
IUCN Red List: Triangled Black-headed Snake
Thai National Parks: Triangle Collared Snake
Contributions to the Herpetology of Thailand
Serpents of Thailand and its Waters
A collection of amphibians and reptiles from hilly Eastern Cambodia
Gernot Vogel pers. comm.
Bryan Stuart pers. comm.
Reptiles of South-east Asia

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