Reptiles and Amphibians of Thailand

Thailand's Snakes, Lizards, Turtles, and Frogs

Assam Mountain Snake

Plagiopholis nuchalis

This species is found in Thailand, but not within Bangkok itself
Assam Mountain Snake Burmese Arrowhead Snake Plagiopholis nuchalis thailand งูหัวลายลูกศร
Assam Mountain Snake eating worm in Chiang Mai (© Sjon Hauser)

English name: Assam Mountain Snake (aka: “Assamese Mountain Snake”, “Burmese Mountain Snake”)
Scientific name: Plagiopholis nuchalis
Thai name: งูหัวลายลูกศร (Ngu Hua Lai Luk-son)

Description: To 50cm. A stout snake with a small head that flattens at the end. Body is dark brown, reddish-brown, or yellowish-brown, sometimes with indistinct black bands across the body. There are blackish (in some cases whitish or yellowish) edges on the scales. Neck has a distinct black “chevron” mark on the top, though in some individuals it is reduced to a narrow black streak. This species can rear up and spread its neck to a degree as a defensive display. Belly is cream with black or brown rectangular marks on the scales.

Relevant scale counts: 15 midbody scales. Has a loreal shield, 2 posterior temporals, and 6 supralabials of which the 3rd and 4th are in contact with the eye and the 5th is largest. Only the 3rd supralabial touches the eye and the 4th is largest.

Similar Species: Blakeway’s Mountain Snake rarely has a prominent black chevron and has no loreal shield, 0-1 posterior temporals, and 5 supralabials of which only the 3rd supralabial is in contact with the eye and the 4th supralabial is largest. 
Chinese False Cobra has a broader and often indistinct or faded neck blotch, a larger eye, blunted snout, longer tail, belly blotches which only appear on the front half of the body, and 17 rows of midbody scales.

Range: South China, Myanmar, Laos, and mountainous areas of western, northern, and central Thailand.

Habitat: Moist mountain forests at elevations from 600m to 1620m.

Place in the ecosystem: Feeds on earthworms. Would be eaten by larger snakes, civets, and birds of prey.

Danger to humans: Is a rear-fanged snake like other members of its family, but is not dangerous to humans. However, when threatened it will rear up in a display shockingly similar to that of a cobra.

Conservation status and threats: This species has a broad range, but deforestation due to agriculture, logging, and various development could be placing it at risk.

Interesting facts: Though the common name of this snake is most commonly “Assam Mountain Snake” or “Assamese Mountain Snake”, it appears that it may not live in Assam or anywhere in India at all! The traditional connection of the snake with Assam is likely based on a misidentification. Due to this error, some herpetologists are attempting to popularize “Burmese Mountain Snake” or “Arrowhead Snake” as a more appropriate common name.

References:
IUCN Red List: Plagiopholis nuchalis
Thai National Parks: Assam Mountain Snake
Snakes of Northern Thailand: Mock Cobras
Sjon Hauser, personal communication.
Valid or not? Yunnan mountain snake Plagiopholis unipostocularis
First record of Blakeway’s mountain snake from Thailand, Tillack et al.

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