Thai National Parks

Species of Thailand

Malayan pit viper

Calloselasma rhodostoma

(Heinrich Kuhl, 1824)

In Thai: งูกะปะ, ngu ga pha

Calloselasma is a monotypic genus created for a venomous pit viper species, Calloselasma rhodostoma, which is endemic to Southeast Asia from Thailand to northern Malaysia and on the island of Java. No subspecies are currently recognized.


Attains an average total length of 76 cm, with females being slightly longer than males. Occasionally, they may grow as long as 91 cm.

A specimen with a total length of 81 cm has a tail 9 cm long.

Dorsally it is reddish, grayish, or pale brown, with two series of large, dark brown, black-edged triangular blotches, which are alternating or opposite. There is also a thin dark brown vertebral stripe, which may be interrupted or indistinct in some specimens. The upper labials are pink or yellowish, and powdered with brown. There is a broad, dark brown, black-edged diagonal stripe from the eye to the corner of the mouth, with a narrower light-colored stripe above it. Ventrally it is yellowish, uniform or powdered or spotted with grayish brown.

The smooth dorsal scales are arranged in 21 rows at midbody. Ventrals 138-157; anal plate entire; subcaudals 34-54 pairs.

Snout pointed and upturned. Rostral as deep as broad. Two internasals and two prefrontals. Frontal as long as or slightly longer than its distance from tip of snout, as long as or slightly shorter than the parietals. 7-9 upper labials. Loreal pit not in contact with the upper labials.

This is the only Asian pit viper with large crown scales and smooth dorsal scales.

Geographic range

Found in Nepal, Thailand, Cambodia, Laos, Vietnam, northern West Malaysia and on the Indonesian island of Java. The type locality is listed as "Java". There are unconfirmed, but credible reports from southern Myanmar (Burma), northern Sumatra and northern Borneo.

Habitat and diet

Prefers coastal forests, bamboo thickets, unused and overgrown farmland, orchards, plantations as well as forests around plantations, where it searches for rats and mice.


This species is oviparous and the eggs are guarded by the female after deposition.


This species has a reputation for being bad-tempered and quick to strike. In northern Malaysia it is responsible for some 700 incidents of snakebite annually with a mortality rate of about 2 percent. Remarkably sedentary, it has often been found in the same spot several hours after an incident involving humans. Its venom causes severe pain and local swelling and sometimes tissue necrosis, but deaths are not common. Many victims are left with dysfunctional or amputated limbs due to the lack of antivenom and early treatment. In a 2005 study of 225 Malayan pit viper (Calloselasma rhodostoma) bites in Thailand, most victims had mild to moderate symptoms, but 27 of 145 patients (18.6%) developed permanently swollen limbs. There were only two deaths (related to intracerebral hemorrhage) and no amputations. The antivenin manufactured in Thailand seemed effective in reversing the blood clotting caused by the venom. Most patients remained stable and did not require antivenin. The authors suggested that victims not use traditional healers and avoid overuse of tourniquets. In a prospective phase of the study, bites occurred throughout the year but mostly early in the monsoon season (May and June).

Venom and thrombosis treatment

The venom of this species is used to isolate a thrombin-like enzyme called ancrod. This enzyme is used clinically to break down and dissolve thrombi (blood clots) in patients and lower blood viscosity to help prevent heart attack and stroke.

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Scientific classification

Calloselasma rhodostoma

Common names

  • German: Malaiische Mokassin-Grubenotter
  • English:
    • Malayan pit viper
    • Malayan ground pit viper
    • Malayan ground snake
    • Malayan moccasin
  • Thai: งูกะปะ, ngu ga pha


  • Calloselasma rhodostoma annamensis, Fernand Angel, 1933

    Range: Southeast Cambodia and Vietnam

  • Calloselasma rhodostoma rhodostoma, Friedrich Boie, 1827

    Range: South Vietnam (Binh Thuan etc.), Cambodia, Thailand, Laos, West Malaysia and Indonesia (Java).


  • Calloselasma rhodostoma, Van Stanley Bartholomew Wallach et al. (2014)
  • Calloselasma rhodostoma, Nguyen Van Sang et al. (2009)
  • Calloselasma rhodostoma, Roy W. McDiarmid, Jonathan A. Campbell & T'Shaka A. Touré (1999)
  • Calloselasma rhodostoma, Merel J. Cox et al. (1998)
  • Calloselasma rhodostoma, Ulrich Manthey & Wolfgang Grossmann (1997)
  • Calloselasma rhodostoma, Kenneth Welsh (1994)
  • Calloselasma rhodostoma, Simon M Campden-Main (1970)
  • Ancistrodon rhodostoma, Malcolm Arthur Smith (1943)
  • Agkistrodon annamensis, René Léon Bourret (1936)
  • [Agkistrodon] annamensis, Clifford H. Pope (1935)

Conservation status

Least Concern (IUCN3.1)

Least Concern (IUCN3.1)


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Calloselasma rhodostoma - Tha Chana District, Surat Thani
Calloselasma rhodostoma
Calloselasma rhodostoma
Calloselasma rhodostoma
Calloselasma rhodostoma - Hua Hin District
Calloselasma rhodostoma
Calloselasma rhodostoma
Calloselasma rhodostoma
Calloselasma rhodostoma

Range Map

Distribution map of Malayan pit viper, Calloselasma rhodostoma in Thailand
  • Ao Luek District, Krabi
  • Ban Chang District, Rayong
  • Ban Laem District, Phetchaburi
  • Ban Lat District, Phetchaburi
  • Bang Lamung District, Chonburi
  • Bang Saphan District, Prachuap Khiri Khan
  • Bannang Sata District, Yala
  • Bo Thong District, Chonburi
  • Cha-Am District, Phetchaburi
  • Chaloem Phra Kiat District, Nan
  • Chiang Khan District, Loei
  • Chulabhorn District, Nakhon Si Thammarat
  • Doi Suthep - Pui National Park
  • Don Sak District, Surat Thani
  • Hat Yai District, Songkhla
  • Hua Hin District, Prachuap Khiri Khan
  • Huai Kha Khaeng Wildlife Sanctuary
  • Huai Yot District, Trang
  • Kabang District, Yala
  • Kabin Buri District, Prachinburi
  • Kaeng Hang Maeo District, Chanthaburi
  • Kaeng Khoi District, Saraburi
  • Kaeng Krachan District, Phetchaburi
  • Kaeng Tana National Park
  • Kanchanadit District, Surat Thani
  • Kantang District, Trang
  • Kap Choeng District, Surin
  • Khanom District, Nakhon Si Thammarat
  • Khao Chamao - Khao Wong National Park
  • Khao Nam Khang National Park
  • Khao Nan National Park
  • Khao Phra - Bang Khram Wildlife Sanctuary
  • Khao Soi Dao Wildlife Sanctuary
  • Khao Sok National Park
  • Khao Yoi District, Phetchaburi
  • Khemarat District, Ubon Ratchathani
  • Khiri Mat District, Sukhothai
  • Khlong Hoi Khong District, Songkhla
  • Khlung District, Chanthaburi
  • Khun Nan National Park
  • Klaeng District, Rayong
  • Ko Lanta District, Krabi
  • Kumphawapi District, Udon Thani
  • Laem Sing District, Chanthaburi
  • Lan Sak District, Uthai Thani
  • Lom Sak District, Phetchabun
  • Mae Chaem District, Chiang Mai
  • Mae Suai District, Chiang Rai
  • Mae Taeng District, Chiang Mai
  • Makham District, Chanthaburi
  • Mueang Chiang Mai District, Chiang Mai
  • Mueang Krabi District, Krabi
  • Mueang Loei District, Loei
  • Mueang Lopburi District, Lopburi
  • Mueang Nakhon Phanom District, Nakhon Phanom
  • Mueang Nakhon Si Thammarat District, Nakhon Si Thammarat
  • Mueang Nongbua Lamphu District, Nong Bua Lamphu
  • Mueang Pan District, Lampang
  • Mueang Prachuap Khiri Khan District, Prachuap Khiri Khan
  • Mueang Surat Thani District, Surat Thani
  • Mueang Trang District, Trang
  • Na Di District, Prachinburi
  • Na Mom District, Songkhla
  • Nam Nao National Park
  • Nikhom Phatthana District, Rayong
  • Nong Han District, Udon Thani
  • Nong Khae District, Saraburi
  • Nong Phok District, Roi Et
  • Nong Wua So District, Udon Thani
  • Nopphitam District, Nakhon Si Thammarat
  • Pak Phli District, Nakhon Nayok
  • Pang Sida National Park
  • Pathio District, Chumphon
  • Pha Taem National Park
  • Phrom Khiri District, Nakhon Si Thammarat
  • Phu Khiao Wildlife Sanctuary
  • Phu Phan National Park
  • Phu Si Than Wildlife Sanctuary
  • Phu Wua Wildlife Sanctuary
  • Phunphin District, Surat Thani
  • Plai Phraya District, Krabi
  • Pran Buri District, Prachuap Khiri Khan
  • Pua District, Nan
  • Rattaphum District, Songkhla
  • Ron Phibun District, Nakhon Si Thammarat
  • Royal Chumphon Forest Park
  • Sadao District, Songkhla
  • Sai Buri District, Pattani
  • Sai Yok National Park
  • Sakaerat Environmental Research Station
  • Sam Roi Yot District, Prachuap Khiri Khan
  • Sangkhom District, Nong Khai
  • Sathing Phra District, Songkhla
  • Sattahip District, Chonburi
  • Sawi District, Chumphon
  • Si Racha District, Chonburi
  • Si Songkhram District, Nakhon Phanom
  • Sikao District, Trang
  • Soem Ngam District, Lampang
  • Sri Nakarin Dam National Park
  • Sukhirin District, Narathiwat
  • Ta Phraya National Park
  • Tamot District, Phatthalung
  • Tha Chana District, Surat Thani
  • Tha Li District, Loei
  • Tha Mai District, Chanthaburi
  • Tha Pla District, Uttaradit
  • Tha Sae District, Chumphon
  • Tha Takiap District, Chachoengsao
  • Tha Yang District, Phetchaburi
  • Thale Ban National Park
  • Thong Pha Phum District, Kanchanaburi
  • Thung Chang District, Nan
  • Thung Song District, Nakhon Si Thammarat
  • Thung Tako District, Chumphon
  • Ton Nga-Chang Wildlife Sanctuary
  • Wang Thong District, Phitsanulok
  • Wang Wiset District, Trang
  • Yan Ta Khao District, Trang
  • Yod Dom Wildlife Sanctuary
Range map of Calloselasma rhodostoma in Thailand