Daboia siamensis, the deadly Eastern Russell’s Viper
True vipers can be distinguished from pitvipers by the absence of a heat-sensing pit-organ and some other features. Like the pitvipers, they have long tubular fangs, but no other teeth on the short maxillary bone.
During a strike, the latter is rotated through an angle of about 90 degrees, swinging the fangs from a horizontal to a vertical position.
In Thailand, only one species of true vipers occurs, the Western Russell’s Viper.
The genus Daboia long been represented by a single species, Daboia russelii, the Russell’s viper, formerly known as Vipera russelii. Recently the species was split up in two distinct species, Daboia russelii from India (the Western Russell’s Viper) and Daboia siamensis from Southeast Asia (the Eastern Russell’s Viper).
Using albumin immunology and blood serum electrophoresis to examine the phylogeny of Eurasian viperines, the Russell’s viper was shown to occupy an isolated position and to be only distantly related to other Eurasian viperines, and subsequently the revalidation of the monotypic genus Daboia was proposed in 1992. (1)
Eastern Russell’s viper (Daboia siamensis)
Thai name: ngu maeo sao – งูแมวเซา
‘During the drag-hunt my attention, for some reason, is attracted by a strangely-formed, thick cudgel lying in front of my feet on the sandy ground, sparsely covered with grass. Watching it more attentively, I realize that it is a truly handsome specimen of the Russell’s viper, one of the most dangerous poisonous snakes of Burma. Should I release the load of pellets in the barrel of my gun onto the beautiful animal, only two meters before of me, I would have shattered it completely. So I hastily reload with a small cartridge. In the mean time the viper makes a rapid, gliding movement and has disappeared into a nearby hole before I am ready to shoot.’ (2)
Thus was German naturalist Gerd Heinrich’s encounter with a deadly Russell’s viper, a true viper of deadly repute, in the 1930s. Since this snake will often not attempt to flee when approached by humans — instead, it may hiss loudly and be ready to strike — Heinrich lacked the good luck for obtaining its beautiful skin.
True vipers such as the Russell’s viper lack the heat-sensing pit-organ of the pit vipers (Crotalidae). Until recently it was known as Vipera russelii, a name indicating a close relationship with such species as the common European viper (Vipera bera). Its seclusion into a separate genus, however, seems to be justified.
Its ‘new’ name ‘Daboia’ is the Hindi name for the snake, which means ‘the lurker’. In its range — from Pakistan to Taiwan and eastern Indonesia — five subspecies have been distinguished, but this has been reduced to two subspecies by Wüster, only acknowledging the western subspecies Daboia russelii russelii from India, Pakistan and Sri Lanka, and the eastern subspecies Daboia russelii siamensis from Myanmar, Thailand, Cambodia, Taiwan, southern China, Java and some other Indonesian islands. The latter is recently considered as a separate species on its own, Daboia siamensis Smith, 1917 (the ‘Eastern Russell’s Viper’). (3)
‘Russell’s’ and ‘russelii’ refer to dr Patrick Russell (1727-1805), the ‘Father of Indian Ophiology’ who at the end of the eightteenth century studied the dentition of harmless and poisonous snakes and conducted experiments on the toxicity of venoms. In 1796, Russell was the first who focused attention on this dangerous viper. The correct spelling of the name is still a matter of debate. Shaw and Nodder (1797), in their account of the species Coluber russelii, apparently misspelled his name, using only one “l”. Some authors favor the original, wrong spelling (4), others favor russellii. At present, this transgression on spelling only concerns the Western Russell’s Viper which occurs in India and Pakistan.
Identification, scalation and color of Daboia siamensis
The Thai subspecies of the Russell’s viper is a rather stout, round-bodied snake which may reach a length of 160 cm, making it the largest of all Viperidae (vipers and pitvipers) in Thailand. The dorsal scales are heavily keeled. The upper side is light brown to buff with three longitudinal rows of oval, dark brown spots. The larger spots have black borders edged with white, whereas the smaller ones may be completely black. There are further rows of smaller and narrow, well-defined spots between the three main rows, which are absent in Daboia russelii (the Indian species), a difference that appears to be absolutely diagnostic. (5)
Some of the large spots may be fused into a figure resembling an ‘8’. In Pakistan this viper is called ‘chain viper’, as many such fusions often result into a chain-like pattern. In Myanmar it is locally believed that such patterned serpents are so deadly that once bitten no treatment will avail. (6)
The head is covered with many tiny scales and camouflaged well with long, oval, brown spots, the dark eye being hidden in one of them.
The white underside is peppered with evenly spaced dark, half moon-shaped spots on the posterior edges of the ventral scales.
The coloration resembles that of the many-spotted cat snake (Boiga multomaculata), however, this rather mild-mannered snake has a very slender body which is covered with smooth scales. As its venom is weak, the marble cat snake is considered harmless.
Habitat and habits
This viper is not restricted to any particular habitat, but appears to prefer rather open country, such as secondary growth and shrub jungles, eucalyptus plantations, cultivated fields, bushes near marshy areas, grasslands bordering plantations, sandy grounds and rocky hills. It tends to avoid dense forests and humid environments, such as marches and swamps. During the hot season it may hide in termite moulds or rodent holes, or lie coiled between rocks. (7)
At night this terrestrial snake wanders about in slow, crawling motion, hunting for prey, such as rodents, lizards, and frogs. It is most active in the early evening, but during cool days it may be crepiscular. At daytime, one may come across specimens coiled up in open shelters. The light brown or buff skin with a pattern of dark brown, oval blotches harmonizes well with dried vegetation, and makes it difficult to see it on the ground. It sometimes climbs low trees.
When cornered it assumes a defensive posture by swelling its body and hissing forcefully, a ‘hiss once heard that is not easily forgotten,’ herpetologist Frank Wall once noted. Bunyuan and Wirot compare it with the sound of the air released from a punctured tire. (8) The hiss produced has a mean amplitude of over 82 dB, well above the intensity of most other snake sounds. The large external naris of this species probably increase the intensity of the hiss, functioning like the flare of a trumpet. (9)
Once irritated and striking from this position, it hurls itself with speed and bites with determination. It can exert so much force that even a large individual can lift most of its body off the ground in the process. Some specimens thrash around wildly, striking in all directions and moving surprisingly fast. (10) During a strike, it may spray venom before biting. Because of its nervous disposition and its unpredictable, lightning-like strike, you will see professionals — such as the men milking the venom in Bangkok’s snake farm at the Queen Saovabha Memorial Institute — handling Russell’s vipers with more care than any other venomous snake.
‘The bite is tenacious, powerful and certain to inflict damage by injecting a large amount of venom deep into the tissues of the victim,’ an expert from Burma put it. (11) It usually causes very serious envenomation, and it should be considered as the most dangerous viper of Southeast Asia and one of the most deadly snakes in the whole world. (12) In Burma, where it is more abundant than in Thailand, this snake is responsible for by far the largest number of fatalities (about 90 percent) among snake bite victims, making Burma the country with the highest death rate due to snake bite in the world and a ‘severe health problem’. (13)
The bite is extremely painful. The haemotoxic venom causes intense swelling and discoloration, and extensive bleeding of the gums and urogenital tracts, as the venom is a strong blood coagulant. Bleeding in the kidneys and pituitary often result to fatal organ failures. Reduced blood coagulability and renal failure are widespread, but a number of other phenomena show strong geographic variation. Bites in Sri Lanka and southern India also result in neurotoxicity, whereas bites in Thailand result mostly in intravascular haemolysis and reduced blood coagulability. These differences are related to profound differences in venom composition and enzymatic activity, which in turn may affect antivenom efficacy if an antivenom is used against the venom of populations other than those used for its preparation. (14)
In Thailand this snake is called ngu maeo sao which means ‘sleepy cat snake’, as it is locally believed that its venom causes some kind of motionless sleep. (15) In a study on Thailand’s traditional monks, it is recounted that a villager from Sangkhlaburi (in the upper part of Kanchanaburi, near the Burmese border) was bitten by a Russell’s viper and ‘felt sleepy all the time’. A monk specialized in herbal medicine kept him awake and administered a mixture of medicinal powder, lime juice and bile from a snake’s gall bladder to the wound. Within a day the patient recovered. (16)
This species is ovoviviparous and prolific and may give birth to over fifty babies, being 20 cm long replicas of the adults. The hemipenes are short and sturdy with a claw-like, protruding spine at the top, and many small spines pointing downwards along the basis.
In the North its distribution seems to be restricted to Uthai Thani and Nakhon Sawan provinces, where I recorded road-killed specimens in Mueang and Sawang Arom districts (Thai Thani) and Lat Yao district (Nakhon Sawan). It is more common in parts of Central-Thailand, in the area stretching from Chainat to the eastern province of Sa Kaeo at the Cambodian border, where I found road kills in Lopburi (Sa Bot district), Prachinburi (Kabinburi and Si Mahasot districts), Chachoengsao (Phanom Sarakham and Sanam Chai Khet districts), and Sa Kaeo (Muang, Khao Chakan and Watthana Nakhon districts). On the peninsula, its distribution seems to be as far to the south as Chumphon province (17), whereas ‘unambiguous’ descriptions were recorded from native people in Phang Nga province. (18) On the island Ko Chang, in Trat province in the eastern region, its presence has been confirmed by the Ko Chang Ecocentre. (19)
Within this range, there are areas where it is (or has been) extremely abundant (e.g. in some parts of Sa Kaeo province), whereas it appears to be virtually absent in others. An uneven, often scattered distribution has also been reported in other countries, such as on Java in Indonesia. According to Leviton and others, this erratic distribution suggests that it has been transported in the course of commercial exchanges, likely during the 18th and 19th centuries, as it is a prolific breeder — the young could easily have been transported among plants and other products that were frequently carried about during the early days of colonial expansion. (20)
©Sjon Hauser: text, pictures and map.
(1) In: Wüster, Wolfgang, 1998. The genus Daboia (Serpentes: Viperidae): Russell’s viper. Hamadryad, 23 (1): 33-40 (p. 33).
(2) Heinrich, Gerd, 1942. In Burmas Bergwäldern. Forschungsreise in Britisch-Hinterindien. Verlag von Dietrich Reimer, Andrews & Steiner, Berlin: 84-85.
(3) E.g. Cox et al., 2012. The snakes of Thailand. Chulalongkorn Museum of Natural History, Bangkok (p. 726-729); and Das, Indraneil, 2012. A naturalist’s guide to the snakes of Thailand and Southeast Asia. Asia Books, Bangkok (p. 74).
(4) Citing Article 32c (ii) of the International Code of Zoological Nomenclature.
(5) Wüster, 1998, ibid.: 34.
(6) Maung Maung Aye, 1990: 219.
(7) Cox, 1991: 407.
(8) Thumwiphat and Nutphan, 1982: 80.
(9) Young, 1998.
(10) Wüster, 1998: 37.
(11) Maung Maung Aye, 1990: 211-241.
(12) Parker and Grandison, 1977: 91.
(13) Maung Maung Aye, 1990.
(14) In: Wüster, 1998: 37-38.
(15) Cox, 1991: 499.
(16) Tiyavanich, 2003: 182-183.
(17) Cox, 1991; 408.
(18) Pauwels et al., 2000: 149.
(19) Stan Klaassens, personal communication.
(20) Leviton et al., 2003: 440.