Bungarus

Bungarus

Bungarus is a genus of venomous elapid snakes found in India and South-East Asia. Commonly referred to as kraits, there are 12 species and 5 subspecies.

Distribution

Kraits are found in the Indian subcontinent (including Sri Lanka and eastern Pakistan) and southeast Asia (including Indonesia and Borneo).

Description

Kraits usually range between 1 to 1.5 m in length, although specimens as large as 2 m have been observed. The Banded Krait (B. fasciatus) may grow as large as 2.5 m. Most species of krait are covered in smooth glossy scales that are arranged in bold striped patterns of alternating black and light-colored areas. This gives the snake camouflage in its habitat of grassland and scrub jungle. The scales along the dorsal ridge of the back are hexagonal. The head is slender and the eyes have round pupils. Kraits have a pronounced dorso-lateral flattening, and are triangular in cross-section. The tail tapers to a thin point.

Reproduction

Kraits are oviparous and the female will lay a clutch of 6 to 12 eggs in piles of leaf litter and stay with them until they hatch.

Diet & Behavior

Kraits are ophiophagous, preying primarily upon other snakes (including venomous varieties) and are cannibalistic, feeding on other kraits. They will also eat small lizards.

All kraits are nocturnal. The snake is more docile during the daylight hours, becoming more aggressive during the night. However, they are rather timid and will often hide their heads within their coiled bodies for protection. When in this posture, they will sometimes whip their tail around as a type of distraction.

Venom

Bungarus species contain neurotoxic venom that is 16 times more potent than cobra venom. Krait venom is extremely powerful and quickly induces muscle paralysis. Clinically, their venom contains mostly pre-synaptic neurotoxins. These affect the ability of nerve endings to properly release the chemical that sends the message to the next nerve. Following envenomation with bungarotoxins, transmitter release is initially blocked (leading to a brief paralysis), followed by a period of massive overexcitation (cramps, tremors, spasms), which finally tails off to paralysis. Not all these phases may be seen in all parts of the body at the same time..

Fortunately, since kraits are nocturnal they seldom encounter humans during daylight hours so bites are rare. Nonetheless, any bite from a krait is potentially life-threatening and must therefore be regarded as a medical emergency. Note that there is frequently little or no pain at the site of a krait bite and this can provide false reassurance to the victim. Typically, victims start to complain later of severe abdominal cramps accompanied by progressive muscular paralysis, frequently starting with ptosis. As there are no local symptoms, a patient should be carefully observed for tell-tale signs of paralysis (e.g. the onset of ptosis, diplopia and dysphagia) and treated urgently with antivenom. Before antivenom was developed, there was an 85% mortality rate among bite victims.

Krait antivenom is often ineffective for species in the genus other than the snake originally included in the antivenom preparation. Often noted on lay websites is the statement that there is a mortality rate of 50% even with treatment , but there is no original source in the medical literature for this statement. Mortality remains high given that many patients envenomated never make it to healthcare facilities due to the distance from their rural homes and the often profound lack of medical resources, especially intubation supplies and mechanical ventilators in rural hospitals. Definitive care may also be delayed as patients may first visit the local mantrik or tantrik, a holy person and traditional healer who may attempt to rid the body of the venom with spells or herbal remedies, which are ineffective interventions.

Once at a healthcare facility such support should be provided until the venom is metabolised and the victim can breathe unaided especially if there is no species-specific antivenom available. Given that the toxins alter acetylcholine transmission which causes the paralysis, some patients have been successfully treated with cholinesterase inhibitors such as physostigmine or neostigmine, but success is variable and may be species dependent as well. If death occurs it typically takes place approximately 6 to 12 hours after the krait bite, but can be significantly delayed. Cause of death is often respiratory failure ie suffocation via complete paralysis of the diaphragm. Even if patients make it to a hospital subsequent permanent coma and even brain death from hypoxia may occur given potentially long transport times to get medical care.

In 2001, herpetologist Dr. Joe Slowinski was bitten by a juvenile krait (B. multicinctus) while doing field research in Myanmar. He was unable to reach medical assistance and subsequently died from the effects of the bite.

Species

Species Authority Subsp.* Common name Geographic range
B. andamanensis Biswas & Sanyal, 1978 0 South Andaman krait India (Andaman Island)
B. bungaroides Cantor, 1839 0 Northeastern hill krait Myanmar, India (Assam, Cachar, Sikkim), Nepal, Vietnam
B. caeruleus Schneider, 1801 0 Indian krait Afghanistan, Pakistan, India (Maharashtra, Karnataka, Sri Lanka, Bangladesh, Nepal
B. candidus Linnaeus, 1758 0 Malayan krait, Blue krait Cambodia, Indonesia (Java, Sumatra, Bali, Sulawesi), Malaysia (Malaya), Singapore, Thailand, Vietnam
B. ceylonicus Günther, 1864 1 Ceylon krait Sri Lanka
B. fasciatus Schneider, 1801 0 Banded krait Bangladesh, Brunei, Myanmar, Cambodia, south China (incl. Hong Kong, Hainan), north-east India, Bhutan, Nepal, Indonesia (Sumatra, Java, Borneo), Laos, Macau; Malaysia (Malaya and East Malaysia), Singapore, Thailand, Vietnam
B. flaviceps Reinhardt, 1843 1 Red-headed krait South Thailand, South Myanmar, Cambodia, Vietnam, Malaysian Peninsula, Pulau Tioman, Indonesia (Bangka, Sumatra, Java, Billiton, Borneo)
B. lividus Cantor, 1839 0 Lesser black krait India, Bangladesh, Nepal
B. magnimaculatus Wall and Evans, 1901 0 Burmese krait Myanmar
B. multicinctus Blyth, 1861 1 Many-banded Krait Taiwan, south China (incl. Hong Kong, Hainan), Myanmar, Laos, north Vietnam, Thailand
B. niger Wall, 1908 0 Black krait India (Assam, Sikkim), Nepal, Bangladesh, Bhutan
B. sindanus Boulenger, 1897 2 Sind krait South-east Pakistan, India
*) Not including the nominate subspecies (typical form).

Kraits in fiction

Kraits have reputations as deadly snakes and have figured in fiction as such. Rudyard Kipling used a small, sand colored krait as one of the three main villains in his short story Rikki-Tiki-Tai. (The other two villains being a couple of Black Cobras)

Roald Dahl uses the krait as a device in his short story "Poison." The krait also appears in Frederick Forsyth's short story "There Are No Snakes in Ireland" (referencing Kipling's Rikki-Tiki-Tavi, with the assumption that Kipling may actually have meant the Saw-scaled viper; included in his collection No Comebacks).

It has also been argued that the deadly snake in the Sherlock Holmes story The Adventure of the Speckled Band may have been a krait, although it is described in that work as an "Indian swamp adder." (The Russell's Viper has also been considered as a possible culprit.)

In a slightly more oblique reference, the motion picture Snakes on a Plane features a villainous snake smuggler named "Kraitler."

In Dean Koontz's "The Good Guy", the hitman assigned to murder one of the protagonists calls himself Krait.

In Guild Wars Eye Of the North there is a race of snake-like creatures called Krait.

In Mercedes Lackey's "The Serpent's Shadow", Maya's father was killed by a krait while living in India.

In the Star Wars: Legacy comic book series, the leader of the New Sith Order is known as Darth Krayt. Though named after the fictional Krayt Dragon, it is possible that the venomous dragon was named after the krait.

References

External links

[[zh:環蛇屬]

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