The common krait's bite can be so painless that sleepers never wake
Most dangerous snakes announce a bite with pain and swelling. South Asia's common krait often does not. Its fangs are small and its venom causes almost no damage at the site, so a person asleep on the floor at night may not notice being bitten until paralysis begins hours later.
Bungarus caeruleus is a glossy black or blue-black snake crossed by around 40 thin white bands, usually about 0.9 metres long but occasionally reaching 1.75. It lives across India, Pakistan, Bangladesh, Sri Lanka and Nepal, in scrub, farmland, semi-desert and suburban gardens, often near water and wherever rats are plentiful. By day it hides in rodent burrows, termite mounds or rubbish, and in the monsoon it frequently slips into houses. It is one of India's big four snakes blamed for most bites, and it causes the majority of the serious ones on the subcontinent.
Temperament is not the problem. The krait is shy and rarely bites unless provoked, and when threatened it typically coils tightly and hides its head beneath its body. It hunts at night, mainly eating other snakes, including vipers and fellow kraits, along with rodents, lizards and frogs. Females lay 5 to 15 eggs and, unusually for snakes, guard them for about 60 days until they hatch; the young emerge already venomous.
The venom is almost purely a nerve poison. About 64.5 percent of it consists of enzymes called phospholipases, led by beta-bungarotoxins that wreck the nerve endings which release the chemical signal telling muscles to contract. A further 15 to 19 percent blocks the receiving side of that signal. Because the damage is presynaptic, a drug that helps against cobra venom does little here. There are no tissue-destroying components, which is why bites look so innocent. An average bite delivers about 10 milligrams, while an estimated 2 to 3 milligrams can kill a person.
Untreated, the paralysis spreads until breathing fails, and one clinical study put untreated mortality at 70 to 80 percent. Many bites are dry, carrying no venom at all. Current antivenoms save lives, but researchers want versions better matched to regional differences in the venom.
Source: Common krait
