The Dark Knight: Enigma of the Common Krait

“Dangerous” is the most frequent label used to describe the common krait. This snake has the reputation of being the deadliest snake within its geographical distribution, and all snakes that look remotely like it also suffer because of this. However, the common krait (Bungarus caeruleus) has done little to earn this reputation.

The word “krait” is derived from the Hindi word for the species, karait. This is the name common kraits are known by in Madhya Pradesh and some parts of Uttar Pradesh, though the origins of the word are unknown.

Snake eat snake
From personal experience, I do know that the common krait is a mild tempered snake, fleeing from disturbance as fast as it can. It only comes out in the dead of night, keeping away from light and activity, hunting for prey in the shadows. Unlike some of its cousins, such as the banded krait (Bungarus fasciatus) that feeds almost exclusively on snakes, the common krait seems to have a wider prey base. Common kraits feed largely on other snakes and reptiles like lizards, but will also capture and consume small rodents, especially field mice of the Mus genus. It also eats frogs and insects.

Potent toxin
This species has also been credited with having the most potent venom of any snake in India. However, recent research shows that at least one species, the Sind krait (Bungarus sindanus), has venom that is five times more potent. Still, the common krait’s venom is not to be taken lightly. It largely consists of an extremely potent, presynaptic neurotoxin that blocks signals from the nerve endings from being transmitted to the receptors on the muscles. Although the venom has a few other neurotoxic elements to it, it possesses no cytotoxic (affecting cells/tissue), haematotoxic (affecting blood), or other components. This is the good news. The venom affects the nervous system and does something of a “system shutdown” on the victim. Fortunately, the heart isn’t controlled by the central nervous system and as long as the patient can be given oxygen, the heart will keep beating. Many patients have recovered completely though they may have needed to be put on a ventilator. The bad news is that this kind of venom generally works faster than others. Even so, tales of a bite from this snake killing people in a matter of minutes are nonsense. Many people actually end up in hospital only several hours after they have been bitten.

The nature of its venom is another reason why the common krait has received its deadly reputation. In some parts of India, people believe that the krait doesn’t bite, but coils itself around the chest of its sleeping victims and sucks the breath out of them. Now the common krait’s venom causes, among other neurotoxic symptoms, difficulty in breathing and eventually, asphyxia, because the diaphragm stops moving. The fact that the species has tiny fangs and the bite causes little to no pain bolsters these superstitions.

Night crawler
Interestingly, there has been much debate about kraits biting people in their sleep. In rural India, many people sleep on the floor or out on the ground in front of their houses. Especially in Maharashtra, kraits have been known to occasionally bite people who sleep on the floor. Till recently, it was thought that this phenomenon happens because the person might roll over onto the snake, causing it to bite in self-defence. However, the numbers of bites from this scenario are too high for this to be the only reason rural Maharashtra receive dozens of krait bite victims like this a year. Another theory is that kraits are looking for feed and quite often, sheets, blankets, and even clothes might smell of mice because the rodents are so rampant in rural huts and houses. The snakes might simply be mistaking movement (in pitch darkness) for prey. Feeding responses like this are known from captive scenarios, where, snakes will strike out in a predatory way, rather than in defence because they have misidentified the handlers’ activity and are expecting food. This would also explain the intensity of the bites, as it would make sense that the snake would inject more venom as a feeding response than as a defensive one. Still, all this is speculation until someone can do a controlled study.

The common krait’s habits don’t do its reputation any favours. It is active in the dead of night, and often found close to human habitation. The species loves crevices and holes in walls — a feature that is all too common in rural houses. It is this reality that brings kraits and humans into the largest conflict.

The species moves more fluidly than many other snakes, its white pin-stripe bands making it hard to follow visually. The bands, interestingly, reflect UV light quite strongly unlike some other nocturnal striped snakes like wolf snakes. Nobody quite knows why this is. But, it certainly warrants some level of research.

Krait basics
What we do know about common kraits is the basics. It averages about 90 cm in length with males growing longer than females. However, 1.5 m specimens are not unheard of. We know that in South India, mating occurs in December and females lay between 5-15 eggs in February. Young appear in April. These tiny ballpoint pen refill thick hatchlings are brilliantly marked. They often have a collar around their necks that fades along with many of the anterior bands as they grow older. Not much is known about what they might eat at this size, but, the common belief is that they eat a large number of insects, worm snakes, and hatchling lizards.