The average length is, but they can grow to. Males are longer, with proportionately longer tails. The head is flat and the neck hardly evident. The body is cylindrical, tapering towards the tail. The tail is short and rounded. The eyes are rather small, with rounded pupils, indistinguishable in life. The head shields are normal, with no loreals; four shields occur along the margin of the lower lip; the third and fourth supraoculars touch the eye. The scales are highly polished, in 15-17 rows; the vertebral row is distinctly enlarged and hexagonal. Ventrals number 185-225 and caudals 37-50, entire. Colouration is generally black or bluish black, with about 40 thin, white crossbars which may be indistinct or absent anteriorly. The pattern, however, is complete and well defined in the young, which are marked with conspicuous crossbars even anteriorly; in old individuals, the narrow white lines may be found as a series of connected spots, with a prominent spot on the vertebral region. A white preocular spot may be present; the upper lips and the belly are white.
This species is found in main Peninsular India from Sindh, to the West Bengal plains and also in Dharmanagar, Tripura. It occurs throughout South India and Sri Lanka at elevations up to about 1600 m. It is also recorded from Afghanistan, Bangladesh, and Nepal. Its range comprises a wide variety of habitats. It is found in fields and low scrub jungle, as well as inhabited areas. It is known to take up residence in termite mounds, brick piles, rat holes, even inside houses. It is frequently found in water or in proximity to a water source.
Feeding
The common krait feeds primarily on other snakes, including: "blind worms" ; and cannibalizes on other kraits, including the young. It also feeds on small mammals, lizards and frogs. The young are known to eat arthropods.
Behaviour
Behavioral differences during day and night time have been reported in B. caeruleus. During the day, it is sluggish and generally docile. It often hides in rodent holes, loose soil, or beneath debris, so is rarely seen. It often rolls its body into a loose, coiled ball, keeping its head well concealed. When in this 'balled' condition, the snake allows considerable handling, but overhandling often instigates bites. However, at night, the snake is very active and escapes by hissing loudly, or keeping still, occasionally biting the source of the annoyance. When agitated, it will coil up with its head concealed and body flattened, and makes jerky movements. It may also lift its tail. It is reluctant to bite, but when it does, it typically holds on for a while, which enables it to inject considerable amounts of venom. It may become aggressive at night if threatened since this is its active time. Its responsible for 2nd most snake bites in India. In Bangladesh its responsible for 28% of total Krait bites.
Venom
The common krait's venom consists mostly of powerful neurotoxins, which induce muscle paralysis. Clinically, its venom contains presynaptic and postsynaptic neurotoxins, which generally affect the synaptic cleft. In mice, the values of its venom are 0.325 mg/kg SC, 0.169 mg/kg IV and 0.089 mg/kg IP. and the average venom yield is 10 mg. Kraits are nocturnal, so seldom encounter humans during daylight hours; incidents occur mainly at night. Frequently, little or no pain occurs from a krait bite, and this can provide false reassurance to the victim. Typically, victims complain of severe abdominal cramps, accompanied by progressive paralysis. If death occurs, it takes place about four to eight hours after the krait bite. Cause of death is general respiratory failure, i.e. suffocation. Often during the rainy season, the snakes come out of their hiding places and find refuge inside dry houses. If bitten by a krait while sleeping, a victim may not realize he has been bitten, as the bite feels like that of an ant or mosquito. The victim may die without waking up. Krait bites are significant for eliciting minimal amounts of local inflammation/swelling. This may help in species identification if the snake has not been seen. The few symptoms of the bite include: tightening of the facial muscles in one to two hours of the bite; inability of the bite victim to see or talk, and, if left untreated, the patient may die from respiratory paralysis within four to five hours. A clinical toxicology study gives an untreated mortality rate of 70-80%. In Bangladesh, more than 50% of total snake bite deaths are caused by the common krait.
