King cobra

Name and taxonomy

The Danish naturalist Theodore Cantor described the species in 1836 as Hamadryas hannah, from three snakes taken in the Sundarbans and one near Kolkata. He never explained the name hannah, and it may honour Hannah Sarah Wallich, the daughter of his uncle and host, the botanist Nathaniel Wallich. Albert Günther proposed the genus Ophiophagus in 1864, because Hamadryas was already the name of a butterfly. Charles Bogert confirmed Ophiophagus hannah as the valid name in 1945 after showing how much the snake differs from the Naja cobras. Older books call it the hamadryad.

The oldest name of all, Naja bungaroides, was given by Friedrich Boie in 1828 for a young snake from Java. By a mix-up in 1837 that name ended up on an Australian snake, and the error was found only in 2024. Taxonomists chose to keep the familiar names rather than upend two centuries of literature. A 2021 genetic study and a 2024 revision split the king cobra into four species. O. hannah, the northern king cobra, keeps the old name. The Sunda, Western Ghats and Luzon king cobras became O. bungarus, O. kaalinga and O. salvatana.

Evolution and relatives

The king cobra belongs to the family Elapidae, which also holds the true cobras, kraits, mambas, coral snakes and sea snakes. Genetic studies using cytochrome b and several other genes place it as an early branch of the line that led to the mambas. So its hood and its name are a case of resemblance, not close kinship, with the Naja cobras. Cantor noted in 1838 that its teeth sit between those of Naja and the kraits, Bungarus.

Mitochondrial DNA shows that snakes from southern Thailand form a deeply separate group from those of northern Thailand, Myanmar and Guangdong. That split underlies the modern division into four species. The northern species differs from the others in its dark-edged yellow bands. It also has more teeth on the pterygoid bone, 18 to 21 against 11 or 12. Its juveniles carry 27 to 48 body bands, far fewer than the 57 to 87 of the Sunda king cobra.

Appearance

An adult king cobra is 318 to 400 centimetres long. The longest known specimen measured 585 cm, and one from Thailand reached 5.59 m. Males grow larger than females: in one Kerala sample, males reached 375 cm and 10 kilograms, females 275 cm and 5 kg. Males are also paler, especially in the breeding season. The snake is heavier in the body than most elapids and ranks among the heaviest venomous snakes.

The skin is olive green, yellow, brown or black, with pale cross-bands that run together towards the head. Colour varies across the range, from black with white stripes to a plain brownish grey. The throat is light yellow or cream. Juveniles are jet black with white, yellow or buff chevrons that point forward, and the bright marks fade with age. The tail is yellowish green above, marked with black.

The head is covered by 15 large shields, and a pair of large occipital scales sits behind them, which no true cobra has. The muzzle is rounded, the tongue black, and the big eyes show a golden iris around a round pupil. There are 17 to 19 rows of smooth scales on the neck and 15 on the body. The upper jaw holds two fangs and 3 to 5 other teeth. The hood is oval and narrower and longer than a Naja cobra's, with two black spots on the neck.

Habitat and range

The king cobra lives in dense and open forest, bamboo thickets, mangrove swamps and farmland next to forest, usually near streams. It occurs from sea level up to 2,000 metres. It probably prefers rainforest and moist forest but tolerates drier woodland and rice fields at the forest edge.

The range runs from the Terai of India and Nepal along the Himalayan foothills to Bhutan and northeast India. From there it reaches Bangladesh, Myanmar, southern China including Hong Kong and Hainan, Cambodia, Laos, Thailand and Vietnam. In the south it covers Malaysia, Singapore, Indonesia and the Philippines. In India it lives in the Eastern Ghats, the Western Ghats, the Sundarbans, the Andaman Islands and the hills of the northeast. Old records from Lahore and Palanpur in the far west were once blamed on snake charmers but are now thought to be natural.

The species is widespread but seldom seen. Singapore has 39 records between 1929 and 2010, and recent sightings include a 3 m snake in the lobby of a housing block. GBIF holds records from 23 countries, and iNaturalist has only 624 observations, which shows how rarely people meet it.

Diet and hunting

The king cobra eats mainly other snakes, including its own kind. Recorded prey includes the Indian cobra, the banded krait, rat snakes, reticulated pythons, whip snakes, keelbacks and wolf snakes. It tracks Malabar and hump-nosed pit vipers by following their scent trails. Some individuals fix on a single species of snake and refuse anything else. It also takes monitor lizards, and in Singapore one was seen swallowing a clouded monitor.

When snakes are scarce, it eats birds, other lizards and rodents. It is an apex predator and dominates every other snake except the large pythons. It hunts by day, tasting the air with its forked tongue and passing scent to the Jacobson's organ in the roof of its mouth. It bites, injects venom and swallows the prey whole, head first.

Its loose jaws let it swallow prey far wider than its own head, including rat snakes and pythons up to about 3 metres long. Now and then it wraps its body around a victim to hold it, though it is not a true constrictor. After a big meal it may not eat again for months, because its metabolism is slow.

Behaviour and social life

The king cobra is active by day, unlike most other cobras, though it has been seen at night on rare occasions. It lives alone except in the breeding season. It is a shy snake that slips away when disturbed. Wild snakes met in Singapore seemed placid until cornered, when they reared up and struck in defence.

The threat display is the most famous thing about the species. The snake raises the front third of its body, about a metre off the ground, spreads its hood, shows its fangs and hisses. It can move forward in this pose and follow an enemy for some distance, so people misjudge the safe zone. It can strike from a long way off and bite several times in one attack. Sudden movements or an object brought close set it off.

Rival males wrestle in a ritual combat, pushing each other with the front of the body and trying to press the rival down. They do not bite during these bouts. A nesting female is the exception to the snake's shyness and may attack anyone who comes near the mound. Hatchlings are alert, nervous and quick to defend themselves.

Communication and senses

Like other snakes, the king cobra reads the world mostly through scent, gathered by its flicking tongue. Its large eyes with round pupils suit a hunter that works by day. Like other snakes, it probably has no outer ear and feels vibration through its jaw and body rather than hearing airborne sound.

The king cobra's hiss is far deeper than that of other snakes. Most snakes hiss across a wide band from about 3,000 to 13,000 hertz, with a peak near 7,500 Hz. The king cobra's sound stays below 2,500 Hz, with a peak near 600 Hz, close to a human voice, so people call it a growl. Pouches on the windpipe act as resonating chambers and make the low note possible. Its prey, the rat snake, has the same pouches and makes a similar growl.

The spread hood, the raised body and the bared fangs are visual warnings meant to end an encounter without a bite. In the breeding season a male probably finds a female by following her scent trail, as other snakes do.

Reproduction and life cycle

Breeding runs from January to April, and males fight each other for females at this time. The female carries the eggs for 50 to 59 days. Between late March and late May she builds the nest, the only snake to do so. She pushes dry leaves and branches into a mound, usually at the base of a tree, up to 55 cm high and 140 cm across. The mound has several layers and usually one chamber, and the heat of the rotting leaves incubates the eggs.

A clutch holds 7 to 43 eggs, and typically 20 to 40. The eggs hatch after 66 to 105 days, and 6 to 38 young emerge from a nest. Nest temperature swings with altitude, from 13.5 to 37.4 degrees Celsius. The female lies on top of the nest for anything from two days to 77 days, and the male often stays close by. During this time she is very aggressive towards anyone who approaches.

Hatchlings measure 37.5 to 58.5 cm and weigh 9 to 38 grams. Their venom is as strong as an adult's from the first day. Females can also produce young without a male by facultative parthenogenesis. A wild king cobra lives about 20 years, and the AnAge record in captivity is 22.5 years.

Predators and threats

An adult king cobra has few natural enemies apart from large pythons. Mongooses and birds of prey take hatchlings and young snakes. Adult king cobras eat their own kind, so a small snake must fear the large ones.

The main threat is the loss of forest to logging and farmland across Southeast Asia. Poachers kill the snake for bushmeat, for its skin and for use in traditional Chinese medicine. Wildlife smugglers trade in live animals. Many people kill any king cobra they meet out of fear.

Population and conservation

The IUCN Red List has rated the king cobra as Vulnerable since 2010. Singapore also lists it as Vulnerable, and the Philippines counts it among its threatened species. No global population estimate seems to exist, because the snake is so hard to survey.

The species sits on CITES Appendix II, which controls its international trade. China and Vietnam protect it by law. In India it falls under Schedule II of the Wildlife Protection Act of 1972, and killing one can bring up to six years in prison. The Philippines bans the killing, trade and eating of the snake under its Wildlife Act. The penalty there is a fine of 20,000 pesos and up to two years in jail. The split into four species means each one now has a smaller range and probably needs its own assessment.

Relationship with humans

A bite from a king cobra is a medical emergency, and death can follow in as little as 30 minutes without treatment. One bite can deliver up to 420 milligrams of dried venom, mostly nerve toxins that stop the breathing muscles. The victim feels pain and swelling, then blurred vision, dizziness and drowsiness, and finally paralysis and collapse. In severe cases the flesh around the bite dies and a limb may need amputation. Antivenom from the Haffkine Institute and the King Institute in India and from the Thai Red Cross neutralises the venom.

Even so, the snake bites people rarely. Most bites happen when a snake is surprised, cornered or guarding a nest. The web notes put human deaths at fewer than five a year across the entire range. In India and Thailand some people treat bites with turmeric and herbs, but there is no evidence that this works.

Zoos prize the king cobra as a star of the reptile house. Female snake charmers in Myanmar perform a ritual that ends with a kiss on the top of the snake's head. Its venom is studied for drug leads, and up to 1 gram has been milked from one snake for research. India has made it the national reptile.

In culture and myth

The king cobra holds a high place in the folklore of Myanmar, Sri Lanka, Bangladesh and India. In Hindu and Buddhist tradition the great serpents, the Nagas, are guardians of treasure and water, and the king cobra is their living image. In India people believe the snake has a perfect memory. One myth says the face of a king cobra's killer stays in its eyes, and its mate reads the image and hunts the killer down. For that reason a dead cobra's head is often crushed or burned to destroy the eyes.

In Myanmar the priestess who kisses the cobra is usually tattooed with three pictograms. Members of the Pakokku clan there tattoo their upper bodies every week with ink mixed with cobra venom, which they believe protects them. No science supports the belief. In Bangkok a shrine on Rama II Road honours a female king cobra whose nest was destroyed when the road was built. A second shrine nearby honours her mate, and locals believe large king cobras still live in the scrub behind them.