The king cobra (Ophiophagus hannah) is the world's longest venomous snake, with a length up to 5.6 m (18.5 ft).^[1] This species is widespread throughout Southeast Asia and parts of India, and is found mostly in forested areas. The king cobra can be highly aggressive and agile, and can deliver a large quantity of highly potent venom in a single bite. It is regarded as one of the most dangerous and feared Asiatic snakes due to various factors.^[2]

Profile

The King Cobra is a large and powerful snake, averaging 3.6–4 m (12–13 feet) in length and typically weighing about 6 kg (13.2 lb). A particularly large specimen was kept captive at the London Zoo, and grew to 5.7 m (18.8 ft) before being euthanized upon the outbreak of World War II.^[3] Despite their large size, king cobras are fast and agile.

Characteristics

The skin of this snake is either olive-green, tan, or black, and it has faint, pale yellow cross bands down the length of the body. The belly is cream or pale yellow, and the scales are smooth. Juveniles are shiny black with narrow yellow bands (can be mistaken for a banded krait, but readily identified with its expanded hood). The head of a mature snake can be quite massive and bulky in appearance, though like all snakes, they can expand their jaws to swallow large prey items. It has proteroglyph dentition, meaning it has two short, fixed fangs in the front of the mouth which channel venom into the prey like hypodermic needles. The male is larger and thicker than the female. The average lifespan of a king cobra is about 20 years.

Identification

The king cobra is the sole member of genus Ophiophagus, while most other cobras are members of the genus Naja. They can be distinguished from other cobras by size and hood marks. King cobras are larger than other cobras, and the stripe on the neck is like the symbol "^" instead of a double or single eye(s) shape that may be seen in most of the other cobras. A foolproof method of identification is if on the head, clearly visible, is the presence of a pair of large scales known as occipitals, at the back of the top of the head. These are behind the usual "nine-plate" arrangement typical of colubrids and elapids, and are unique to the king cobra.

Scalation

Dorsal scales: midbody 15 rows; Ventral scales: Males 235-250, females 239-265; Tail: Subcaudal scales single or paired in each row, 83-96 in males and 77-98 in females.^[2]

Habitat

The king cobra is distributed across South Asia, Southeast Asia, and the southern areas of East Asia (southern China) where it is not common. It lives in dense highland forests,^[1][4] preferring areas dotted with lakes and streams. King cobra populations have dropped in some areas of its range because of the destruction of forests. It is listed as an Appendix II Animal within CITES.^[5]

Scalation of the King Cobra

Behavior

King cobras, like other snakes, receive chemical information ("smell") via their forked tongues, which pick up scent particles and transfer them to a special sensory receptor (Jacobson's organ) located in the roof of its mouth.^[1] When the scent of a meal is detected, the snake flicks its tongue to gauge the prey's location (the twin forks of the tongue acting in stereo); it also uses its keen eyesight (king cobras are able to detect moving prey almost 100 m [300 feet] away), intelligence^[6] and sensitivity to earth-borne vibration to track its prey.^[7] Following envenomation, the king cobra will begin to swallow its struggling prey while its toxins begin the digestion of its victim. King cobras, like all snakes, have flexible jaws. The jaw bones are connected by pliable ligaments, enabling the lower jaw bones to move independently, enabling the King cobra to swallow its prey whole. The expansion of the jaw enables the snake to swallow prey much larger than its head.^[1]

King cobras are able to hunt at all times of day, although it is rarely seen at night, leading most herpetologists to classify it as a diurnal species.^[1][8]

Defense

The king cobra can be highly aggressive if provoked.^[9] When threatened, it raises up the anterior portion of its body, extending the neck, showing the fangs and hissing loudly. (Bioacoustic analysis of the "growl" of the king cobra has shown that it differs significantly from other snakes. Generally a typical snake hiss has a broad-frequency span (~3,000 to 13,000 Hz) with a dominant frequency near 7,500 Hz, whereas the "growl" of the king cobra consists of frequencies below 2,500 Hz, with a dominant frequency near 600 Hz.)^[10] It can be easily irritated by closely approaching objects or sudden movements. The king cobra attacks rapidly, and the strike distance is about 2 m (7 feet); people can easily misjudge the safe distance. The king cobra may deliver multiple bites in a single attack, or bite and hold on.^[11] Although it is a highly dangerous snake, it, just like other snakes, prefers to escape unless it is cornered or provoked.^[9]

If a king cobra encounters a natural predator, such as the mongoose, which has some resistance to the neurotoxins,^[12] the snake generally tries to flee. If unable to do so, it forms the distinctive cobra hood and emits a hiss, sometimes with feigned closed-mouth strikes. These efforts usually prove to be very effective, especially since it is more dangerous than other mongoose prey, as well as being much too large for the small mammal to kill with ease.

Diet

The king cobra's genus name, Ophiophagus, means "snake-eater", and its diet consists primarily of other snakes, including ratsnakes, sizeable pythons and even other venomous snakes (including kraits, cobras and smaller members of its own species).^[8][13] When food is scarce, they may also feed on other small vertebrates, such as lizards, birds, and rodents. In some cases, the cobra may "constrict" its prey, such as birds and larger rodents, using its muscular body, though this is uncommon.^[1][13] After a large meal, the snake may live for many months without another one because of its slow metabolic rate.^[1] The king cobra's most common meal is the ratsnake; pursuit of this species often brings king cobras close to human settlements.

Venom

King cobra skull, lateral view, showing fangs

The venom of the king cobra consists primarily of neurotoxins, but it also contains cardiotoxic compounds.^[8] Toxic constituents are mainly proteins and polypeptides.

During a bite, venom is forced through the snake's half-inch (1.25 cm) fangs into the wound, and quickly attacks the victim's central nervous system, inducing severe pain, blurred vision, vertigo, drowsiness, and paralysis.^[14] Envenomation progresses to cardiovascular collapse, and the victim falls into a coma. Death soon follows due to respiratory failure.

In the past, the LD₅₀ of the king cobra's venom was treated as 1.6 mg/kg – 1.8 mg/kg (which was one of the least venomous elapids). However, in recent toxicology study, the LD₅₀ of Chinese king cobra venom was found to be 0.34 mg/kg^[15]. In the same test, many Naja species found in the same habitats (such as the Chinese cobra) possess larger values, thus showing that the king cobra can actually be more venomous than many other cobras based on LD50.^[15][16] The king cobra is also capable of delivering larger quantities of venom than most other snakes, injecting a 380-600 mg dose in a single bite on average. It was reported that a single bite from this species can kill an adult Asian elephant. A bite from the king cobra can cause the death of an adult human within 15 minutes,^[15] though the average death time recorded is between 30–45 minutes after envenomation.^[14][16][17] The mortality rate from a bite can be over 75%,^[8][18]depending upon treatment details. It is regarded as one of the deadliest snakes in the world.^[16][19]

There are two types of antivenom made specifically to treat king cobra envenomations. The Red Cross in Thailand manufactures one, and the Central Research Institute in India manufactures the other; however, both are made in small quantities and are not widely available.^[20] Ohanin, a protein component of the venom, causes hypolocomotion and hyperalgesia in mammals.^[21] Other components have cardiotoxic,^[22] cytotoxic and neurotoxic effects.^[23] In Thailand, a concoction of alcohol and the ground root of turmeric is ingested, which has been clinically shown to create a strong resilience against the venom of the king cobra, and other snakes with neurotoxic venom.^[24]

Reproduction

The king cobra is unusual among snakes in that the female king cobra is a very dedicated parent. She makes a nest for her eggs, scraping up leaves and other debris into a mound in which to deposit them, and remains in the nest until the young hatch.

A female usually deposits 20 to 40 eggs into the mound, which acts as an incubator. She stays with the eggs and guards the mound tenaciously, rearing up into a threat display if any large animal gets too close.^[25]

Inside the mound the eggs are incubated at a steady 28 °C (82 °F). When the eggs start to hatch, instinct causes the female to leave the nest and find prey to eat so she does not eat her young.^[26] The baby king cobras have a length of 45 to 55 centimeters (18 to 22 in). They are highly aggressive, and their venom is as deadly as that of an adult.

Other culture

In Burma, king cobras are often used by female snake charmers.^[13] The charmer is usually tattooed with three pictograms, using an ink mixed with snake venom; superstition holds that it protects the charmer from the snake.^[13] The charmer kisses the snake on the top of its head at the end of the show.^[13]

Related species

The king cobra belongs to the family Elapidae which includes other well known snakes, such as the cobra, the coral snake, the death adder and the black mamba.

Gallery

• 

  King cobra in St. Louis Zoo

• 

  A juvenile found in forest

• 

  South Indian king cobra

• 

  A male king cobra extending its hood.

Wikimedia Commons has media related to: Ophiophagus hannah

References