|Captive specimen at the Cincinnati Zoo|
Distribution of the king cobra
The king cobra (Ophiophagus hannah) is the world's longest venomous snake, with a length up to 18.5 to 18.8 ft (5.64 to 5.73 m). This species, which preys chiefly on other snakes, is found predominantly in forests from India through Southeast Asia. Despite the word "cobra" in its name, this snake is not a member of Naja ("true cobras") but belongs to its own genus. The king cobra is considered to be a dangerous snake and has a fearsome reputation in its range, although it typically avoids confrontation with humans if possible. It is also considered culturally significant and has many superstitions around it.
The king cobra averages at 3 to 4 m (9.8 to 13.1 ft) in length and typically weighs about 6 kg (13 lb). The longest known specimen was kept captive at the London Zoo, and grew to around 18.5 to 18.8 ft (5.64 to 5.73 m) before being euthanised upon the outbreak of World War II. The heaviest wild specimen was caught at Royal Island Club in Singapore in 1951, which weighed 12 kilograms (26 lb) and measured 4.8 m (16 ft), though an even heavier captive specimen was kept at New York Zoological Park and was measured as 12.7 kilograms (28 lb) at 4.4 m (14 ft) long in 1972. The length and mass of the snakes highly depend on their localities and some other factors. Despite their large sizes, typical king cobras are fast and agile. Some viper species, such as Eastern diamondback rattlesnakes and Gaboon vipers, often much shorter in length but bulkier in build, rival the King cobra in average weight and reportedly best them in maximum weight.
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 expandable 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 wild king cobra is about 20 years.
The dorsal scales along the centre of the king cobra's body have 15 rows. Males have 235 to 250 ventral scales, while females have 239 to 265. The subcaudal scales are single or paired in each row, numbering 83 to 96 in males and 77 to 98 in females.
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. King cobras are generally larger than other cobras, and the stripe on the neck is a chevron instead of a double or single eye shape that may be seen in most of the other Asian cobras. Moreover, the hood of the king cobra is narrower and longer. 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.
Distribution and habitat
The king cobra is distributed across the Indian Subcontinent, Southeast Asia, and the southern areas of East Asia (where it is not common). It lives in dense highland forests, 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.
A king cobra, like other snakes, receives chemical information via its forked tongue, which picks up scent particles and transfers them to a special sensory receptor (Jacobson's organ) located in the roof of its mouth. This is akin to the human sense of smell. 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 [330 feet] away), intelligence, and sensitivity to earth-borne vibration to track its prey.
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. This allows the king cobra to swallow its prey whole, as well as letting it swallow prey much larger than its head.
The king cobra's generic name, Ophiophagus is a Greek-derived word which means "snake-eater", and its diet consists primarily of other snakes, including ratsnakes, small pythons and even other venomous snakes such as various members of the true cobras (of the genus Naja), and even the much more venomous krait. 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. After a large meal, the snake may live for many months without another one because of its slow metabolic rate. The king cobra's most common meal is the ratsnake; pursuit of this species often brings king cobras close to human settlements.
When concerned, it rears up the anterior portion (usually one-third) of its body when extending the neck, showing the fangs and hissing loudly. It can be easily irritated by closely approaching objects or sudden movements. When raising its body, the king cobra can still move forward to strike with a long distance  and people may misjudge the safe zone. This snake may deliver multiple bites in a single attack  but adults are known to bite and hold on. It is secretive and tends to inhabit less-populated forested regions and dense jungle, and thus many victims bitten by king cobras are actually snake charmers.
Some scientists believe that the temperament of this species has been grossly exaggerated. In most of the local encounters with live, wild king cobras, the snakes appear to be of rather placid disposition, and they usually end up being killed or subdued with hardly any hysterics. These support the view that wild king cobras generally have a mild temperament, and despite their frequent occurrence in disturbed and built-up areas, are adept at avoiding humans. Naturalist Michael Wilmer Forbes Tweedie felt that "this notion is based on the general tendency to dramatise all attributes of snakes with little regard for the truth about them. A moment’s reflection shows that this must be so, for the species is not uncommon, even in populated areas, and consciously or unconsciously, people must encounter king cobras quite frequently. If the snake were really habitually aggressive records of its bite would be frequent; as it is they are extremely rare."
If a king cobra encounters a natural predator, such as the mongoose, which has resistance to the neurotoxins, 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 much more dangerous than other mongoose prey, as well as being much too large for the small mammal to kill with ease.
A good defence against a cobra for anyone who accidentally encounters this snake is to slowly remove a shirt or hat and toss it to the ground while backing away.
The growling hiss
The hiss of the king cobra is a much lower pitch than many other snakes and many people thus liken its call to a "growl" rather than a hiss. While the hisses of most snakes are of a broad-frequency span ranging from roughly 3,000 to 13,000 Hz with a dominant frequency near 7,500 Hz, king cobra growls consist solely of frequencies below 2,500 Hz, with a dominant frequency near 600 Hz, a much lower sounding frequency closer to that of a human voice. Comparative anatomical morphometric analysis has led to a discovery of tracheal diverticula that function as low-frequency resonating chambers in king cobra and its prey, the mangrove rat snake, both of which can make similar growls.
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, for roughly 60 to 90 days. 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. The baby king cobras, with an average length of 45 to 55 cm (18 to 22 in), have venom which is as potent as that of the adults. They may be brightly marked, but these colours often fade as they mature. They are alert and nervous, being highly aggressive if disturbed.
The venom of the king cobra consists primarily of neurotoxins, but it also contains some other compounds. Similar to other venomous creatures, toxic constituents inside the venom are mainly proteins and polypeptides.
Its venom toxicity is 1.7—1.80 mg/kg SC, 1.31 mg/kg for IV and 1.644 mg/kg for IP. The mean LD50 value of five wild caught king cobras in Southeast Asia was determined as 1.93 mg/kg SC in another study. These values are considerably lower than many elapids and more in line with some pit-vipers.
This species is capable of delivering a fatal bite and the victim may receive a large quantity of venom with a dose anywhere from 200 to 500 mg  or even up to 7 ml. Engelmann and Obst (1981) list the average venom yield at 420 mg (dry weight). Accordingly, large quantities of antivenom may be needed to reverse the progression of symptoms developed if bitten by a king cobra.
During a bite, venom is forced through the snake's 1.25 to 1.5 cm (0.492 to 0.59 in) fangs into the wound, and the toxins begin to attack the victim's central nervous system. Symptoms may include severe pain, blurred vision, vertigo, drowsiness, and paralysis. If the envenomation is serious, it progresses to cardiovascular collapse, and the victim falls into a coma. Death soon follows due to respiratory failure. Moreover, envenomation from king cobras is clinically known to cause renal failure as observed from some snakebite precedents of this species but this is uncommon.
Not all king cobra bites result in envenomation. In the case of king cobras, the percentage of blank bites may be quite high, >50% in one series of 47 cases from Malaysia. In another series, 1 of 3 snake charmers bitten by large king cobras showed no signs of envenomation, while the other two showed only minor symptoms of envenomation. King cobra bites often involved non-fatal amounts of venom The general mortality rate of untreated bites is 28%. However, should a king cobra seriously envenomate with a full dose of venom, the untreated mortality rate can rise up to 50-60% according to the University of Adelaide Department of Toxicology. This however is rare due to the fact that over 50% of king cobra bites are dry bites. Bites from a king cobra may result in a rapid fatality  which can be as early as 30 minutes after the envenomation, although a 12-hour case is also on the record. Proper and immediate treatments are critical to avoid the occurrence of death. Successful precedents include a client who recovered and was discharged in 10 days after being treated by accurate anti-venom and inpatient care.
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, while available to order, are not widely stocked. Ohanin, a protein component of the venom, causes hypolocomotion and hyperalgesia in mammals. Other components have cardiotoxic, cytotoxic and neurotoxic effects. 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.
The haditoxin in the king cobra venom was discovered by Singaporean scientists to be structurally unique and can have unique pharmacological properties. Biochemical studies confirmed it existed as a noncovalent dimer species in solution. Its structural similarity to short-chain α-neurotoxins and κ-neurotoxins notwithstanding, haditoxin exhibited unique blockade of α7-nAChRs (IC50 180 nM), which is recognized by neither short-chain α-neurotoxins nor κ-neurotoxins.
In Burma, king cobras are often used by female snake charmers. 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. The charmer kisses the snake on the top of its head at the end of the show.
In the Indian Subcontinent, the king cobra is believed to possess exceptional memory. According to a myth, the picture of the killer of a king cobra stays in the eyes of the snake, which is later picked up by the partner and is used to hunt down the killer for revenge. Because of this myth, whenever a cobra is killed, especially in India, the head is either crushed or burned to damage the eyes completely.
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