Elapid Snakes
Elapid Snakes
Elapid snakes are extremely venomous snakes such as cobras, mambas, kraits, tiger snakes, and coral snakes in the family Elapidae. This family, which includes about 300 species, is usually divided into two subfamilies—the Elapinae and the Hydrophiinae. The Elapinae includes coral snakes, cobras, mambas, and terrestrial kraits, while the Hydrophiinae includes the sea snakes, sea kraits, and Australo-Papuan elapids. Elapid snakes have a wide distribution from warm temperate climates to tropical climates, and are found on all continents except Antarctica.
Biology of elapid snakes
Elapid snakes have teeth on the front part of the upper jaw that are modified as paired fangs to inject venom into their victims. The fangs deliver the venom in much the same way that a hypodermic syringe delivers a drug, i.e., as a subcutaneous injection under pressure through narrow tubes. The fangs of elapid snakes are permanently erect, and when the mouth is closed they are enclosed within a pocket in the outer lip, outside of the lower mandible. At any one time, only two fanged teeth are functionally capable of delivering venom. However, there are a series of smaller, developing fangs available as replacements, should the primary ones be damaged, lost during use, or shed. Elapid snakes bite to subdue their prey, and when attempting to protect themselves from their own predators.
Three species of elapid snakes have the ability to deliver their venom through the air, by “spitting” rather accurately towards the eyes of a predator, in some species to a distance of up to 9.8 ft (3 m). This is primarily a defensive behavior, rather than one used for hunting. The spitting cobra (Hemachatus hemachatus) of South Africa is especially accurate, and can propel its venom as far as 6.5 ft (about 2 m). Other spitting cobras are the African black-necked cobra (Naja nigricollis) and a subspecies of the Asian cobra (Naja naja sputatrix). If the venom of a spitting cobra is not quickly washed from the eyes, blindness could occur.
When cobras feel threatened, they will raise the front of their body above the ground, and face the danger. At the same time, cobras use extensible neck ribs to spread their so-called “hood,” as a further warning to the potential predator. The erect stance and spread hood of cobras is a warning display, used to caution predators about meddling with a dangerous snake.
Most elapid snakes are oviparous, meaning they lay eggs, which, after a period of incubation, hatch into young that are small replicas of the adult animals. Some species of elapid snakes, most commonly cobras, guard their eggs until they hatch. Some species, including the spitting cobra, are ovoviviparous, meaning the eggs are retained within the body of the female until they hatch, so that live snakes are born. Australian snakes in the genus Denisonia are viviparous, meaning true eggs are never formed by the female, and live young are born.
The greatest recorded longevity of an elapid snake was for the forest cobra (Naja melanoleuca ), which lived 29 years in captivity.
Fish-eating sea snakes can reach a body length of 9.2 ft (2.8 m) and occur in tropical waters in eastern Africa and the Red Sea, Asia, Australia, and many Pacific islands. Sea snakes have very toxic venom, but most species are not aggressive, and they rarely bite humans. Sea snakes have a laterally compressed, paddle-shaped tail, well adaptive to swimming, and most species are ovoviviparous. Some species of sea snakes occasionally form mass aggregations, probably for breeding, and such gatherings have been estimated to contain several million individuals.
One especially seafaring species, the pelagic sea snake (Pelamis platurus ), ranges from the east coast of Africa, through the Indo-Pacific region, and has even crossed the Pacific Ocean, occurring in tropical waters of western South America. Sea snakes are probably the basis of folk legends about sea serpents, although the living sea snakes do not closely resemble the fantastically large and aggressive serpents of folk lore.
Species of elapid snakes
Perhaps the world’s most famous species of elapid snake is a subspecies of the Asian cobra (Naja naja ) known as the Indian cobra (N. n. naja ), which is the serpent that is most often used by snake charmers. Often, the cobra emerges from the urn or sack in which it is kept, and then assumes its warning stance of an erect fore-body and spread hood. In addition, the serpent “dances” sinuously in response to the movements of the flute, as it is waved about in front of the cobra. Actually, the cobra is deaf to most of the music played by the charmer’s flute—it is only responding to the movement of the instrument.
The world’s longest venomous snake is the king cobra (Ophiophagus hannah ), which can attain a length of 18 ft (5.5 m). This impressive but uncommon snake is found in India and Southeast Asia, and it feeds primarily on other species of snakes.
The mambas are four species of African elapids, of which the black mamba (Dendroapsis polylepis ) is most feared, because it is relatively common and many people are bitten each year. This snake can grow to a length of 13 ft (4 m), and is probably the most swiftly moving of all snakes.
Elapid snakes are relatively diverse and abundant in Australia, where species of venomous snakes actually outnumber nonvenomous snakes by four to one. The largest, most dangerous species is the taipan (Oxyuranus scutellatus ), an uncommon, aggressive, tropical species that can reach a length of 11.5 ft (3.5 m). However, several species of tiger snakes (Notechis scutatus and N. ater ) are more common and widespread, and have particularly deadly venom. The death adders (Acanthophis antarcticus and A. pyrrhus ) are viper-like elapids that are relatively common and widespread.
American elapids are represented by about 40 species of coral snakes, in the genera Micrurus and Micruroides. These snakes have extremely potent venom. However, coral snakes are not very aggressive, possessing relatively short fangs and a small mouth, so they cannot easily bite most parts of the human body, with fingers and toes being notable exceptions. Coral snakes are brightly colored with rings of black, red, and yellow.
The most widespread species in North America is the eastern coral snake (Micrurus fulvius fulvius ), occurring widely in the southeastern United States from southern North Carolina to eastern Louisiana. The eastern coral snake likes to burrow, and is not often seen unless it is specifically looked for. This snake feeds almost entirely on reptiles, with frogs and small mammals also occasional prey. The eastern coral snake has brightly colored rings of red, yellow, and black on its body. These are a warning or aposematic coloration, intended to alert predators to the dangers of messing with this potentially dangerous, venomous snake.
However, in the coral snake the red and yellow rings occur adjacent to each other, unlike similarly colored but nonpoisonous species such as the scarlet kingsnake (Lampropeltis triangulum ) and the scarlet snake (Cemophora coccinea ). These latter snakes are mimics of the coral snake, which share aspects of its coloration to gain some measure of protection from predators. A folk saying was developed to help people remember the important differences in coloration between the coral snake and its harmless mimics: “Red touch yellow, dangerous fellow. Red touch black, venom lack.” The Texas coral snake (Micrurus fulvius tenere ) occurs in parts of the central and southwestern United States and Mexico.
Elapid snakes and humans
Species of elapid snakes are among the most feared of the serpents, and each year many people die after being bitten by these animals. This is especially true of certain tropical countries, particularly in India and tropical Asia, and in parts of Africa. For example, thousands of fatal snake bites occur each year in India alone. Wherever elapids and other poisonous snakes occur, there is a tangible risk of snake bite.
However, in many places the magnitude of the risks of a snake bite are grossly overestimated by people. Except in the case of unusually aggressive species of snakes, it is extremely unlikely that a careful person will be bitten by a venomous snake, even where these animals are abundant. In the greater scheme of things, snake bites may be deadly, but in terms of actual risk, snakes are not usually very dangerous. This is especially true in North America, but somewhat less so in some tropical countries.
However, any bite by a poisonous snake should be treated as a medical emergency. First-aid procedures in the field can involve the use of a constriction band to slow the absorption of the venom into the general circulation, and perhaps the use of incision and suction to remove some of the poison. Antivenins are also available for the venoms of many species of poisonous
Key Terms
Antivenin— An antitoxin that counteracts a specific venom, or a group of similar venoms. Antivenins are available for most types of snake venoms.
Aposematic— Refers to a bright coloration of an animal, intended to draw the notice of a potential predator, and to warn of the dangers of toxicity or foul taste.
snakes. Antivenins are commercially prepared serums that serve as antidotes to snake venoms if they are administered in time.
It is regrettable that so many poisonous snakes— and harmless snakes—are killed each year by people with fears that are essentially misguided and overblown. Snakes are a valuable component of natural ecosystems. Moreover, many species of snakes provide humans with useful services, for example, by preying on rodents that can potentially cause great damage in agriculture or serve as the vectors of human diseases.
Resources
BOOKS
Halliday, T.R., and K. Adler. The New Encyclopedia of Reptiles and Amphibians. New York: Oxford University Press, 2002.
Mattison, C. Snakes of the World. New York: Facts on File, 1999.
O’shea, Mark. Venomous Snakes of the World. Princeton, NJ: Princeton University Press, 2005.
Zug, George R., Laurie J. Vitt, and Janalee P. Caldwell. Herpetology: An Introductory Biology of Amphibians and Reptiles. 2nd ed. New York: Academic Press, 2001.
Zweifel, R.G., H.G. Cogger, and D. Kirshner, eds. Encyclopedia of Reptiles and Amphibians. 2nd ed. Academic Press, 1998.
Bill Freedman