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To many people, the cobra is the quintessential venomous snake. Cobras discussed in this article include species in the genus Naja and other similar venomous snakes, such as Ophiophagus hannah (king cobra), Hemachatus haemachatus (ringhals), Walterinnesia aegyptia (desert black snake), Boulengerina species (water cobras), and Pseudohaje species (tree cobras).

Most cobras are large snakes, 1.2-2.5 m in length. The king cobra, which may reach 5.2 m, is the largest venomous snake in the world. Cobras live throughout most of Africa and southern Asia. Their habitats vary, and some species adapt readily to life in cultivated areas and around villages.

When encountered, cobras usually try to escape but occasionally defend themselves boldly and may appear aggressive. Most of these snakes elevate the head and spread the neck as a threat gesture. However, a number of other snakes, venomous and nonvenomous, use this defense as well.

Most snakebites are inflicted on body extremities. Because cobras are popular as show snakes, bites on the hands and fingers are common.

By far, rural agricultural workers and other people in Asia and Africa receive most bites while working outdoors without protective footwear or when cutting tall grass with a hand blade. In North America and Europe, captive snakes usually cause bites, zookeepers and amateur collectors being at greatest risk.

Not all snakebites result in envenomation. In the case of cobras, the percentage of blank bites may be quite high, 45% 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.

In addition to biting, some cobra species have a unique defense; they eject or spit jets of venom toward an enemy, usually at the eyes. The fangs of these species are specially modified with the discharge orifice on the anterior face rather than at the tip. The effective discharge range of a large snake is at least 3 m. The ringhals and certain African species of Naja are the most effective spitters, but the spitting behavior also is observed among some Asian Naja species.

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Boa , name for live-bearing constrictor snakes of the family Boidae, found mostly in the Americas. This family, which also comprises the egg-laying pythons of the Old World, includes the largest of all snakes, as well as many smaller ones. Members of the boa family have two functional lungs instead of one, as is found in other snakes, and vestiges of hind limbs; these primitive characteristics are indicative of their relationship to lizards. Each of the two tiny, internal leg bones ends in an external horny claw; the claws are much more prominent in males than in females. Boas capture their prey by striking with their teeth and simultaneously throwing their bodies in a coil around the victim. They then squeeze the animal so that, unable to expand its rib cage, it suffocates. Like other snakes, boas swallow the prey whole. Over 30 boa species are found from Mexico to South America, with the greatest variey in the tropics, and two in the United States. Boas may be terrestrial, arboreal, or burrowing. Some are brightly colored, like the green and white emerald tree boa of the tropics (Boa canina), or iridescent, like the wide-ranging rainbow boa (Epicrates cenchris). Best known is the boa constrictor (Constrictor constrictor), which lives in a variety of terrestrial habitats from S Mexico to central Argentina. It averages 6 to 9 ft (1.8–2.7 m) in length, occasionally reaching 14 ft (4.3 m), and has dark brown diamond markings on a lighter background. The South American anaconda (Eunectes murinus) is a semiaquatic boa that inhabits swamps and river shallows, catching animals that come to drink. The longest member of the boa family and the thickest of all snakes, it may reach 25 ft (7.9 m) in length and 3 ft (90 cm) in girth. The rubber boa (Charina bottae) is found in moist regions of the far W United States and extreme SW Canada. It is a burrower, about 18 in. (46 cm) long, with a narrow, blunt head, broad, blunt tail, and silver-green skin. It feeds chiefly on lizards and rodents. The rosy boa (Lichanura roseofusca) is found in chaparral in the SW United States and N Mexico; it grows about 3 ft (90 cm) long. It has large, dark brown spots on a lighter background. Several species of sand boa (Eryx) are distributed from India and central Asia to N Africa and SE Europe; all are burrowers in sand. There are also several boa species on Madagascar and several on Pacific islands. Boas are classified in the phylum Chordata, subphylum Vertebrata, class Reptilia, order Squamata, family Boidae.

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