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Boa
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- Common names: boas, boids.
The Boidae are a family of non-venomous snakes found in the Americas, Africa, Europe, Asia and some Pacific Islands. Relatively primitive snakes, adults are medium to large in size, with females usually larger than the males. The name is derived from the Latin term bos, meaning "cow", and is based on an old myth that boas pursue cows and suckle them until they are drained to death.
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- Common names: boas, boids.
The Boidae are a family of non-venomous snakes found in the Americas, Africa, Europe, Asia and some Pacific Islands. Relatively primitive snakes, adults are medium to large in size, with females usually larger than the males. The name is derived from the Latin term bos, meaning "cow", and is based on an old myth that boas pursue cows and suckle them until they are drained to death. Two subfamilies comprising eight genera and 43 species are currently recognized.
Description
Like the pythons, boids have elongated supratemporal bones. The quadrate bones are also elongated, but not as much, while both are capable of moving freely so that when they swing sideways to their maximum extent, the distance between the hinges of the lower jaw is greatly increased.
Both families share a number of primitive characteristics. Nearly all have a relatively rigid lower jaw with a coronoid element, as well as a vestigial pelvic girdle with hind limbs that are partially visible as a pair of spurs, one on either side of the vent. In males, these anal spurs are larger and more conspicuous than in females. A long row of palatal teeth is present and most species have a functional left lung that can be up to 75% as large as the right lung.
Boids are, however, distinguished from the pythons in that none have postfrontal bones or premaxillary teeth, and that they give birth to live young. When labial pits are present, these are located between the scales as opposed to on them. Also, their geographical distributions are almost entirely mutually exclusive. In the few areas that they do coexist, the tendency is for them to occupy different habitats.
It used to be said that boas are found in the New World and pythons in the Old World, but with boid species found on Madagascar, Fiji and the Solomon Islands, this is not quite true. Instead, it seems that they have survived in evolutionarily isolated areas. After all, South America had, until a few million years ago, a distinct fauna that included marsupial and mammals. With the land bridge to North America, boids have migrated north as placental mammals and colubrids have migrated south.
Common names
The Old Tupi name for such snakes was mbói, which figures in the etymology of names like jibóia and boitatá (the Brazilian name for the mythical Giant anaconda).
Geographic range
Found in Northern, Central and South America, the Caribbean, southeastern Europe and Asia Minor, Northern, Central and East Africa, Madagascar and Reunion Island, the Arabian Peninsula, Central and southwestern Asia, India and Sri Lanka, the Moluccas and New Guinea through to Melanesia and Samoa.
Feeding
Prey is killed by a process known as constriction; after an animal has been grasped to restrain it, a number of coils are hastily wrapped around it. Then, by applying and maintaining sufficient pressure to prevent it from inhaling, the prey eventually succumbs due to asphyxiation. It has recently been suggested that the pressures produced during constriction cause cardiac arrest by interfering with blood flow, but this hypothesis has not yet been confirmed.
Larger specimens usually eat animals about the size of a house cat, but larger food items are not unknown: the diet of the common anaconda, Eunectes murinus, is known to include subadult tapirs. Prey is swallowed whole, and may take anywhere from several days or even weeks to fully digest. Despite their intimidating size and muscular power, they are generally not dangerous to humans.
Contrary to popular belief, even the larger species do not crush their prey to death; in fact, prey is not even noticeably deformed before it is swallowed. The speed with which the coils are applied is impressive and the force they exert may be significant, but death is caused by suffocation, with the victim not being able to move its ribs in order to breathe while it is being constricted.
Reproduction
Most species are ovoviviparous, with females giving birth to live young. This is in contrast to the pythons, which all lay eggs (oviparous).
Subfamilies
| Subfamily | Taxon author | Genera | Species | Common name | Geographic range |
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| Boinae | Gray, 1825 | 5 | 28 | True boas | Central and South America, Africa, Madagascar, Reunion Island, Mauritius, the Maluku Islands and New Guinea. | | Erycinae | Bonaparte, 1831 | 3 | 15 | Old World sand boas | South and southeastern Europe, Asia Minor, north, central, west and east Africa, Arabia, central and southwestern Asia, India, Sri Lanka. Also in southwestern Canada, the western United States and northwestern Mexico. | |
Type genus = Boa - Gray, 1825
Taxonomy
Pythons are sometimes classified as a subfamily of Boidae, the Pythoninae, but are in this case listed under their own family, the Pythonidae. In the same way, the Old World sand boas, the Erycinae, are also frequently listed under their own family, the Erycidae.
See also
Further reading
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