Boa Constrictor

Boas are a type of snake that is a member of the Boidae family. Boas are basal snakes that are "primitive" in evolutionary terms (i.e. less derived). They are constrictors and give birth to live young. They have anal spurs, a pair of claws on each side of the cloaca, which are vestiges of legs. Boas are named after cows (bos) because of the old myth that boa snakes pursue cows and suckle them until they are drained to death. 

Boas have two subfamilies: Boinae or true boas and Erycinae or sand boas. Pythons are sometimes classified as a subfamily of Boidae, but are frequently listed under their own family, Pythonidae. 

Boinae 

True boas are medium-sized to large snakes. Females are usually larger than their male counterparts. Boas contain many subspecies based on locality. They include Columbian, Suriname, Bolivian, Peruvian, Hog Island, Long Tail Peruvian, Argentine and more. The boas from the Amazon basin are the most colorful possessing bright cherry red tails. It used to be said that boas were New World Snakes and pythons were Old World Snakes, but, with boas found on Madagascar and the Solomon Islands, this is not quite true. Instead, it is possible that boas have survived in evolutionarily isolated areas. South America, until a few million years ago, had a distinct fauna that included marsupial mammals; with the land bridge to North America, boas have migrated north as placental mammals and colubrids (for example) have migrated south. 

Constriction is a method used by various snake species to kill their prey. The snake initially bites its prey and holds on, pulling the prey into its coils or, in the case of very large prey, pulling itself onto the prey. The snake will then wrap one or two coils around the prey, typically the prey's chest. Contrary to myth, the snake does not crush the prey, or even break its bones, but instead squeezes, tightening its grip every time the prey exhales and holding firm, until the prey can no longer draw in air. The prey asphyxiates, and the snake then begins to feed. The entire process is surprisingly rapid, with prey often succumbing as quickly as a minute after being struck. 

Certain groups of snakes have stereotyped patterns of constriction, including the number of coils they use and the orientation of the coils. Also, there is controversy about how much role restriction of circulation plays in subduing prey. 

The Red-tailed Boa, Boa constrictor, is a species of boa, the largest member of the family Boidae, with the largest recorded specimen being over 18 feet long. It has an interesting pattern of brown and black with a red tail. It does well in captivity and tames easily and is a common sight in zoos and homes. 

The common name "boa constrictor" can also be used to refer to any of the four species in the genus Boa as all are constrictors — that is, they kill their prey by constriction. 

Tree boa

While there are numerous arboreal boas, Tree boa most often refers to the genus Corallus. This genus contains eight species, though taxonomic re-arrangements are common. All species are long, slightly laterally flattened, with thin bodies and large heads. They typically have large eyes (though this is less pronounced in large species like the Emerald tree boa, Corallus caninus), boxy heads, and highly elongated anterior teeth, which are often several times the length one would expect for a snake of their size. These huge teeth can penetrate layers of feathers to get a firm grip on birds, their primary prey. All members of the genus are highly nocturnal, and have large numbers of very pronounced heat-sensing pits along their lips. 

Two species are frequently imported as display animals, the Amazon tree boa (Corallus hortulanus) and the Emerald tree boa (Corallus caninus). Pet is not a term one would apply to these species, as most, if not all, have a highly aggressive demeanor, and will strike readily. Their stunning coloration makes them popular, but their specialized habitat and feeding make them suitable only for advanced keepers.