Recent molecular work by Noonan and Chippendale (2006 Molecular Phylogenetics and Evolution 40:347-358) using mDNA and nuclear genes suggest that snakes traditionally placed in this family form clades that correlate with geography. This suggests that boids are restricted to the Western Hemisphere, ranging from Mexico southward into Central and South America, and they occur in the West Indies. There are four genera with about 20 species. Boas are viviparous giving birth to live young. Boas are also constrictors that kill their prey by wrapping coils of their body around the prey and applying enough pressure to stop the flow of blood to the heart, and greatly reduce breathing. They fed on vertebrates. In size they range from the huge anaconda, possibly the largest living snake (if not the longest, certainly the species with the greatest weight) which can attain a length of more than 8 m, to the small Epicrates exsul which has a maximum size of 0.8 m. Previously many more genera and species were placed in this family including the pythons, molecular studies suggest that the previous arrangements contained several different ancestral lineages. Thomas Barbour (1928 Amphibians & Reptiles) described boas catching prey.
"They maneuver the body so that the forward part lies free and is not coiled upon itself. They seize with a lightning-like thrust and, soon as the teeth have sunk into the victim, contract the muscular body till both snake and prey are moved together. Coil after coil is then thrown about the victim, which soon suffocates."
Dumeril's Boa, Acrantophis dumerili Jan, 1860. Photograph of a captive. Dumeril's Boa is a noctural, terrestrial snake of the drier regions of Madagascar. It appears to spend the day in leaf litter and hunt rodents at night. Adults reach at least 1.8 m and stories of them reaching 4 m are common. Given the results of Noonan and Chippendale (2006) it seems likely the Madagascar boas will be removed from the family Boidae placed in their own family.
The Common Boa, Boa constrictor (Linnaeus, 1758).Top two photos are animals photographed on Trinidad, the third photo is a captive raised adult from an unknown source, the fourth photo is an animal photographed in Cayo, Belize; and the fifth photo is a captive animal. The Common Boa ranges from northern Mexico through Central America, and southward in South America to Bolivia, Uruguay, and Argentina. It also occurs on islands in the Lesser Antilles; and on islands off the coasts of its mainland range. Currently, there is a breeding population of Boa constrictor in southern Florida that is the result of released pets. There have been at least eight subspecies named, and it is unlikely that the names correspond with actual genetic variation or ancestry. Thus, until the genetics are worked out it is best to ignore subspecific names. Because this animal is exceptionally popular in the pet trade, a variety of names have been applied to various populations and color morphs. There may be several species currently recognized under the name Boa constrictor, considering its huge distribution and the fact that individuals can have 55-88 scale rows at midbody. Maximum size for the boa is probably in the 4-5 m range. Boas, anacondas, and pythons have been long confused in the older literature and their sizes have often been confused and exaggerated. Boas have relatively short tails. The Common Boa is terrestrial and arboreal and it can be active at anytime of day or night. Habitats used range from desert scrub to primary rainforest, and habitats severely altered by humans can also be used. The Boa feeds on vertebrates, killing them with constricting coils of its body. Young are frequently born during the wet season, and litter size is usually in the 12-50 range.
The Emerald Treeboa, Corallus caninus (Linnaeus, 1758). Photograph of a captive specimen. The Emerald Treeboa is widely distributed in lowland South America from Venezuela and the Guianas southward into the Amazon Basin of Bolivia and Brazil.
Ruschenberger's Treeboa, Corallus ruschenbergii (Cope, 1876). Photographed in Trinidad's Arima Valley. The species ranges from southwest Costa Rica to Panama and Colombia eastward to Venezuela and Guiana Shield, and the continental islands of Trinidad and Tobago. This species has been long confused with Corallus cookii that is endemic to St. Vincent and nearby islands in the West Indies. Adults can reach more than 2 m in total length, with a tail that can be 26% of the body length. It is a nocturnal species active in trees, and sometimes coming to the ground. Food includes birds, bats, and lizards. Females may have litters of 20-30 neonates.
Grenadine Tree Boa, Corallus grenadensis (Barbour, ) is a relativel small and gracile member of the genus Corallus. It is widespread in the Grendine Bank and the animals shown here were photographed in Grenada and Carriacou. The Grenadine Tree Boa is highly polymorphic and it comes in a variety of color and pattern phases. Adults reach 1.6 m. Neonates and snakes under a meter tend to feed on Anolis, larger individuals switch their diet to rodents and other mammals. They are highly arboreal amd nocturnal. The local people refer to them as the "serpent." For more on these intersting snakes, see: Henderson, R. W. 2002. Neotropical Treeboas. Natural History of the Corallus hortulanus Complex. Malabar: Krieger Publishing.
Caicos Island Boa, Epicrates chrysogaster (Cope, 1871). Photograph of a captive animal probably from the Caicos Islands. Inhabits the Bahamas, Turks, and Caicos Islands. Maximum adult size to 1.3 m. Juveniles probably feed on frogs and lizards while adults feed on birds and small mammals.
The Rainbow Boa, Epicrates cenchria (Linnaeus, 1758). Photograph of a juvenile (first 3 photos)from Trinidad's Arima Valley. Botton photo a Brazilian Rainbow Boa, captive bred. Rainbow boas are widespread ranging from Costa Rica southward to Panama and into South America east of the Andes as far south as Paraguay, Argentina, and Bolivia. Adults reach 1.7 m in total length. Habitats used include forest-edge and savanna as well as agroecosystems. They climb well, but are often found on the ground. Food includes a variety of vertebrates ranging from frogs, birds, and mammals.
The Anaconda, Eunectes murinus (Linnaeus, 1758). Photographs of a juvenile from Trinidad (top two) and a zoo specimen. The Anaconda is perhaps the largest snake in terms of mass, but it is probably not the longest snake. The genus Eunectes is the sister to the South American Epicrates (the West Indies Epicrates form a distinct clade). The maximum size of this snake is often given as 37.5 feet , this is an error. Rarely does the species exceed 25 feet (see Murphy and Henderson, 1997 Tales of Giant Snakes, Krieger Publishing for a discussion). Anacondas feed on a variety of vertebrates which are pulled into the water (or caught in the water), constricted, and swallowed.
