Family: Boidae - Boas and Pythons
This family contains some of the largest and best known snakes in the world. Besides their geographical distribution and some anatomical differences, boas differ from pythons in that they do not lay eggs in the usual way. The embryos are retained in the body of the female in a shell-less sac until simultaneous hatching and birth, a condition known as ovoviviparity. Vestiges of hind limbs are present in these snakes, evidence of limbed ancestor. The external claw -like structures tend to be larger in males than females and are used by males of some species during courtship.

Boas and pythons comprise about 21 genera with about 66 species. Four species of boa occur in Trinidad, including the anaconda, the largest boid. Three of the species occurring  in Trinidad are also to be found in Tobago. These snakes are relatively large and their feeding on rats and mice, tend to follow human habitation. They are therefore frequently encountered and best recognized of the local snakes.  These snakes are generally placid in disposition and some species are popular pets.

Family: Colubridae - Harmless Snakes
The family is composed of what is describes as "harmless snakes". While most species are considered harmless, some have mild venom, and a few can make humans sick or even kill, because of secretion from a specialized gland. This oral gland known as Duvernoy's gland, produces enzymes and other molecules that assist the snake in subduing and digesting prey. Secretions for this gland are released during feeding and are usually not delivered during a defensive bite.

Approximately 70% of the world's snakes belong to this family, with about 300 genera and 1,600 species. Trinidad and Tobago has 33 species of colubrids representing 24 genera, grouped into three subfamilies.

Family: Typhlopidae - Blind Snakes
Small, burrowing, wormlike snakes. Like Leptotyphlopids tend to be associated with ants and termites, which they feed on. Typhlopidae includes three genera, containing about 170 species. Three species occur in Trinidad one of which also occurs in Tobago.

Family: Viperidae - Pit Vipers (Mapepires)
Vipers tend to be stout, short-tailed snakes with numerous heavily keeled scales. They have folding front fangs connected to a venom gland and many are dangerously venomous to humans. The pit vipers are so called because they possess an infrared (heat) sensing pit located between the eye and the nostril. The pit is a sense organ used to locate prey and direct feeding strikes.

There are 14 genera and about 187 species of viperidae. Two species representing two genera occur in Trinidad, none are found in Tobago.