B. cavernum has a head and body length of 65-118 mm, the tail is vestigial and concealed in the base of the interfemoral membrane, and forearm length 51-69 mm. Adult weights are about 45 grams. Coloration is ivory yellow tipped with sepia on the upperparts, but there are patches on the neck, shoulders and sides where the hairs do not have the sepia tips. The underparts are usually brown.

The muzzle narrows toward the tip and there is a v-shaped groove in the lower lip which has tiny tubercles along the margin. B. cavernum has a vestigial nose leaf, and small, separate ears. The interfemoral membrane is well developed. Molars are broad and well-ridged. This bat has a shrill, rasping call.

B. cavernum is an opportunistic feeder, consuming many kinds of fruits and flowers, pollen, nectar and insect. They may be found roosting in either well lit or dim sites such as caves, buildings and wells, emerging rather late in the evening as they go out to forage. They are fairly aggressive and sometimes hit and bite one another, especially while feeding.

Colonies of B. cavernum are usually quite large, with as many as 10,000 individuals estimated in one roost in Cuba. Adults, subadults and young of both sexes are all found within one colony, with relatively few barren females.

B. cavernum is found in Puerto Rico, Virgin Isls, and throughout Lesser Antilles south to St. Vincent and Barbados.