Mona Boa

views updated

Mona Boa

Epicrates monensis monensis

ListedFebruary 3, 1978
FamilyBoidae (Boa)
DescriptionNonvenomous light brown snake with dark brown markings.
HabitatMona Island; limestone outcroppings and scrub vegetation.
FoodCarnivorous; small mammals and reptiles.
ReproductionLive-bearer; eight to 30 young.
ThreatsLimited distribution, low numbers.
RangePuerto Rico


The Mona boa, Epicrates monensis monensis, is a nonvenomous snake about 3.3 ft (1 m) in length when fully grown. Adults are light brown above with 44 dark brown markings. The underside is beige with a few scattered spots. Immature snakes are a yellow-brown with two rows of dark brown spots extending from the head to the end of the tail.


The Mona boa is nocturnal and secretive, and Mona Island's rugged terrain and spiny plants provide an abundance of hiding places. Most captured specimens have been immature snakes, surprised in the open or taken from tree branches. The snake has not been studied in the wild. Scientists surmise that it stalks small mammals and reptiles and have observed it to capture rats, mice, and anoles. It is thought to prey upon bats, an important part of the diet of other boas. Members of the genus Epicrates, being ovoviviparous, bear their young alive, producing eight to 30 at a time.


Mona Island is a rocky limestone island situated halfway between Puerto Rico and Hispaniola. Its total surface area is about 2,226 acres (900 hectares). The island is characterized by a flat central plateau (Mona Plateau) surrounded by steep, sometimes sheer, cliffs. Much of the plateau is covered by out-crops of bedrock limestone, interspersed with tracts of dry scrub, consisting of dwarf trees and shrubs. Dominant plants of this community are gumbo-limbo, wild fig, white cedar, and poison tree. Along the coasts, organ-pipe cacti become dominant, in places forming dense thickets. Mean annual rainfall is 31 in (79 cm).


The Mona boa is endemic to Mona Island and was probably once found throughout the island. The genus Epicrates is distributed throughout Central America, northern South America, and the Greater Antilles.

The Mona boa has always been uncommon and was considered extinct until the 1970s when visitors to the island incidentally collected the snake. One specimen was kept as a pet until shown to a herpetologist, who recognized its importance. The size and status of the boa population on the island is largely unknown. Some scientists have suggested that the snake is more common than it seems because of its reclusive habits.


The decision to add the Mona boa to the list of endangered and threatened species was made as a precaution to protect this uncommon snake until further research is able to determine its relative abundance and evaluate potential threats. Predation by feral cats that were introduced to the island is considered a distinct possibility. A program to trap and remove feral cats was initiated in 1978 and continues. Other introduced animals, such as goats and pigs, have modified portions of the island's plant community. Scientists have also noted a decline in the island's bat population. All of these factors will be considered in the research strategy.

Conservation and Recovery

The Puerto Rico Department of Natural Resources took over management of Mona Island in 1973. In 1977, a special Ranger Corps was created to enforce conservation laws, monitor wildlife population levels, and educate visitors to the island. Seven rangers and a resident biologist now live on the island year-round and are charged with protecting the boa and other endemic fauna. The entire island has been designated as critical habitat for the Mona boa.


U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
1875 Century Blvd., Suite 200
Atlanta, Georgia 30345

U. S. Fish and Wildlife Service
Boquerón Ecological Services Field Office
P. O. Box 491
Boquerón, Puerto Rico 00622-0491
Telephone: (787) 851-7297
Fax: (787) 851-7440


Campbell, H. W. 1978. "Observations of a Captive Mona Island Boa." Bulletin of the Maryland Herpetological Society 14 (2): 98-99.

Rivero, J. A. 1978. Los Anfibios y Reptiles de Puerto Rico. Editorial Universitaria, Universidad de Puerto Rico, San Juan.

Rivero, J. A., et al. 1982. "Cinco Nuevos Ejemplares del Culebron de la Mona Epicrates monensis monensis. " Caribbean Journal of Science 17: 1-4.

U. S. Fish and Wildlife Service. 1984. "Mona Boa Recovery Plan." U. S. Fish and Wildlife Service, Atlanta.