Aruba Island rattlesnake  (Crotalus unicolor)

Classified as Critically Endangered (CR) on the IUCN Red List 2007 (1), and listed on Appendix III of CITES (3).

The Aruba Island rattlesnake is one of the rarest rattlesnakes in the world (2). Its short and stocky looking body has an overall brown colour and a lighter brown tail tip and its scaly skin has distinctive pink, blue and brown diamond shaped markings (4). Males and females are similar in appearance though males are larger in size. The tail creates the rattling noise that gives this snake its name. This species belongs to the family of vipers, and like other vipers it has a V shaped head, and venomous long hollow fangs which fold against the roof of the mouth when they are not being used (5).

As its name suggests, this species is found on Aruba Island, located off the coast of Venezuela. The island has an area of only 12 square kilometres (2).

Aruba Island is volcanic and the environment is rocky, dry and covered with cactus scrub and thorny plants (4).

This snake is nocturnal in the warmer months, though during the rest of the year it is active in the early morning and late afternoon. It feeds on small rodents, birds, and lizards, locating them with a pair of heat sensitive pits that are found between the eyes and nostrils (5). Like other rattlesnakes it injects its prey with a lethal cocktail of chemicals which kills the prey and begins to digest it from the inside (2). The snake then swallows the prey (5). In the wild, the Aruba Island rattlesnake may only eat a few times a year (2).

The mating season lasts from September to January, and unlike most snakes, the Aruba Island rattlesnake is viviparous with females giving birth to live young rather than producing eggs (4). Females have small litters of five to nine young. The young are born weighing about 14 grams and are only a few inches long. They have fully functioning venom sacs or glands, and are independent from birth (2). Individuals live for between 15 and 20 years (4).

This species is threatened because it only occurs on one small island, where just ten square kilometres of habitat remains undisturbed. In past centuries much of the island’s trees were cut down for charcoal and firewood, removing this snake's shelter and prey (6). Recent threats include resort development on the island and other forms of human encroachment. Goats have been introduced and have wreaked havoc on the vegetation. This species is also caught and illegally exported for the pet trade (4).

The Government and people of Aruba do recognise this endemic species as important, and have set aside a large area of interior land as protected habitat for this and other species (2). The American Zoo and Aquarium Association (AZA) Aruba Island rattlesnake Species Survival Plan (SSP) is currently building on the island’s conservation efforts. Field research is being carried out to determine population size, natural history traits and factors affecting the survival of the Aruba Island rattlesnake in order to best inform conservation efforts. There is also an ongoing public relations campaign to change local people’s perceptions of this venomous snake (6). Captive breeding has also been initiated in zoos associated with the SSP program, to increase population numbers and the genetic health of this threatened snake (4) (6).

View information on this species at the UNEP World Conservation Monitoring Centre.

For further information on the conservation of reptiles see:

• International Reptile Conservation Foundation:
  http://www.ircf.org