Mexican cantil  (Agkistrodon bilineatus)

Classified as Near Threatened (NT) on the IUCN Red List (1).

The Mexican cantil is a venomous pitviper that is greatly feared by humans throughout its range (2). Like all pitvipers, the Mexican cantil has a pair of heat-sensitive pits, located between the eye and nostril on each side of the head (2). Its body is a dark brown ground colour, overlaid with darker brown or black bands, often fringed with white or cream scales (2). Juvenile cantils usually possess more distinctive banding and brightly coloured tails, used to lure prey (2) (4).

The generic name, Agkistrodon, is derived from the Greek Ancistro,meaning ‘hook’, and odon, meaning ‘tooth’, referring to the hinged, hollow fangs of this species (2). The Mexican cantil has the longest fangs of any species within the Agkistrodon genus, growing to over one centimetre in length (2). The specific name, bilineatus, refers to the pair of striking pale stripes on each side of the head: bi-means 'two' and lineatus means 'lined' in Latin (2).

The Mexican cantil is comprised of three geographically distinct subspecies (2) (3). The subspecies Agkistrodon bilineatus bilineatus occurs along the Pacific coast of Central America, from southern Sonora, Mexico, through Guatemala to El Salvador (5). Agkistrodon bilineatus howardgloydi is distributed throughout north-western Costa Rica and western Nicaragua, and has a limited range in El Salvador and Honduras (5). Agkistrodon bilineatus russeolusis found in northern Belize and the Yucatán Peninsula, Mexico (5).

The Mexican cantil occurs in a vast range of habitats, including seasonally dry forest, tropical deciduous forest, tropical scrub forest and savanna (2). Habitat bordering rivers or streams is preferred, but it may also occur in grasslands and cultivated lands (1).

The diverse habitats occupied by the Mexican cantil throughout its range suggest it is a semi-aquatic species (2). Individuals have been recorded swimming in streams, marshes and even roadside ditches after nightfall, and the majority of evidence indicates that this species is primarily active at night (2). Adult cantils prey upon a variety of vertebrates, including amphibians, reptiles, birds and mammals (2), and there is a single record of a treesnake being consumed (6). Juveniles lure potential prey by ‘wiggling’ the bright yellow tail as if to mimic an invertebrate, attracting frogs and lizards (2) (7).

The Mexican cantil gives birth to live young (2). Mating usually occurs between December and April, with individuals giving birth from June until August, during the rainy season (2). There are usually five to ten young in a litter, although extremes of three to twenty have been recorded (2).

Despite its extensive distribution throughout Central America, the Mexican cantil is one of the most endangered snakes in the Americas (2). This is due to the conversion of tropical forest and thorn scrub for agricultural purposes (5), combined with human persecution throughout its fragmented range (1). Populations have suffered declines of nearly 30 percent over the past 30 years and, sadly, populations continue to decrease today (1).

The Mexican cantil occurs in two protected areas in Mexico: the Calakmul Biosphere Reserve and the Chamela Biological Station (1). The species is not currently afforded any protection from international trade by the Convention on International Trade in Endangered Species (CITES) (8).

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

To learn about efforts to conserve snakes around the world see:

• International Reptile Conservation Foundation:
  http://www.ircf.org
• Amphibian and Reptile Conservation:
  http://www.arc-trust.org