Mexican horned pitviper  (Ophryacus undulatus)

The Mexican horned pitviper is classified as Vulnerable (VU) on the IUCN Red List (1).

The Mexican horned pitviper (Ophryacus undulatus) is a rare, venomous snake about which very little is known. It can be easily distinguished from most other vipers by the raised scales above its eyes, giving the appearance of horns (3).

The Mexican horned pitviper varies in colour throughout its range, from grey to green on the upperparts (3), typically with yellowish underparts (2). There is an irregular, darker zigzag pattern along its back (2) (3).

Like other vipers (species in the Viperidae family), the Mexican horned pitviper has a triangular-shaped head, vertical pupils, and long, pointed, curved fangs. The fangs are hinged, allowing them to lie flat against the roof of the mouth when the mouth is closed, and then rotate forward when the viper is ready to strike. Venom, produced in glands at the back of the head, flows through the fangs into the prey (4).

Pitvipers are named after the pair of small pits situated between the eye and nostril. These pits are sensitive to heat, helping the Mexican horned pitviper to locate warm-blooded prey (4).

As its name suggests, the Mexican horned pitviper is found only in Mexico, where it is present in isolated populations in the southern parts of the Sierra Madre Oriental and the Sierra Madre del Sur mountain ranges. It has been reported in the states of Hidalgo, Veracruz, Puebla, Oaxaca and Guerrero (1).

The Mexican horned pitviper generally occurs in pine-oak forest and cloud forest, at elevations between 1,800 and 2,800 metres. It has also been recorded in corn fields (1).

The Mexican horned pitviper hunts rodents (3), using the heat-sensitive organs on its head to locate these warm-blooded mammals (4). It also takes small lizards (3). When ready to strike, the Mexican horned pitviper erects its fangs and thrusts them into the prey (4). The venom that flows through the fangs into the prey affects the blood, causing the prey to die quickly of internal bleeding and haemorrhaging (5).

Unlike many other reptiles, which lay eggs, the Mexican horned pitviper bears live young. The female Mexican horned pitviper typically gives birth to between 6 and 13 young at a time (3).

The primary threat to the Mexican horned pitviper is the loss of its habitat to agriculture and logging (1) (6). Pine-oak forest once covered around 21 percent of Mexico, but now covers no more than 8 percent (6), and the remaining habitat of the Mexican horned pitviper is severely fragmented (1).

Like many snakes, the Mexican horned pitviper suffers from persecution, and is often killed by locals if encountered (1).

Although there are no specific conservation efforts in place for the Mexican horned pitviper, it is present in at least three protected areas (1), and several conservation organisations are working to preserve Mexico’s pine-oak forests (6). For example, Pronatura Noreste works in the Sierra Madre Occidental and Sierra Madre Oriental to conserve and promote the sustainable use of natural resources (6) (7). Such efforts will likely benefit this highly threatened snake.

Learn more about conservation in Mexico:

• The Nature Conservancy:
  http://www.nature.org/ourinitiatives/regions/northamerica/mexico
• Pronatura Noreste:
  https://www.pronaturane.org/
• Fondo Mexicano para la Conservación de la Naturaleza:
  http://www.fmcn.org/