Eyelash Viper

About the eyelash viper

The eyelash viper is a small pit viper in the family Viperidae, and its most obvious feature is right there in the name: a set of modified scales above each eye that look like a fringe of eyelashes. Those scales are thought to help the snake blend into foliage by breaking up the outline of its head. The species also carries distinctly keeled, or raised, scales across most of its body, giving it a slightly rough texture rather than the smooth sheen of many other snakes.

Adults run 55 to 82 cm (22 to 32 in) in length, with females growing longer and more variable in size than males, which top out around 69 cm (27 in). The head is broad and triangular, the eyes have vertical pupils, and like all pit vipers it has heat-sensing pits between the eye and nostril on each side of its head, along with long, hinged fangs at the front of the upper jaw that fold back when not in use. One of the eyelash viper's best-known traits is color: individuals appear in a wide range of morphs, from mottled browns and greens to bright yellow forms sometimes called "oropel." No external markings separate males from females.

The species was long thought to range from southern Mexico down through Central America into northwestern South America, and it carries a long list of common names in both English and Spanish reflecting that broad reputation, including bocaracá, oropel, and víbora de pestañas. A 2024 genetic study revised that picture substantially: researchers split what had been treated as one wide-ranging species into several separate species, several with their own names. What is now recognized as Bothriechis schlegelii in the strict sense is restricted to Colombia, mostly in highland regions, with its closest relatives forming what researchers call the "eyelash clade" within the genus Bothriechis.

Behavior and diet

The eyelash viper is almost entirely arboreal, using a strong, prehensile tail to anchor itself around tree limbs. By day it is typically coiled into a tight bundle, since the species is primarily nocturnal and becomes active after dark. It hunts as a sit-and-wait ambush predator, holding a position and striking at small animals that pass within range rather than pursuing prey across distance. Recorded prey includes tree-dwelling mammals such as rodents, bats, and mouse opossums; amphibians including cloud forest and fleshbelly frogs and tree frogs; birds such as hummingbirds; lizards including anoles, geckos, juvenile iguanas, and whiptails; and occasionally fish.

Some individuals return to the same ambush perch year after year, timed to coincide with spring bird migration, and studies have found that individual snakes appear to sharpen their strike accuracy with practice over time. Juveniles in particular sometimes use a technique called caudal luring, wriggling the tip of the tail in a worm-like motion to draw hungry frogs or lizards within striking distance.

The eyelash viper reaches sexual maturity at around two years old. It is ovoviviparous, meaning females carry developing eggs internally for about six months before giving birth to live young rather than laying eggs. A typical litter runs from 2 to 20 offspring, each 15 to 20 cm (6 to 8 in) long and already resembling miniature adults. Late-stage pregnant females often stop eating and show a visibly enlarged lower abdomen. Males compete for mates in a ritual sometimes called the "dance of the adders," in which two rival males rear up in a cobra-like posture and push against each other until one is toppled or backs away; the species is polygynous and mating typically happens at night.

Range and habitat

Following the 2024 taxonomic revision, the range of Bothriechis schlegelii in the strict sense is restricted to Colombia, where it is found primarily in highland regions. Earlier accounts describing a much wider range from southern Mexico to northwestern South America now refer, in part, to the newly separated species that were split out of the old, broadly defined population.

Within its range, the eyelash viper is not confined to pristine wilderness. The species has proven adaptable enough to persist in secondary forest — regrowth following earlier clearing — as well as in agricultural land such as coffee and banana plantations, provided there is enough tree cover and vegetation for an arboreal ambush hunter to work with.

Conservation status

The eyelash viper was evaluated for the IUCN Red List and classified as Least Concern in 2013, and it was removed from CITES Appendix III in 2002, meaning it is not currently subject to that international trade-monitoring listing. It is not considered threatened with extinction.

That status comes with a caveat rather than a clean bill of health: the species does face pressure from habitat loss as forest is cleared for timber, agriculture, and urban development. Its tolerance for secondary forest and certain plantation crops appears to be helping it withstand some of that pressure better than a habitat specialist might.