It has a wide, triangular-shaped head, and eyes with vertical pupils. Like all pit vipers, it is solenoglyphous, having large, hypodermic needle-like fangs in the front of the upper jaw that fold back when not in use, and has heat sensitive organs, or pits, located on either side of the head between the eye and nostril.
Its most distinguishing feature, and origin of its common name, is the set of modified scales above the eyes that look much like eyelashes. The eyelashes are thought to aid in camouflage, breaking up the snake's outline among the foliage where it hides. The Eyelash Viper occurs in a wide range of colors, including red, yellow, brown, green, even pink, as well as various combinations thereof. It often has black or brown speckling on the base color. No external features distinguish the two sexes.
Like other viper members, the Eyelash Viper is arboreal and has a strong prehensile tail. It is largely nocturnal, consuming small rodents, frogs, lizards and small birds. It is not known to be an aggressive snake, but will not hesitate to strike if harassed.
A typical ambush predator, it waits patiently for unsuspecting prey to wander by. Sometimes, it is known to select a specific ambush site and return to it every year in time for the spring migration of birds. Studies have indicated that the Eyelash Viper learns to improve strike accuracy over time. Sometimes the Eyelash Viper(especially juveniles) will employ what is known as “ luring”, wiggling the tail in worm-like motions to encourage potential prey to move within striking range.
There is a myth among villagers in some small areas of South America that the Eyelash Viper will wink, flashing its "eyelashes" at its victim, following a venomous strike. Snakes are not physiologically capable of such behavior, as they have no eyelids and can not close their eyes.