Eyelash Viper: where and when to see them

Bothriechis schlegelii is a venomous arboreal pit viper within the eyelash-viper complex, named for raised scales above the eyes. Its taxonomy is important here: recent revisions divide the former widespread species into several geographically restricted species, and Costa Rican populations are assigned other names under that treatment. Consequently, older Costa Rican records labelled schlegelii do not securely establish the narrowly defined species there. Measurements and conservation summaries from the former broad concept should not be transferred uncritically.

Size

Not reliably established

Weight

Not reliably established

Lifespan

Not reliably established

Status

Check current assessment

Eyelash vipers are ambush predators that may remain coiled on a branch or leaf for long periods, relying on concealment rather than continuous pursuit. Heat-sensitive facial pits assist in detecting warm-blooded prey. A prehensile tail anchors the body among vegetation, and activity is often nocturnal. Females bear live young. These general traits characterize the complex, but detailed ecological findings from Costa Rica cannot automatically be assigned to narrowly defined Bothriechis schlegelii. Beyond ambush predation, these vipers are known to exhibit caudal luring, wiggling their brightly colored tail tip to attract small prey. Their prehensile tail allows them to anchor firmly, often coiling around branches or vines in an 'S' shape, ready to strike. While generally nocturnal, they may also be observed basking during the day.

• The eyelash structures are modified scales, not hairs.
• Facial pits detect infrared radiation associated with warm objects.
• A prehensile tail helps secure the snake among branches.
• Recent taxonomic splits make many older photographs and records require reidentification.

There is no defensible Costa Rican observation season for narrowly defined Bothriechis schlegelii. Locally occurring relatives may be active throughout the year in humid forest, but rainfall-related activity does not resolve their identity. Confirm the taxonomic treatment before attaching any seasonal wildlife claims. For the *Bothriechis schlegelii* complex in Costa Rica, observations are possible year-round, especially in areas with consistent rainfall and high humidity. While some sources suggest increased activity during the wet season due to more abundant prey, this is not specific to the narrowly defined species.

Under recent restricted treatments, this species is associated with humid forest in northwestern South America, particularly Colombia, rather than Costa Rica. Vegetation above the ground provides hunting positions. Older descriptions spanning Central America combine populations now assigned to multiple species by some authorities. The species as currently understood prefers primary or mature secondary humid forest, often in lower montane or premontane zones. It is typically found at elevations ranging from sea level up to 1,500 meters, utilizing both arboreal and terrestrial microhabitats.

Reported prey within the eyelash-viper complex includes frogs, lizards, small mammals and birds, with prey choice influenced by snake size and local availability. Exact dietary proportions for narrowly defined Bothriechis schlegelii remain insufficiently documented, so Costa Rican feeding records require taxonomic checking. In the broader 'eyelash viper complex,' prey is usually swallowed headfirst, with the flexible jaws accommodating surprisingly large meals. While specific data for *Bothriechis schlegelii sensu stricto* is scarce, close relatives in Central America exhibit a diet heavily skewed towards frogs and lizards in juvenile stages, shifting to birds and small mammals as adults.

Common name

Eyelash Viper

Scientific name

Bothriechis schlegelii

Animal group

Reptiles

Size

Not reliably established

Weight

Not reliably established

Lifespan

Not reliably established

Status

Check current assessment

Identification

Raised eyelash-like scales identify the complex, but colour alone cannot distinguish schlegelii from recently separated relatives, and locality plus expert assessment are essential. Key identification features for *Bothriechis schlegelii* (s.s.) include a relatively small head with prominent supraocular scales forming the 'eyelashes' and a robust body. Coloration is highly variable, ranging from bright yellow to green, pink, or brown, and can include mottled or banded patterns.