For nearly 180 years, the eyelash palm-pitviper has been one of the most recognizable snakes on Earth, a small, arboreal ambush predator whose enlarged scales above the eyes resemble a set of ornamental lashes. Its astonishing range of colors, from vivid green to golden yellow to pink-flecked gray, has made it a favorite of photographers and herpetologists alike. But that same dazzling variability has long frustrated scientists trying to determine whether they were looking at a single, wildly polymorphic species or a cluster of distinct evolutionary lineages hiding in plain sight. A new study, published in the journal Evolutionary Systematics, has finally delivered an answer, and it is a dramatic one: what has been called Bothriechis schlegelii is actually a complex of at least ten separate species.
The research team, led by Alejandro Arteaga and colleagues, undertook the most comprehensive taxonomic review of the eyelash viper ever attempted. The work rested on three pillars of evidence: the examination of 400 fluid-preserved museum specimens drawn from more than thirty herpetological collections across the Americas and Europe, a phylogeographic analysis of 818 locality records spanning the species’ entire range, and DNA sequence data from 80 individuals sampled for molecular characters. By integrating morphology, genetics, geography, and ecology, the authors applied what taxonomists call an integration-by-congruence approach, recognizing species only when three or more independent lines of evidence converge on the same conclusion.
The genetic analysis was itself a technical feat. The researchers generated 206 new DNA sequences and combined them with 73 downloaded from GenBank, producing a matrix of 279 sequences across seven gene fragments, including mitochondrial markers such as 12S, 16S, COI, CYTB, and ND4, and nuclear genes NT3 and RAG1. These fragments were aligned, partitioned by codon position, and analyzed under Bayesian inference in MrBayes, with each of four independent analyses running for 20 million generations. The resulting phylogeny confirmed something troubling that earlier studies had hinted at: Bothriechis schlegelii, as traditionally defined, was paraphyletic, meaning the species as circumscribed did not include all of its own closest relatives. In other words, the name was biologically meaningless as a label for a single evolutionary unit.
Perhaps the most remarkable methodological achievement was the successful sequencing of the two historic type specimens on which the entire species complex rests. The holotype of B. schlegelii, a juvenile collected in Popayán, Colombia, and described by Arnold Berthold in 1846, and the holotype of B. nigroadspersus, an adult female described by Franz Steindachner in 1870, were both analyzed using ancient DNA techniques. This allowed the team to anchor the oldest available names in the group to specific branches of the phylogenetic tree, a critical step in deciding which populations keep the original name and which must receive new ones.
The results revealed a deep continental split. Within the eyelash viper complex, two strongly supported reciprocally monophyletic clades emerged: one confined to Central America and the other to South America. The Central American clade contains the previously recognized Blotched Eyelash-Pitviper, Bothriechis supraciliaris, along with a second species for which the old name B. nigroadspersus was resurrected, now proposed as the Central American Eyelash-Pitviper. This species ranges from the Isthmus of Tehuantepec in Mexico to extreme northwestern Colombia, spans an estimated 352,139 square kilometers, and includes the famous golden oropel morph. It is also the most medically significant member of the group, responsible for nearly 19 percent of snakebites recorded in Costa Rica in 1979, with a hemotoxic, strongly myonecrotic venom and an estimated lethal dose as low as 1.7 milligrams per kilogram in mice.
The South American clade proved far richer in hidden diversity, harboring eight species-level lineages. Five of these are entirely new to science and are described in the paper: B. klebbai and B. khwargi from the slopes of Colombia’s Cordillera Oriental, B. rasikusumorum from the upper Río Magdalena watershed in Huila department, B. rahimi from the Chocó lowlands of northwestern Ecuador and adjacent Colombia, and B. hussaini from the transition zone between the humid Chocó rainforests and the dry Tumbesian forests of southwestern Ecuador and extreme northwestern Peru. Three additional names were revalidated from nineteenth-century obscurity: B. nitidus, described by Albert Günther in 1859 and now applied to a green, red-banded species endemic to west-central Ecuador; B. torvus, named by Andrés Posada Arango in 1889 and restricted to the Chocó and Río Magdalena valley regions; and B. nigroadspersus itself. The original B. schlegelii, now the Highland Eyelash-Pitviper, turns out to be a Colombian endemic confined to the Cordillera Occidental and Cordillera Central at elevations above roughly 1,000 meters.
Distinguishing these species required a meticulous dissection of anatomy that goes far beyond color. The researchers scored 21 morphological characters for each candidate lineage, weighting scale arrangement on the head, or lepidosis, most heavily, followed by the architecture of the hemipenes, the paired reproductive organs of male snakes whose spines, hooks, and calyces often differ sharply even between closely related species. They also compared coloration, body size, and even venom properties. The new species differ in subtle but consistent ways: B. klebbai has low, granular supraciliary scales and prominent black speckling on its dorsal and ventral surfaces, while B. khwargi, its sympatric neighbor on the Serranía de los Yariguíes, is smaller, has a pale white belly, keeled anterior head scales, and no black speckling at all. B. hussaini, meanwhile, can be separated from its sister species B. nitidus by the contact between the loreal and preocular scales, the density of black stippling on its green dorsum, and basal hooks on the hemipenial body that are roughly four times, rather than twice, the size of adjacent spines.
The species concept guiding these decisions follows de Queiroz’s general lineage concept: candidate species had to form a monophyletic group in mitochondrial DNA, diverge from other such groups by more than 4 percent sequence divergence in a 700-base-pair fragment of the CYTB gene, be diagnosable by external characters and hemipenial morphology, and show ecological and biogeographic congruence. Even so, the authors are candid about the remaining puzzles. B. nitidus and B. hussaini, for instance, are strongly supported as reciprocally monophyletic yet differ by only 1.5 percent in CYTB, less than the variation found within B. nigroadspersus. The team found the two species co-occurring along Andean foothills in Ecuador, exactly where their predicted distributions overlap, suggesting a scenario of secondary contact after isolation, though whether hybridization occurs in this zone remains an open question for future genomic work.
The taxonomic upheaval carries urgent conservation implications. Because the newly recognized species have far smaller ranges than the sprawling distribution once attributed to B. schlegelii, several now qualify for elevated threat categories under IUCN criteria. B. supraciliaris, with an extent of occurrence of roughly 3,568 square kilometers of severely fragmented cloud forest in Costa Rica and Panama, is considered Endangered, with an estimated 37 percent of its forest cover already destroyed. B. khwargi, B. rasikusumorum, B. rahimi, and B. hussaini are all assessed as Vulnerable, with between 49 and 79 percent of the forest cover across their potential distributions lost, mostly to the expansion of the agricultural frontier. Field biologists interviewing coffee plantation workers in Huila learned that the workers routinely kill these vipers on sight, and a ten-night expedition failed to find a single B. rasikusumorum at four localities where the species had recently been recorded. Only the widespread Central American B. nigroadspersus, which tolerates moderate habitat degradation and occurs in dozens of protected areas, is considered of Least Concern.
The study also resolves a long-standing biogeographic curiosity. B. hussaini’s distribution mirrors that of several other recently described reptiles restricted to the same Chocó-Tumbes transition zone, including specific species of Enyalioides, Anadia, Dipsas, Sibon, and Anolis, each with a sister species endemic to west-central Ecuador. The authors argue that this repeated pattern points to the existence of a unique, previously underappreciated biogeographic province between the humid Chocó rainforests and the Tumbesian dry forests. Much work remains: relationships among the Colombian species are still weakly supported, the hemipenes of adult male B. khwargi and of B. rahimi remain unknown, and the status of populations separated by the Río Atrato valley awaits genetic sampling. But after nearly two centuries of confusion, the eyelash vipers finally have a stable taxonomic foundation, one that transforms a single famous snake into a radiation of ten, each now visible, nameable, and, crucially, capable of being protected in its own right.
Subject of Research: Systematic revision and species delimitation of the Eyelash Palm-Pitviper (Bothriechis schlegelii) species complex
Article Title: Systematic revision of the Eyelash Palm-Pitviper Bothriechis schlegelii ( Serpentes , Viperidae ), with the description of five new species and revalidation of three
Article References: Arteaga, A., Pyron, R. A., Batista, A., Vieira, J., Meneses Pelayo, E., Smith, E. N., Barrio Amorós, C. L., Koch, C., Agne, S., Valencia, J. H., Bustamante, L., & Harris, K. J. (2024). Systematic revision of the Eyelash Palm-Pitviper Bothriechis schlegelii (Serpentes, Viperidae), with the description of five new species and revalidation of three. Evolutionary Systematics, 8(1), 15-64. https://doi.org/10.3897/evolsyst.8.114527
Image Credits: AI Generated
DOI: 10.3897/evolsyst.8.114527
Keywords: Bothriechis schlegelii, eyelash viper, taxonomy, phylogenetics, new species, pitvipers, Colombia, Ecuador, Central America, venom, conservation, herpetology
News Source: Margaret Porter. (October 18, 2026). One Famous Snake Becomes Ten: Eyelash Viper Split Reveals Hidden Species Across Latin America. Scienmag.
