New Yellow-Snouted Pit Viper Discovered in the Limestone Karsts of Laos

Deep in the limestone karst forests of Vang Vieng, in north-western Laos, a venomous snake has been hiding in plain sight. Researchers surveying caves and rock formations in Vientiane Province have described a previously unknown species of lance-headed pit viper, naming it Protobothrops flavirostris after the striking yellow-orange colouration of its snout. The discovery, published in the journal Herpetozoa, is based on a single adult female collected in October 2024 near the Khan Kham Cave, supported by photographic records of three other individuals from nearby caves. The find raises the number of Protobothrops species known from Laos to three and brings the global count of the genus to sixteen.

The genus Protobothrops, the Asian lance-headed pit vipers, comprises terrestrial, highly venomous snakes distributed across South, Southeast and East Asia. These snakes matter medically as well as scientifically: bites from Protobothrops species can be dangerous to humans, making accurate taxonomy a public health issue as much as an academic one. Yet the genus has long been taxonomically contentious, particularly the widely distributed species complexes such as P. jerdonii and P. mucrosquamatus. Recent molecular studies have repeatedly shown that the diversity of these pit vipers is underestimated, with new species described in rapid succession over the past decade, and the Lao snake now joins that growing roster.

During fieldwork in October 2024, conducted along the base of limestone karst formations and within caves in Vang Vieng District, the team encountered a single snake that its external morphology suggested belonged to Protobothrops. The specimen was collected with snake hooks, photographed alive, and later deposited in the collection of the National University of Laos in Vientiane. Tissue samples from the liver and heart were preserved in 96% ethanol before fixation, allowing the researchers to build a genetic profile of the animal that would prove decisive for the species description.

The molecular work was unusually thorough for a single-specimen study. The team sequenced a total of 6,092 aligned base pairs from five mitochondrial genes — complete sequences of cytochrome b, ND4 and COI, plus fragments of 12S and 16S rRNA — and two nuclear genes, c-mos and RAG1. Phylogenetic trees reconstructed with both Maximum Likelihood and Bayesian Inference methods confirmed that the animal belonged firmly within Protobothrops and, more tellingly, that it formed a deeply divergent lineage sister to P. kelomohy, a species described only in 2020 from the Dawna Range of north-western Thailand. The two Indochinese species form a strongly supported clade together with two Himalayan relatives, P. himalayanus and P. kaulbacki.

The genetic divergence between the Vang Vieng snake and its Thai sister species was substantial. In the cytochrome b gene, the uncorrected p-distance between the Lao specimen and P. kelomohy was 7.8%, a level comparable to or exceeding the distances separating many recognised species pairs in the genus, such as P. maolanensis and P. elegans at 7.9%. The new snake was most distantly related to the wide-ranging P. mucrosquamatus, at 15.7%. Crucially, analyses of the two nuclear genes revealed that the Lao population carried unique haplotypes not shared with any other Protobothrops species for which comparable sequences exist, indicating an independently evolving lineage rather than merely an isolated population of a known species.

Morphology backed up the genetics. The holotype, an adult female measuring 825 millimetres in total length, displays a distinctive combination of traits: dorsal scales arranged in 23–21–17 rows, all keeled; 215 ventral scales; 79 paired subcaudal scales; 7–8 supralabials; and no horn-like projections above the eyes. Its colouration is equally diagnostic — a blackish-brown head with yellow-orange markings on the rostral and adjacent scales, three faint dark vertical stripes on the snout, and a brown to greyish-brown body adorned with large dark reddish-brown, cross-shaped blotches edged in black that fuse into an interrupted zigzag line. Bright yellow colouration on the tip of the tail and the snout appears consistently across the photographic records and separates the species sharply from its Thai relative.

Compared one by one with all fifteen previously recognised congeners, the new species holds up. It differs from P. cornutus in ventral scale counts and the absence of supraocular horns, from the Japanese island endemics P. flavoviridis and P. tokarensis in having far fewer dorsal scale rows, and from P. mangshanensis in the number of labial scales, among many other characters. Even against P. kelomohy, its closest relative, the differences are consistent: fewer ventrals, fewer mid-body scale rows, fewer infralabials, two loreal scales instead of one, more dorsal blotches, and the signature yellow-orange snout and tail that P. kelomohy entirely lacks. Under the general lineage concept of species, the combination of molecular monophyly, unique nuclear haplotypes, diagnostic morphology and geographic isolation supports formal recognition as a new species.

The ecology of the snake is as intriguing as its taxonomy. All four known individuals were observed on limestone rocks, stalactites or cave walls, and the holotype proved an agile climber, anchoring itself with its prehensile tail. The species is nocturnal, with the type specimen collected at a quarter past nine in the evening, although cave encounters occurred during daytime. Records cluster at the beginning and end of the rainy season, a pattern echoed by local Hmong villagers, who know the snake as

Subject of Research: A new endemic karst-associated species of lance-headed pit viper (Squamata, Viperidae, Protobothrops) from Laos

Article Title: A new endemic karst-associated species of lance-headed pit viper ( Squamata , Viperidae , Protobothrops ) from Laos

Article References: Grassby-Lewis, R. J., Brakels, P., Maury, N., Sitthivong, S., Frohlich, D., Pawangkhanant, P., Idiiatullina, S. S., Nguyen, T. V., & Poyarkov, N. A. (2025). A new endemic karst-associated species of lance-headed pit viper (Squamata, Viperidae, Protobothrops) from Laos. Herpetozoa, 38, 43-60. https://doi.org/10.3897/herpetozoa.38.e146004

Image Credits: AI Generated

DOI: 10.3897/herpetozoa.38.e146004

Keywords: endemic, karst-associated, species, lance-headed, viper, Squamata, Viperidae, Protobothrops, Laos, scientific research