High in the Venezuelan Andes, in the shallow margins of ponds sitting more than 3,500 meters above sea level, scientists have identified two diving beetle species previously unknown to science. The beetles, both belonging to the genus Liodessus, were described from specimens collected around Mérida in the Venezuelan Andes, including Laguna de Mucubají and sites near Pico Bolívar and the village of Gavidia. One species has been named Liodessus meridensis, after the state of Mérida where the collecting localities are situated, and the other Liodessus venezuelanus, after the country of origin.
The discovery matters because it extends a rapidly growing catalog of high-Andean water beetles. Liodessus beetles are small, usually less than 3 millimeters long, and occur in the New World as well as the Afrotropical region. In the high Andes, at altitudes from roughly 3,000 to nearly 5,000 meters, they are probably the most abundant aquatic beetles. Yet diving beetles from such high altitudes of the Páramo and Puna regions remain poorly studied. Since 2019, eleven new species have been described from Peru and Colombia, and it has become apparent that many more remain to be discovered, most of them likely microendemics, species restricted to very small geographic areas. The two Venezuelan species are the first high-altitude Liodessus reported from that country, and the authors expect additional species to surface in the vast, unsampled Venezuelan mountain regions.
The formal description rests on a combination of morphological characters and DNA sequence data. The researchers delineated the species using features such as male genital structure and beetle size, shape and color. Mitochondrial cox1 sequence data provided an additional character source. The team delivered tissue samples to the Canadian Centre for DNA Barcoding, where they were processed under standard barcoding procedures and the resulting barcode data uploaded to the Barcode of Life Data System, known as BOLD. From there, the researchers calculated a neighbour-joining tree using p-distances in Geneious software to learn whether newly added entries could be assigned to existing species groups.
That DNA-based approach proved useful in a practical sense. According to the authors, it has been helpful in guiding the morphological descriptive process, not least by enabling them to unambiguously identify the new species, even in the absence of male specimens. In the BOLD project maintained for these beetles, Liodessus meridensis is well delineated from all other Liodessus, with an uncorrected p-distance of around 9 percent or more, while Liodessus venezuelanus is similarly well delineated with an uncorrected p-distance of around 8 percent or more. Both species were represented by a single entry each in the project.
The morphological evidence is detailed and, in places, subtle. Liodessus meridensis has a total length of 2.1 millimeters in the holotype, with a length without head of 1.9 millimeters and a maximum width of 0.9 millimeters; paratypes range from 2.1 to 2.3 millimeters in total length. Its habitus shows only slight discontinuity between pronotum and elytron, the pronotum is widest before its base and more parallel sided laterally, and the beetle is very dark brown to blackish dorsally and ventrally, with the basal antennomeres and the base of the meso- and metatibia contrastingly lighter. The head lacks an occipital line, the pronotum carries distinct lateral beads and long, deep basal striae, and the elytron bears a short basal stria without a sutural line or basal epipleural transverse carina. The median lobe of the aedeagus shows a long, simple curvature in lateral view, gradually narrowing towards a narrow tip in both lateral and ventral views, with parameres of the simple two-segmented Bidessini type.
Liodessus venezuelanus is similar in overall appearance but distinguishable on close inspection. Its holotype measures 2.2 millimeters in total length, 2.0 millimeters without the head, and 1.0 millimeter at maximum width, with paratypes spanning 2.0 to 2.3 millimeters. The habitus shows a more evident discontinuity between pronotum and elytron, and the pronotum is more rounded laterally. The head carries an occipital line, a feature absent in its congener, and the median lobe of the aedeagus is broadened towards the apex and then narrows in lateral view, broadening towards a broadly rounded tip in ventral view.
The holotype of Liodessus meridensis is a male collected at Laguna de Mucabají, Mérida, at 3,500 meters in January 2004, with thirteen paratypes from the same locality and forty-seven more from a lagoon margin about 5 kilometers east of Gavidia at 3,600 meters, collected in January 2012. The holotype of Liodessus venezuelanus comes from the same 2004 Laguna de Mucubají sample, with additional paratypes from Pico Bolívar’s Laguna de Gallo at 4,000 meters, collected in December 1998, and from the Gavidia site. Specimens are housed at the Museo del Instituto de Zoología Agrícola in Venezuela, the Zoologische Staatssammlung in Munich, the Natural History Museum and Biodiversity Research Center at the University of Kansas, and the private collection of D. T. Bilton in Plymouth.
Both species were collected in shallow water at the edge of high-altitude ponds, a habitat captured in photographs from near Gavidia where both new species were found together. Females show variation worth noting: in Liodessus meridensis, the pronotum and elytra are microreticulate and dull in specimens from Gavidia but shiny in those from Laguna de Mucabají, while in Liodessus venezuelanus the pronotum and elytra are microreticulate and dull in specimens from Laguna de Gallo but shiny in the single females from Laguna Mucabají and Gavidia. In a few paratypes of each species, the elytral striae are hardly noticeable, underscoring how much of the species discrimination rests on genital structure and molecular data rather than external appearance alone.
The paper also presents an updated checklist of the high Andean species of Liodessus, which now runs to sixteen species-level entries, from Liodessus acollensis in Peru and Liodessus andinus in Bolivia to the two new Venezuelan additions at the end of the list. The checklist documents how knowledge of this radiation has accumulated, with recent descriptions from Peru and Colombia joining older names dating back to the 1950s. Against that backdrop, the Venezuelan pair fills a conspicuous geographic gap in a genus whose high-Andean members were, until now, formally known only from countries further along the cordillera.
The authors are careful about what the genetic evidence can and cannot show. They note that one genetic marker alone cannot be the ultimate tool for taxonomy, particularly markers such as cox1, which are not involved in speciation per se. Rather, such DNA sequence data can be used to guide the sorting of specimens into operational units and support the taxonomic decision-making process, an approach they say has been used successfully to study very diverse beetle taxa, including their own previous work on Liodessus. The method can be technically scaled up massively using next-generation sequencing technology, which also reduces analytical costs. Such data do not, however, replace taxonomic expertise and the evaluation of morphological structure. The phylogenetic position of the two new species remains to be established based on a multigene dataset, leaving one more question open for future work on these minute beetles of the páramo ponds.
Subject of Research: Taxonomic description of two new high-Andean Liodessus diving beetle species from Venezuela using morphology and mitochondrial cox1 DNA barcoding
Article Title: Two new high Andean species of Liodessus diving beetles from Venezuela ( Coleoptera , Dytiscidae , Bidessini )
Article References: Balke, M., Bilton, D. T., García, M., Viloria, Á. L., Villastrigo, A., & Hendrich, L. (2022). Two new high Andean species of Liodessus diving beetles from Venezuela (Coleoptera, Dytiscidae, Bidessini). Alpine Entomology, 6, 7-12. https://doi.org/10.3897/alpento.6.79598
Image Credits: AI Generated
Keywords: Liodessus, diving beetles, Dytiscidae, Venezuela, Andes, new species, taxonomy, DNA barcoding, BOLD, Páramo, high altitude, Mérida
News Source: Gavin Prescott. (October 27, 2026). Two Tiny New Diving Beetle Species Discovered in Venezuela’s High Andes. Scienmag.
