The order Dermaptera, to which earwigs belong, is divided into major lineages defined largely by the anatomy of the male genitalia, in particular the number and orientation of the penis lobes. Within one of these lineages sits the family Anisolabididae, a sprawling group containing eleven subfamilies. Its largest subfamily, Anisolabidinae, holds roughly 300 species, yet its internal classification has long been a source of frustration. Genera within it have traditionally been defined on the basis of a single male genital structure, the parameres, a practice that has produced severe confusion and inconsistency among researchers. Compounding the problem, previous molecular surveys sampled only a limited slice of the group’s diversity, leaving relationships among subfamilies unresolved and offering no consensus on shared derived characters that could define each branch.

The new work began during field surveys in Indonesia and neighboring Southeast Asian countries, when the first author collected specimens of Epilandex from Taiwan, Laos, and Indonesian Borneo. The genus comprises 14 named species of small earwigs known from both the Old and New Worlds, and it has traditionally been placed within Anisolabidinae. To test that placement, the team analyzed 24 adult specimens of anisolabidid species and generated the first molecular data ever obtained for Epilandex, sequencing partial fragments of three genetic markers: the mitochondrial cytochrome c oxidase subunit I gene, the standard 663-base-pair DNA barcode region, together with two nuclear ribosomal genes, 18S and 28S rDNA. Two species of Labiduridae, a family regarded as the sister group to Anisolabididae in many earlier studies, served as outgroups.

The laboratory workflow followed established protocols. A single leg was removed from each ethanol-preserved specimen and digested in a Chelex-proteinase K solution incubated overnight at 56 degrees Celsius, then heated to 99 degrees to deactivate the enzyme. Polymerase chain reactions amplified each marker under gene-specific cycling conditions, and the products were verified on agarose gels, purified, and sequenced commercially. The resulting sequences were aligned with MUSCLE, concatenated by gene and codon position, and analyzed under both maximum likelihood and Bayesian inference frameworks. Substitution models for each partition were selected automatically under the Bayesian Information Criterion, and node support was assessed with ultrafast bootstrap replicates and Markov chain Monte Carlo sampling run for ten million generations, with convergence diagnostics confirming that the independent chains had mixed well.

The phylogenetic results were unambiguous. Representatives of four classic anisolabidine genera, Anisolabis, Anisolabella, Euborellia, and Gonolabis, clustered together in a single clade, but the Epilandex specimens fell clearly outside it. This separation was strongly supported by high bootstrap values and posterior probabilities, and it positioned the subfamily Brachylabidinae as the sister group to Anisolabidinae once Epilandex was excluded. In other words, the molecular tree showed that Epilandex is not just another anisolabidine genus but a distinct evolutionary lineage meriting recognition at the subfamily rank, a conclusion reinforced by independent morphological evidence.

That morphological evidence centers on a plate of the thorax called the metasternum. In every Epilandex specimen examined, the metasternum narrows toward the rear with a conspicuous constriction at the base of the hind legs, a feature found consistently in both sexes. In all other anisolabidines and in the brachylabidines examined, the metasternum narrows posteriorly without any such constriction. A review of earlier literature confirmed the same dichotomy. Combined with the genus’s signature male genitalia, in which the paired parameres are extraordinarily long and narrow, at least six times and usually more than ten times as long as their basal width, the metasternal constriction provides a robust diagnostic package for the new subfamily.

Naming that subfamily, however, required untangling a century-old nomenclatural mess. The genus Landex was established in 1915 for a single species, Labidura femoralis, along with a subfamily Landicinae. But the material underlying that original description actually contained two clearly distinct species, and the type species was later misidentified. Most contemporary researchers now place Labidura femoralis in the genus Euborellia because of its square-shaped parameres, which means the name Landicinae is anchored to the wrong genus and is therefore a synonym of Anisolabidinae. To resolve the inconsistency, the authors propose Epilandicinae as a new substitute name, defined by the morphological concept originally intended for Landicinae, and provide a revised identification key to the subfamilies of Anisolabididae.

The study also reshuffled species boundaries within the genus. The researchers examined high-resolution photographs of type specimens held in Taiwan and Copenhagen, including the holotype of Psalis kawakamii, a species described from Taiwan in 1928 and long shuffled into the genus Carcinophora. The holotype’s external morphology, notably the tips of long parameres protruding beyond a medially emarginate penultimate sternite, matched Epilandex perfectly. Meanwhile, DNA barcoding showed that specimens from Taiwan and Laos form one clade with internal divergence of at most 1.56 percent, below the 2 percent threshold often used as a rough yardstick for species boundaries, while Bornean specimens belong to a separate clade differing by more than 9 percent. The Bornean insects correspond to Epilandex peterseni, known from the Philippines and nearby islands, and the Taiwan-Laos insects correspond to kawakamii. As a consequence, the authors transfer kawakamii into Epilandex and synonymize the later name Epilandex acuminata, described from Hong Kong in 2003, under it.

Among the anatomical novelties reported is the first description of the female genitalia of Epilandex, specifically the spermatheca, the sperm-storage organ of the female reproductive tract. In both species it takes the form of a very long, thin, blind duct lacking a capsule at its distal end, a simple tubular configuration already known from many other anisolabidid species. The researchers also documented new distribution records, extending Epilandex kawakamii to Laos for the first time and Epilandex peterseni to Indonesian Borneo, and they noted that hindwing development and abdominal carination vary too much within species to serve as reliable diagnostic characters, a caution that explains some of the historical confusion in this group.

Perhaps the most intriguing suggestion concerns ecology. The Bornean specimens were collected in a conservation forest within oil palm plantations, while the Taiwanese and Laotian insects came from light traps, and most Epilandex specimens recorded in earlier studies were likewise captured with light, Malaise, or flight-intercept traps. This pattern suggests that members of the genus are predominantly arboreal and fly frequently, unlike their predominantly terrestrial relatives in Anisolabidinae. The authors hypothesize that the posterior narrowing of the metasternum may facilitate greater mobility of the hind legs, potentially enhancing locomotion on vertical substrates such as tree trunks. If confirmed, a tiny thoracic constriction, first noticed under a stereomicroscope, would link anatomy, genetics, and lifestyle in a single evolutionary story, and would remind taxonomists that even a group as familiar as earwigs still holds surprises at every level, from species to subfamily.

Subject of Research: Phylogenetics and taxonomy of the earwig genus Epilandex within the family Anisolabididae

Article Title: Revised placement of Epilandex Hebard, 1927 in Anisolabididae ( Insecta , Dermaptera ) with a re-evaluation of Carcinophora kawakamii (Shiraki, 1928) and Epilandex acuminata Srivastava, 2003

Article References: Revised placement of Epilandex Hebard, 1927 in Anisolabididae ( Insecta , Dermaptera ) with a re-evaluation of Carcinophora kawakamii (Shiraki, 1928) and Epilandex acuminata Srivastava, 2003. (n.d.). https://doi.org/10.3897/zookeys.1294.201081

Image Credits: AI Generated

DOI: 10.3897/zookeys.1294.201081

Keywords: earwigs, Dermaptera, Anisolabididae, Epilandex, taxonomy, molecular phylogeny, DNA barcoding, new subfamily, Epilandicinae, Southeast Asia, male genitalia, spermatheca