The synonymization rests on close examination of the type material of S. razalii and comparison with specimens of F. dubius in Malaysian collections and photographs of the latter species’ type material available through the Orthoptera Species File. The authors detected no morphological differences supporting treatment of the two names as separate species. Falconius can be distinguished from other scelimenine genera by a swollen hind tarsus in females, a relatively stout head, a frontal costa that forks relatively close to the fastigium, anterior eye margins raised slightly above the fastigium, and relatively high positions of the paired ocelli and antennal grooves in relation to the compound eyes. The study also corrected an incorrect type-material listing in an earlier thesis and presented the museum records as the first official record of F. dubius from Peninsular Malaysia. Material reported as S. razalii from Pakistan was not examined, so its identity remains uncertain and requires re-examination.

The reappraisal also corrected numerous earlier identifications of S. gombakensis. Some Malaysian specimens had been labeled Scelimena producta, a species described from Java whose body coloration can resemble that of S. gombakensis. The two can be distinguished by features of the pronotum and hind femora: S. producta has pointed tubercles at the pronotal humeral angles and numerous clearly visible teeth on the ventral side of the hind femora, whereas S. gombakensis has rounded humeral angles and only two small teeth. Re-examination of museum holdings showed that the species had been present in collections for decades without being recognized as distinct from S. producta. This correction produced locality records in Selangor, Penang, Pahang, Perak, Kelantan, Negeri Sembilan, Johor and Terengganu, supplementing the physical and verified iNaturalist records assembled by the study.

The revision shows that S. gombakensis is not as restricted as an earlier account suggested. When it was described in 2018, the species was known from Sungai Gombak in the Gombak Catchment of Selangor. Museum material and verified citizen-science observations now place it across much of Peninsular Malaysia, especially along the west coast. The study included iNaturalist records available before its submission on 29 August 2022, with observers’ identifications checked by the authors. One record from Waeng district in Narathiwat, southern Thailand, close to the Malaysian border, is reported as the first official record outside Peninsular Malaysia and the first for Thailand. The authors did not directly compare S. gombakensis with Scelimena discalis specimens from Thailand because the physical specimens were inaccessible and molecular and suitable online data were lacking. They note that some Thai material identified as S. discalis may warrant renewed comparison.

Field observations at the Ulu Gombak Field Study Center indicate that S. gombakensis occupies a cool, humid and shaded habitat in lowland secondary rainforest. Individuals perch on river rocks near flowing water and tend to gather close to the surface, where the stream environment is humid. Lichen and moss are reported as the species’ food source. Juveniles were more often observed near the water than adults. The authors associate this pattern with two characteristics of immature individuals: their exoskeletons may make them more susceptible to desiccation, and they are less agile and unable to fly. Remaining near the water may therefore increase a juvenile’s chance of escaping a predator by diving. Adults and juveniles can occupy the same rock, but the egg-laying site of S. gombakensis remains unknown. Sand along riverbanks has been suggested as a possible egg-laying location for other Scelimena species.

Scanning electron micrographs revealed microscopic features on the hind tibia and first tarsal segment of S. gombakensis. The first tarsal segment is laterally compressed along its entire length, while both the tarsal segment and tibia carry serrations along their lateral edges. The authors suggest that compression may provide a wider surface for paddling and aid propulsion during swimming. Because the claws lack an arolium, the adhesive pad normally associated with them, the tarsal serrations may help the insect grip wet, slippery and porous rock surfaces. The serrations could also have a hydrodynamic function by reducing drag as the legs move underwater, limiting vortex formation and potentially making swimming more energy-efficient. Their orientation parallel to the direction of water movement is consistent with that possibility. These remain functional hypotheses based on morphology, not results from direct measurements of swimming performance, grip strength or energy use.

Behavioral observations suggest that S. gombakensis uses both its hind legs and hindwings for navigation and escape. The species was observed flying long distances and maneuvering effectively in flight, contrasting with the related S. songkrana from Thailand, which seldom flies and relies more often on jumping. Scelimena melli from China has been described as behaving similarly to S. gombakensis, although it can leap at least 10 metres. Mating behavior in S. gombakensis was consistent with observations of other Scelimena species, with the male positioning himself on top of the female. The authors also propose that S. gombakensis may disperse passively with water after diving, potentially connecting its distribution to large flowing bodies of water. That transport mechanism was inferred from the ecology and behavior rather than demonstrated directly.

Examination of the large museum series also revealed substantial variation in S. gombakensis. Adult males measured 18.0–24.0 millimetres, while females measured 24.0–31.0 millimetres. Nymphs broadly resemble adults in coloration and general appearance, although their shorter pronotum makes them readily distinguishable from other Tetrigidae in Peninsular Malaysia. One living individual had a brown body with orange markings rather than the more typical dark green coloration with yellow markings. The authors could not determine whether this unusual appearance was recessive or caused by an infection. Pinned specimens also faded from dark green with yellow markings toward brown, and older examples were generally more degraded than recent ones. Uneven fading among specimens collected around the same time and stored under similar conditions suggests that conditions before pinning, including collection, euthanization, pinning and preservation practices, may affect color retention, but information about those historical conditions was unavailable.

Malaysian Tetrigidae remain incompletely studied, with earlier publications concentrating largely on taxonomy, species descriptions and occurrence records. The present study combined revision of historical museum material, author-verified citizen-science observations, daytime field observations of behavior and food preference, and scanning electron microscopy of preserved legs. These approaches changed both the taxonomic arrangement and the known distribution of the genus. Type examination showed that S. razalii should be merged with F. dubius, while re-identification of older specimens and compilation of observation records showed that S. gombakensis extends well beyond its original Selangor locality and has been recorded in southern Thailand. The study also documented its association with humid river-rock habitat and described leg features consistent with possible swimming and gripping functions. Its conclusions remain bounded by the material available: the Pakistani S. razalii specimens were not reassessed, Thai S. discalis material could not be compared directly, and the proposed functions of the leg structures and water-mediated dispersal were not tested experimentally.

Subject of Research: Taxonomy, distribution, ecology and hind-leg morphology of Peninsular Malaysian Scelimena grasshoppers

Article Title: Towards a better understanding of the genus Scelimena ( Orthoptera , Tetrigidae , Scelimeninae ): New insights and notes on the taxonomy, ecology, and physiology of the genus in Peninsular Malaysia

Article References: Muhammad, A. A., Deranja, M., Adžić, K., & Abdullah, N. A. (2023). Towards a better understanding of the genus Scelimena (Orthoptera, Tetrigidae, Scelimeninae): New insights and notes on the taxonomy, ecology, and physiology of the genus in Peninsular Malaysia. Journal of Orthoptera Research, 32(1), 55-62. https://doi.org/10.3897/jor.32.91153

Image Credits: AI Generated

DOI: 10.3897/jor.32.91153

Keywords: Scelimena gombakensis, Falconius dubius, pygmy grasshoppers, Tetrigidae, Peninsular Malaysia, taxonomic revision, citizen science, scanning electron microscopy, aquatic adaptations, species distribution, Towards, better