Dermaptera

The available record on Dermaptera (earwigs) in the Society’s literature is limited to a single taxonomic account of the Mentawai Islands, off the west coast of Sumatra, and the following synthesis is confined to that evidence. Borelli’s 1926 paper documents 22 species collected during a September–November 1924 expedition to Siberut and Sipora, two of them new to science, and uses the assemblage to argue that the Mentawai Group constitutes a zoologically distinct entity separated from Sumatra by deep-water basins rather than the shallow Sunda shelf [1, pp. 384–391].

Biogeographical Context

The Mentawai Group—comprising Siberut, Sipora, and North and South Pagi—lies parallel to the west coast of Sumatra, approximately 90–110 kilometres distant. Kloss, who introduced the paper as Director of Museums for the Straits Settlements and Federated Malay States, noted that the islands are mostly swamp with hills nowhere exceeding 500 metres, and that the terrain is difficult to traverse owing to soft ground and frequent flooding [1, p. 385]. The group is surrounded by water 200–1,000 metres deep, and the long Mentawai Basin between it and Sumatra reaches 1,000–2,000 metres, placing it well beyond the shallow Sunda shelf (less than 75 metres) on which stand almost all the landmasses of Malaysia [1, p. 386]. Kloss argued that, whatever the precise bathymetry, the faunas of the groups differ greatly and that the Mentawai Islands, in spite of their small size and lack of height, are zoologically quite as distinct from each other and from the rest of Malaysia as the larger areas of that sub-region are from one another [1, p. 386].

Taxonomic Findings

Borelli, working from material held at the Raffles Museum, Singapore, and the Zoological Museum at Buitenzorg, described two new species: Diplatys karnyi (a protodermapteran of the family Pygidicranidae, male body length 11.5 mm) and Nesogaster gonopygius (an eudermapteran of the family Labiidae, male body length 4.5 mm) [1, pp. 387–391]. The remaining 19 species were already known, most of them common throughout the Malay Archipelago. Notably, Tagalina semperi Dohrn had not previously been encountered in Sumatra or Java, and Proreus delicatulus, originally described from Ceylon, had been recovered only from Sumatra before this expedition [1, p. 387]. Chelisoches semirufus Borelli, described from the same material, was represented by multiple specimens from both Sipora and Siberut and constituted the only known examples of the species at the time of publication [1, p. 391].

A point of unresolved discrepancy concerns the earlier collections of Dr. Elia Modigliani, preserved in Genoa, from which seven Dermaptera species had been reported for the Mentawais. None of these seven was recovered by the 1924 party, a gap Borelli records without attempting to explain [1, p. 387].

Research and Documentation

The Dermaptera account forms part of the broader “Spolia Mentawiensia” series, a multi-author, multi-journal synthesis of the island group’s natural history published in 1926. Companion volumes covered flora (Ridley), birds (Chasen and Kloss), reptiles and amphibians (Smith), and Zoraptera (Karny) [1, p. 386]. The expedition was undertaken by Kloss, accompanied by N. Smedley (Assistant Curator, Raffles Museum) and H. H. Karny (Assistant Entomologist, Buitenzorg), with a party of native collectors, and was made possible by the assistance of the Government of the Netherlands East Indies [1, p. 385]. As the first systematic faunal survey of the Mentawai Dermaptera, the paper established a baseline against which future collections could be compared, though the Modigliani discrepancy and the absence of subsequent Mentawai earwig records in the Society’s literature suggest that the group has remained under-studied in this respect.

MBRAS Sources

• A. Borelli (1926). Spolia mentawiensia: Dermaptera. Introd. C.B. Kloss. JMBRAS 4(3): 384–391

References

1. A. Borelli (1926). Spolia mentawiensia: Dermaptera. Introd. C.B. Kloss JMBRAS 4(3): 384–391. Read on JSTOR