A list of the butterflies of Mt. Penrissen, Sarawak, with notes on the species
R.S. Shelford published this faunal account in 1901, reporting on butterflies collected in May 1899 at elevations of 2,800 to 4,200 feet on Mount Penrissen, Sarawak. The paper argues that the mountain’s dense, uncleared jungle produces a comparatively sparse but taxonomically distinctive lepidopteran fauna, with several species absent from the more frequently studied nearby peaks of Matang and Santubong.
Summary
Shelford’s primary objective is to document the butterfly fauna of Mount Penrissen and to situate it within the broader biogeographical context of the Kuching mountain group. He observes that butterflies on Penrissen were markedly less numerous than on Matang and Santubong, attributing this to the “very rank and dense jungle” and the total absence of cleared spaces that characterise the latter two mountains (p. 29). Despite the lower overall abundance, the Penrissen collection contains several species never recorded from Matang or Santubong despite “the most careful and frequent collecting” there, lending the assemblage a distinctive character (p. 29). Shelford explicitly frames the mountain fauna as analogous to an insular fauna, a concept that anticipates later island biogeographical thinking.
The paper is interspersed with taxonomic and theoretical remarks. Shelford reassigns a species from the sub-genus Chittira to Parantica on the basis of androconial scales on the male forewing veins (p. 30). He raises the unresolved problem of the extreme sex-ratio disparity between Elymnias lowei (males abundant throughout Borneo, females extremely rare) and its continental topomorph E. rhadamanthus (females plentiful in the Malay Peninsula and Singapore), noting that the females of the two species differ more markedly from each other than do the males (p. 31). Two putative new species are identified from single female specimens—Elymnias aroa and an unnamed Biduanda relative—both deferred pending the acquisition of males (pp. 34–35).
The most extended theoretical passage concerns Lycaenid underside wing-pattern evolution. Shelford proposes that “the more highly organised the butterfly, the more the underside wing-pattern tends to disappear from the discs of the wings and concentrate at the margins and at the anal angle of the hind-wing” (p. 34). He links this to a general principle of defensive specialisation: as discal patterns fade, the marginal eyespot becomes relatively more conspicuous, directing predator attacks away from vital body parts, while the unornamented disc reduces the risk of attracting attention to the body itself (pp. 34–35). He illustrates the continuum with Loxura atymnus, in which the eyespot is replaced entirely by hindwing tails.
Key Findings
- The Penrissen collection was made in May 1899 at elevations of 2,800–4,200 feet; Shelford considers the list “fairly complete” for that season (p. 29).
- Several species in the Penrissen assemblage had never been recorded from Matang or Santubong despite extensive prior collecting on those mountains (p. 29).
- Elymnias lowei males are abundant throughout Borneo while females are “extremely rare”; the converse holds for the continental topomorph E. rhadamanthus in the Malay Peninsula and Singapore (p. 31).
- A new species, Elymnias aroa, is identified from two female specimens; description is deferred pending a male (p. 34).
- A second putative new species, related to Biduanda thesmia and B. lavitsoni, is identified from a single female; description likewise deferred (p. 34).
- The female of a Delias species originally described from Kina Balu is described for the first time, with a wingspan of 88 mm; the species is notably omitted from Butler’s 1897 revision of the genus (p. 35).
Conclusion
Shelford’s definitive takeaway is that Mount Penrissen, despite its lower overall butterfly abundance, harbours a taxonomically distinct fauna that cannot be predicted from the better-known nearby mountains, reinforcing the principle that each mountain in the Kuching group functions as a biogeographical unit with its own endemic or near-endemic component. The paper also contributes a working hypothesis on the evolutionary trajectory of Lycaenid underside patterns that, while framed in the language of 1900s natural history, anticipates modern understanding of aposematic and deflectionary signalling.
Context
- Shelford was a British civil servant and amateur entomologist serving in the Sarawak administration; the paper reflects the colonial-era practice of government officials producing natural-history contributions to the Journal of the Straits Branch of the Royal Asiatic Society.
- The comparative table (pp. 37–41) draws on the Sarawak Museum collection and prior literature, situating the Penrissen data within the existing Kuching mountain-group faunal record.