A Butterfly Labelled in Malaysia Was Really from Brazil: Solving a 140-Year Taxonomic Mistake

A small blue butterfly described in 1884 from specimens collected during one of the most famous oceanographic voyages in history has spent more than a century filed under the wrong species — and, as it turns out, on the wrong side of the planet. New research published in the journal Nota Lepidopterologica shows that Catochrysops trifracta, a name described by the British entomologist Arthur Butler and long treated as a synonym of the widespread Old World butterfly Euchrysops cnejus, actually belongs to Hemiargus hanno, a lycaenid butterfly native to South America and the Caribbean. The correction untangles a geographic error that dates back to the Challenger expedition and restores the proper identity of a species that has been hiding in plain sight in museum drawers for nearly 140 years.

The story begins with HMS Challenger, the Royal Navy vessel whose four-year circumnavigation from 1872 to 1876 laid the foundations of modern oceanography. Along the way, the expedition’s naturalists collected butterflies at various ports of call, and some of that material reached Butler at the British Museum. In 1884 he described Catochrysops trifracta on the basis of two damaged male specimens, citing the type locality as Rat Island in the Strait of Malacca, collected on 1 September 1873. Butler noted that his material also came from the islands of St. Thomas and Bermuda in the New World, alongside the Old World localities of Ké Dulan, Ternate and Amobina, but he anchored the new species firmly in Southeast Asian waters.

His description pointed to a butterfly resembling the gram blue, Euchrysops cnejus, in the pattern of its underside, but with a distinctive difference: the row of spots across the forewing disk was broken into three parallel oblique dashes edged in white, rather than forming a single slightly irregular stripe. He also recorded only one subanal black spot on the hindwing with a pale yellow zone, barely touched with metallic scales, and a wingspan of 23 to 28 millimetres. Those characters, as the new study demonstrates, were accurate observations of the specimens — but they describe a Neotropical butterfly, not a Malayan one.

Over the following decades the name drifted through the literature in inconsistent ways. Butler himself later moved C. trifracta, along with C. cnejus and several other species distinguished by having smooth rather than hairy eyes, into his new genus Euchrysops in 1900, with C. cnejus as the type species. The species was briefly mentioned in Swinhoe’s Lepidoptera Indica in 1910 as a Malayan species allied to Indian forms. Yet the major synonymic catalogues of the era told a different story: de Nicéville in 1890 and Seitz in 1927 listed the synonyms of Euchrysops cnejus without including trifracta, Bethune-Baker’s 1923 revision of Catochrysops ignored it entirely, and even the standard reference Butterflies from the Malay Peninsula, first published by Corbet and Pendlebury in 1934, never mentioned it. The name effectively vanished from active use before reappearing, without apparent justification, as a synonym of E. cnejus in Seki and colleagues’ 1991 work on Malaysian butterflies — a listing subsequently copied by Bridges in 1994 and absorbed into most online databases.

The key to the mystery lay in the original labels and in a footnote that had been overlooked. The two syntypes of Catochrysops trifracta are preserved in the Natural History Museum in London, both bearing locality labels that read simply Rat Island — with no mention of the Malaccas at all. Thomson and Murray, in their official 1885 report on the Challenger expedition, had already flagged the problem in a footnote on page 214: the locality information given by Butler was incorrect, and the specimens actually came from Ilha Rata — Rat Island — in the Fernando de Noronha archipelago off the coast of Pernambuco, Brazil. Curiously, the same report still suggested the species seemed to be of Malayan origin, a contradiction that apparently discouraged later researchers from pursuing the point.

Fernando de Noronha’s butterfly fauna makes the South American explanation overwhelmingly likely. In their 1890 work on the natural history of the archipelago, Kirby and Ridley reported that Hemiargus hanno — then treated under the name Taurucus hanno — a lycaenid widely distributed across South America, was frequent on Rat Island and the main island. Indeed, that species appears to be the only butterfly occurring anywhere in the archipelago, according to a 1962 survey by Alvarenga. Kirby even acknowledged that the expedition’s C. trifracta had not been found again on the islands, but suggested this could reflect mislabelling of the specimens, since the genus was otherwise known only from the East Indies. Butler, meanwhile, seems to have been unaware of both the Thomson and Murray footnote and the Ridley and Kirby account when he revised his genus in 1900.

To settle the question definitively, the author of the new study compared the syntype specimens directly with reference material of both candidate species, drawing on holdings including a non-type specimen of Hemiargus hanno from Venezuela at the McGuire Centre for Lepidoptera and Biodiversity in Florida, and a non-type Euchrysops cnejus from the Philippines. The morphological evidence turned out to be unambiguous. Like H. hanno, the C. trifracta syntypes bear only a single black tornal spot on the hindwing — exactly the feature Butler described as only one subanal black spot — accompanied by blue scaling toward the margin and a small amount of orange on the inner margin. Euchrysops cnejus, by contrast, has two black tornal spots with blue scaling, each with a larger amount of orange, and these spots are visible on the upper side in both sexes, whereas the single tornal spot of H. hanno and C. trifracta is barely discernible from above.

Further characters reinforce the distinction. Euchrysops cnejus carries a tail in the tornal area of the hindwing, a feature entirely lacking in both H. hanno and the trifracta syntypes. And both H. hanno and the Challenger specimens share a grey sub-basal spot at the base of the ventral hindwing cell Cu2-2A that is absent in E. cnejus — although that spot does occur in the widespread Afrotropical species E. malathana and its arid-adapted sister species E. nilotica. Taken together, the wing pattern, tornal structure and presence of the tail tell a consistent story: the syntypes represent Hemiargus hanno and neither E. cnejus nor any other member of Euchrysops.

On these grounds the study formally places Catochrysops trifracta Butler, 1884 as a junior subjective synonym of Hemiargus hanno (Stoll, 1790), with the status revised from its previous placement. Because the name trifracta was based on two syntypes and its identity needed to be fixed permanently, the author designated a lectotype: the better-preserved of the two male specimens in the Natural History Museum, London, carrying the labels Type; Rat Island 84 · 10; Catochrysops trifracta type Butler; and the registration number NHMUK010588635. A new lectotype label recording the 2022 designation will be added to the specimen in due course. This act of type designation is a standard taxonomic procedure that pins the name unambiguously to a single physical specimen, preventing future confusion.

Beyond resolving one dangling name, the case is a vivid illustration of how much biology still sleeps inside historical museum collections. The Challenger expedition’s butterflies sat mislabelled for more than a century while the same species thrived in the wild on the very islands where it was originally caught — only under a different name. The study also highlights how errors propagate through the taxonomic literature: a synonymy introduced in a 1991 field guide became entrenched in catalogues and databases simply by repetition. Correcting the record matters practically as well as academically, because Euchrysops cnejus is an Old World species and Hemiargus hanno a New World one; conflating them distorts biogeographic inference, ecological interpretation and conservation assessment alike. With the lectotype now designated and the wrong-continent error corrected, one of oceanography’s most celebrated expeditions has, at last, had its butterfly placed where it truly belongs.

Subject of Research: Taxonomic revision showing the butterfly name Catochrysops trifracta Butler, 1884 is a synonym of the Neotropical species Hemiargus hanno

Article Title: On the wrong continent: The identity of Catochrysops trifracta Butler, 1884 ( Polyommatinae , Lycaenidae ), currently a synonym of Euchrysops cnejus (Fabricius, 1798)

Article References: Espeland, M. (2022). On the wrong continent: The identity of Catochrysops trifracta Butler, 1884 (Polyommatinae, Lycaenidae), currently a synonym of Euchrysops cnejus (Fabricius, 1798). Nota Lepidopterologica, 45, 129-132. https://doi.org/10.3897/nl.45.81499

Image Credits: AI Generated

DOI: 10.3897/nl.45.81499

Keywords: taxonomy, Lepidoptera, Lycaenidae, Catochrysops trifracta, Hemiargus hanno, Euchrysops cnejus, Challenger expedition, Fernando de Noronha, lectotype designation, museum specimens, biogeography, Nota Lepidopterologica