The Green Oakblue (Arhopala eumolphus maxwelli)
A male Green Oakblue sunbathing with opened wings showing its coppery green uppersides
All too soon, we are almost at the end of the first half of the year 2024. The nature community in Singapore celebrated Pesta Ubin and Ubin Day. In its ninth edition, the event aims to share the essence of a sustainable and conservation-driven “Live Kampung” in harmony with nature, foster deeper affection and appreciation for Ubin’s heritage and ecosystem and solidify the island’s position as a premier “place-based” learning destination, offering enriching educational experiences for all ages.
The recent oil spill incident on 14 Jun is a grim reminder of how delicate our natural environment is. The spill that was sparked by Netherlands-flagged dredger Vox Maxima hitting Singapore-flagged bunker vessel Marine Honour at Pasir Panjang Terminal released about 400 tonnes of low-sulphur fuel into the sea. The impact of the spill could adversely affect organisms living on or near the water's surface such as sea birds, mangrove forests and corals could be smothered by the oil slick and these organisms end up ingesting toxic chemicals.
This month, we feature one of the Oakblues or Arhopala spp. as our Butterfly of the Month for June 2024. The Arhopala genus comprises close to over a hundred species in Malaysia and Singapore - many of which are cryptic and challenging to identify confidently due to their near identical appearances. Most prefer heavily shaded forest habitats and stay close to the ground where they perch on the uppersides of foliage.
A male Green Oakblue sunbathing showing its coppery green uppersides
The uppersides of the majority of the species are iridescent purple or blue in both sexes, with the exception of a few where the males are a metallic green. The Green Oakblue (Arhopala eumolphus maxwelli), our Butterfly of the Month, is one such species. The male of the Green Oakblue is a brassy green on the upperside, with the forewing border decreasing from 2.0 mm at the tornus to 1.0 mm at the apex. When viewed at different angles, the upperside takes on changing shades of green and can even appear bluish at certain oblique angles.
A female Green Oakblue sunbathing showing her purple-blue uppersides
The female is purple blue, and on the upperside of the forewing, the border usually reaches the apex of the cell. The Green Oakblue features a white tipped tail originating from vein 2 of the hindwing. The species of the eumolphus group have the postdiscal spot in space 4 on the underside of the forewing moved out of line with the adjacent spots above and below it.
The butterfly has a strong flight and takes off to the treetops in a very capable fashion if disturbed. At other times, it flies from perch to perch in the forest undergrowth and stops on the tops of leaves with its wings folded upright. At certain hours of the day, both sexes may be encountered with their wings opened to sunbathe in the warm sunshine.
A Green Oakblue feeding on the ripened fruit of the Singapore Rhododendron
The Green Oakblue is rarely observed to feed on flowering plants or puddling, but is occasionally drawn to the ripened fruits of the Singapore Rhododendron (Melastoma malabathricum) growing along the forest edges. The caterpillar host plant in Singapore is Lithocarpus elegans and the caterpillars are attended to by at least 2 species of ants, of which Polyrachis sp. is the one more often encountered.
Text by Khew SK : Photos by Khew SK, Koh CH, Jonathan Soong and Horace Tan
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