Butterfly Biodata:
Genus: Rapala Moore, 1831
Species: manea Hewitson, 1863
Subspecies: chozeba Hewitson, 1863
Wingspan of Adult Butterfly: 32-36mm
Caterpillar Local Host Plants: Dendrolobium umbellatum (Fabaceae, common names: Dendulang, Petai Belalang, Petai Laut, Sea Dendrolobium, 伞花假木豆), Bridelia tomentosa (Phyllanthaceae, common names: Pop-gun Seed, 土蜜树), Trema tomentosa (Ulmaceae, common names: Rough Trema, Poison Peach, 山黄麻), Acacia auriculiformis, (Fabaceae, common names: Common Acacia, Earleaf Acacia, 大叶相思 , 耳叶相思), Nephelium lappaceum (Sapindaceae, common names: Rambutan, 红毛丹), Dimocarpus longan (Sapindaceae, common names: Longan, 龙眼), Sterculia oblongata R. Br. (Malvaceae, common names: Sterculia, Kalumpang), Melastoma malabathricum L. (Melastomataceae, common names: Singapore Rhododendron, 野牡丹).
Physical Description of Adult Butterfly:
On the upperside, the wings are unmarked with the male appearing in deep blue and the female steely blue. On the underside, both sexes are pale brown. A faint purple wash can be seen in pristine specimens. The markings are typical for Rapala spp, with cell-end bars on both wings, and narrow brown postdiscal bands. The hindwing carries a white-tipped filamentous tail at the end of vein 2 with a tornal lobe between veins 1a and 1b. In addition, there is a black tornal spot, an extensive bluish green patch (reaching up to the postdiscal striae) in space 1b, an orange-crowned black sub-marginal spot in space 2.
Field Observations:
The Slate Flash is moderately common in Singapore. It is usually found in urban parks, nature corridors, curated gardens, and forested areas within the catchment nature reserves. The fast-flying adults have been sighted taking nectar at flowering plants, and sunbathing with fully opened wings on sunny days.
Early Stages:
Across the distribution region of the Slate Flash, a number of larval host plants have been identified. In Singapore, thus far eight plants from multiple families have been recorded as the larval hosts for the Slate Flash. On these plants, early stages of the Slate Flash typically feed on flower buds, flowers, developing fruits, and in some cases, young leaves on growing shoots. The caterpillars are attended by ants in all stages.
Eggs of the Slate Flash are typically laid singly among flower buds of the host plant.
Each egg is about 0.6mm in diameter, white with a strong greenish tinge when freshly laid. It is bun-shaped with a depressed micropylar at the pole and a surface reticulated with rather large polygonal depressions.
It takes about 3 days for the egg to hatch. The young caterpillar consumes just enough of the egg shell to emerge. The newly hatched is pale yellowish brown with long dorsal and lateral setae. Its body has a length of about 1mm. Pale reddish brown patches can be seen on the dorsum of the metathorax, 1st, 6th-8th abdominal segments. It also has a black prothoracic shield and a black head. After about 2-3 days of growth in the first instar, and reaching a length of about 2mm, the caterpillar moults to the next instar.
The 2nd instar caterpillar is pale yellowish brown in base color and has dark reddish brown patches on the dorsum of the metathorax, as well as in 6th-8th abdominal segments. There are short black setae emanating from rows of whitish conical projections occurring dorsally and laterally. The 2nd instar caterpillar reaches a length of about 3.5mm, and after about 2-3 days in this stage, it moults again.
In the 3rd instar, the markings on the dorsum of the caterpillar resemble those in the 2nd instar. The body base colour can either be greenish or reddish brown, depending on the host plant the caterpillar resides on. The dorsal nectary organ on the 7th abdominal segment and the tentacular organs on the 8th abdominal segment are now easily discernible.
As the body grows to a length of around 5.5mm, the caterpillar stops feeding and comes to rest at a spot on the stem to prepare for the next moult. After about 2-3 days in the 3rd instar, the moult to the 4th and penultimate instar takes place.
The 4th instar caterpillar resembles the 3rd instar caterpillar in most body features/markings, and is generally pale brown or pale greenish. In some specimens, the brownish dorsal patch on the dorsum is prominently featured. Whitish to pale chevron markings are also much more distinct on the side of the dorsum in this instar. In addition, tentacular organs on the 8th abdominal segment can now be easily observed being everted from time to time. The 4th instar takes about 2.5-3 days to complete with the body length reaching up to 10mm.
The 5th instar caterpillar resembles the 4th instar caterpillar in most body features/markings. Depending on the host plant being utilized, the body base colour can be green, yellowish, brown, and reddish. Dark reddish brown patches on the metathorax and 6th-8th abdominal segments can be present or absent. The 5th (and final) instar lasts about 3-4 days with the body length reaching up to 17-19mm.
As it enters the pre-pupatory phase of its life cycle, the caterpillar ceases its feeding activity. Its body gradually shrinks in length and the colour darkened. The pre-pupatory caterpillar wanders around in its quest for a suitable pupation site. Typically it settles for a spot on a surface which is partially concealed. At the chosen pupation site, it stays dormant for a period of time before spinning a silk pad and then attaches itself to it via claspers at the posterior end.
About 1 day after the pre-pupatory caterpillar secures itself to the pupation spot, pupation takes place. The pupa is held firmly via its cremaster to the silk pad on pupation spot. It is 10-11 mm in length, with the typical shape for a lycaenid pupa. It is reddish brown to yellowish brown in base colour, and its surface bears numerous small dark speckles and short setae.
Six to seven days later, the pupa becomes darkened in color signaling the imminent emergence of the adult. The next day the adult butterfly emerges from the mature pupa.
References:
- [C&P5] The Butterflies of The Malay Peninsula, A.S. Corbet and H.M. Pendlebury, G. and N. van der Poorten (Eds.), 5th Edition, Malayan Nature Society, 2020.
- Butterflies of Thailand, Pisuth Ek-Amnuay, 2nd Edition, 2012.
- A Field Guide to the Butterflies of Singapore, Khew S.K., Ink On Paper Communications, 2nd Edition, 2015.
I would like to express my gratitude to Mr Hanpeng Lim for sharing information on the host plant and early stages of the Slate Flash.
Text by Horace Tan, Photos by James Chia, Koh Cher Hern, Lim Hanpeng, Loh Mei Yee, Loke PF, Khew SK and Horace Tan.
