Butterfly Biodata:
Genus: Rapala Moore, 1881
Species: cowani Corbet, 1939
Wingspan of Adult Butterfly: 31-33mm
Caterpillar Local Host Plant: Xylocarpus granatum (Meliaceae, common names: Mangrove Cannonball Tree, Nyireh Bunga, 木果楝).
Physical Description of Adult Butterfly:
On the underside, the markings on both forewing and hindwing are common in most Rapala spp., featuring a cell-end bar, a black post-discal band and indistinct submarginal fascia. The male is pale greyish brown while the female is pale greyish. On the hindwing, an orange-crowned black marginal spot is present in space 2 and on the tornal lobe. Between the two spots, the marginal area in space 1b is covered with pale bluish silvery scales. There is a white-tipped black tail at the end of vein 2. On the upperside, the male is bright orange-red with very broad dark brown borders on both wings, and the female is yellowish brown with brown border on the forewing. As with other Rapala spp., the male has in its hindwing a prominent oval-shaped brand at the base of space 7, and a secondary brand at the base of vein 6.
Field Observations:
The Cowan's Flash is rare in Singapore. Since its discovery in 1938 at the mouth of Sungei Jurong, no sightings have been reported for several decades in the mainland. Its recent sightings are confined to mangrove areas in Pulau Ubin and Sungei Buloh Wetland Reserve, in the vicinity of its larval host plant. The adults are fast flyers and take rapid flights among foliage at the water edge.
Early Stages:
Thus far, only one local larval host plant, namely, Xylocarpus granatum, a mangrove plant, has been confirmed. The caterpillar of the Cowan's Flash has also been found feeding on leaves of another mangrove plant, Allophylus cobbe, but did not survive till the adult stage. Hence further observations are required for the confirmation of this second plant.
On the host plant, caterpillars of the Cowan's Fash feed on young leaves and young stems. In the 1st to the 4th instar, the caterpillar feeds by grazing the leaf surface. At times in the 4th instar and in the entire 5th intar, the caterpillar switches to feeding along the leaf edge. In their natural habitats, the caterpillars are typically found in the company of a species of small black ants in a symbiotic relationship.
The eggs are laid singly on the surface of a stem of the host plant, usually on or near a node. Each egg is about 0.8mm in diameter, 0.5mm in thickness and green in colour. It is burger-shaped with a depressed micropylar at the pole. The egg surface is covered in a finely reticulated pattern.
It takes about 3 days for the egg to hatch. The newly hatched is pale yellowish with moderately long dorsal and lateral setae. Its body has a length of about 1.6mm. Reddish brown patches can be seen on the 1st, 6th-8th abdominal segments and on the anal plate. It also has a black prothoracic shield and a black head. After about 2 days of growth in the first instar, and reaching a length of about 2.6mm, the caterpillar moults to the next instar.
The 2nd instar caterpillar has dark reddish brown patches on the thoracic segments, as well as in the 1st, 6th-8th abdominal segments. There are also two brown spots on the anal plate. From above, the 7th to 10th segments appear to have fused together to form a saucer-like structure. The dorsal nectary organ on the 7th abdominal segment is now discernible. There are short black setae emanating from rows of conical projections occurring dorso-laterally. Numerous pale yellowish short setae occur sub-spiracularly along the body fringe. The 2nd instar caterpillar reaches a length of about 4.2mm, and after about 2 days in this stage, it moults again.
The 3rd instar catepillar resembles the 2nd instar caterpillar closely, but with the hair-like setae replaced by paddle-like setae. These paddle-like setae are brown to black for those occuring dorso-laterally and on the posterior segments, while remaining ones along the body fringe are pale yellowish brown. On the 7th abdominal segment, the dorsal nectary organ is now more readily observed. The 3rd instar takes about 3 days to complete with the body length reaching about 8.5-9mm before the next moult.
The 4th instar caterpillar has a more strking appearance, featuring broad triangular to semi-circular yellowish green or pale yellowish brown dorsal markings on the 2nd to 5th abdominal segement, and brown to dark brown lateral patches on almost all body segments. All body setae, whether occuring dorso-laterally or along body fringe are now much shorter in proportion to the size of the body segments. Tentacular organs on the 8th abdominal segments can now be easily observed being everted from time to time. The 4th instar takes about 3 days to complete with the body length reaching 13.8 to 14mm.
The 5th and final instar caterpillar is much larger with increases in both body length and width. It has similar markings as in the previous instar. In this instar, the caterpillar mostly feeding along the leaf edge.
After about 3 to 4 days of feeding and reaching a length of about 22mm, the caterpillar stops food intake and wanders around for a pupation site. During this time, its body gradually shortened and body color darkens. Typically the caterpillar chooses a concealed space in a leaf litter for its pupation site.
The pre-pupatory caterpillar prepares for pupation by spinning a silk girdle and a silk pad to which it attaches itself via anal claspers. After about 1 day as a pre-pupa, pupation takes place. The pupa has a shape typical of most lycaenid species with a length of 13.8-14.2mm. It is pale reddish to yellowish brown in base colour, and its surface bears numerous small dark speckles.
Eight to nine days later, the pupa darkens, first in the wing pad and thorax, then progressively in the abdomen. The presence and absence of the reddish patch in the wing pads gives an early indication of the sex of the soon-to-emerge adult. The next day, the pupal stage comes to an end with the emergence of the adult butterfly.
Video: A female Cowan's Flash emerging from its pupal case.
Video: A male Cowan's Flash emerging from its pupal case.
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.
- Biodiversity Record: Rediscovery of the butterfly, Rapala cowani, on Singapore Island, Loh J, Low JK & Soh ZS-H, Nature in Singapore, 15: e2022113. DOI: 10.26107/NIS-2022-0113, 2022.
I would like to express my gratitude to Lim Cheng Ai and Sebastian Ow for sharing sighting information of an ovipositing Cowan's Flash and identification of the larval host plant.
Text by Horace Tan, Photos by Sebastian Ow, Lim Cheng Ai, Low Jian Kai, Loh Mei Yee, Khew SK and Horace Tan, Videos by Loh Mei Yee and Horace Tan.
Wonderful article and images,,,,THankyou for sharing
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