Life History of the Scarlet Flash

Life History of the Scarlet Flash (Rapala dieneces dieneces)

Butterfly Biodata:
Genus: Rapala Moore, 1881
Species: Species: dieneces Hewitson, 1878
Sub-species: dieneces Hewitson, 1878
Wingspan of Adult Butterfly: 15-18mm
Caterpillar Local Host Plants: Bridelia tomentosa (Phyllanthaceae, common name: Pop-gun Seed, 土蜜树), Prunus polystachya (Rosaceae), Trema tomentosa (Ulmaceae, common name: Rough Trema, Poison Peach), Mallotus paniculatus (Euphorbiaceae, common name: Turn-in-Wind), Ixora sp. (Rubiaceae), Syzygium sp. (Myrtaceae).

A male Scarlet Flash.

A female Scarlet Flash.

Upperside view of a male Scarlet Flash.

Physical Description of Adult Butterfly:
On the upperside, the female is entirely brown whereas the male is deep red with broad black border on the forewing, while the hindwing is shaded with black at the cell area and tornal margin. As with other Rapala spp., the male has an oval-shaped brand in space 7 on the hindwing. On the underside, both sexes are ochreous or pale brown. The markings are typical for Rapala spp, with cell-end bars on both wings, and narrow brown postdiscal band edged with white on the side nearer to the termen. 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, a bluish green patch in space 1b, an orange-crowned black sub-marginal spot in space 2, and black post-discal striae in spaces 1b and 2.

A female Scarlet Flash.

Upperside view of a female Scarlet Flash.

Field Observations:
The Scarlet Flash is moderately rare in Singapore. It is mainly found in the forested areas of the nature reserves. The adults are fast flyers and take rapid flights among foliage at the forest edges. At times, adults come at rest on flowers for their nectary intakes.

A female Scarlet Flash taking nectar from flowers blooming along a forest edge.

Another female Scarlet Flash seen perching on a leaf.

Early Stages:
The Scarlet Flash is polyphagous as its early stages feed on a number of host plants from different families. Locally six plants, Bridelia tomentosa, Prunus polystachya, Trema tomentosa, Mallotus paniculatus, a Syzygium sp. and an Ixora sp., have so far been identified as the larval hosts. The caterpillars of the Scarlet Flash feed on the flowers, flower buds, young and tender leaves of the host plants. In the wild, the caterpillars are typically found in the company of small black ants.

Local host plant #1: Bridelia tomentosa.

Local host plant #2: Trema tomentosa.

Local host plant #3: Prunus polystachya.

Local host plant #4: Mallotus paniculatus.

Local host plant #5: Red Ixora.

Eggs are laid singly on a leaf, a part of an inflorescence or a flower of the host plant. Each egg is about 0.5-0.6mm in diameter, greenish in colour when freshly laid. It is bun-shaped with a depressed micropylar at the pole and a surface reticulated with very fine ridges.

A female Scarlet Flash attempting to oviposit on an inflorescence of the Red Ixora.

Two close-up views of an egg of the Scarlet Flash.

Two views of a fully developed egg of the Scarlet Flash.

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 1.2mm. Pale 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. As it feeds and grows in this instar, the brownish patches darkened gradually. After about 3 days of growth in the first instar, and reaching a length of about 2.2mm, the caterpillar moults to the next instar.

1st instar caterpillar, a few hours after hatching, length: 1.3mm.

Two views of a 1st instar caterpillar of the Scarlet Flash, length: 2.1mm.

Two views of a late 1st instar caterpillar of the Scarlet Flash, dormant prior to its moult.

The 2nd instar caterpillar is pale yellowish brown in base color and 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 4mm, and after about 3 days in this stage, it moults again.

Two views of an early 2nd instar caterpillar, length: 2.2mm.

Two views of a 2nd instar caterpillar of the Scarlet Flash, length:2.9mm.

Two views of a late 2nd instar caterpillar, dormant prior to its moult.

The 3rd instar caterpillar 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 occurring 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 8mm before the next moult.

Two views of an early 3rd instar caterpillar of the Scarlet Flash, length: 3.9mm.

Two views of a 3rd instar caterpillar of the Scarlet Flash, length: 6mm.

Two views of a late 3rd instar caterpillar of the Scarlet Flash, dormant prior to its moult, length: 7.5mm.

The 4th instar caterpillar has a more striking appearance, featuring broad yellowish green or pale yellowish brown dorsal band on the 2nd to 5th abdominal segment, and brown to dark brown lateral patches on almost all 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 4 days to complete with the body length reaching up to 14mm.

Two views of an early 4th instar caterpillar, length:8.5mm.

Two views of a 4th instar caterpillar, length: 13mm.

A a 4th instar caterpillar of the Scarlet Flash observed in the field, with ants in attendance.

Two views of a late 4th instar caterpillar, dormant prior to its moult.

The 5th instar caterpillar has similar markings as in the 4th instar with more contrasting coloration between the yellowish to greenish dorsal band on the middle segments and reddish brown to dark brown markings on the other body segments. It is not uncommon to see numerous ants attending to a 5th instar caterpillar in field observations.

Two views of a newly moulted 5th instar caterpillar.

Two view of a 5th instar caterpillar, length: 19.5mm.

Four 5th instar caterpillars of the Scarlet Flash being attended by ants on a branch of Trema tomentosa.

After about 5-6 days of feeding and reaching a length of about 20-21mm, 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.

Two views of a late 5th instar caterpillar of the Scarlet Flash with body color darkened.

Two views of a late 5th instar caterpillar with a darkened appearance and ants attending to it.

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 11-12.5mm. It is pale reddish to yellowish brown in base colour, and its surface bears numerous small dark speckles.

Two views of a pre-pupa of the Scarlet Flash.

Two views of a pupa of the Scarlet Flash.

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.

Two views of a mature pupa of the Scarlet Flash.

A newly eclosed male Scarlet Flash.

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.

Text by Horace Tan, Photos by Ash Foo, Loh Mei Yee, Khew SK, Koh Cher Hern, Jonathan Soong and Horace Tan.

Butterfly of the Month - August 2024

Butterfly of the Month - August 2024

The Singapore Four Line Blue (Nacaduba pavana singapura)

A couple more hours, and August 2024 will come to an end. August is the month when Singapore celebrates its National Day. Every year since this 'little red dot's' independence from Malaysia in 1965, Singaporeans of all walks of life come together to watch the parade at various designated locations in Singapore. It is a day of celebrations and pride as Singaporeans and residents wish the nation a happy birthday.

This year, 2024, Singapore celebrated its 59th year of independence. It was also a special year that marked the appointment of Singapore's fourth prime minister - Mr Lawrence Wong, who took over from former PM Lee Hsien Loong, who was prime minister from 2004 - 2024. It was also the first year that PM Lawrence Wong shared his vision for Singapore in his inaugural National Day Rally.

A Singapore Four Line Blue feeding on the flower of the Red Bush (Leea rubra)

It is therefore apt that, as a nation celebrates its 59th birthday, that we feature a small butterfly that carries the word 'singapura' in its taxonomic name - the Singapore Four Line Blue (Nacaduba pavana singapura). This small Lycaenidae that carries the subspecies name referring to Singapore, is one of the members of the 4-line blues of the genus Nacaduba.

The Singapore Four Line Blue has been described as "with a pale greyish blue male, and is seldom seen except in Singapore, where it is sometimes quite common on the landward edge of mangrove swamps."Indeed this is the case, where the species is a regular at the Sg Buloh Wetland Reserve (SBWR), Kranji Nature Trail and Mandai Mangroves where its caterpillar host plants Derris trifoliata (Leguminosae), Andira inermis (Leguminosae), Allophylus cobbe (Sapindaceae) grow quite commonly.

A female Singapore Four Line Blue with partially opened wings showing the uppersides of the wings

The butterfly is rather small, with a wingspan of usually less than 20mm. Above, the male is greyish blue with a thread-thin border; the female is brown with a pale blue discal patch on the forewing and blue dusting on the basal part of the hindwing. The species belongs to the pavana group of the genus - a primary characteristic being the lack of a pair of sub-basal lines on the underside of the forewing.

Underneath, both sexes are greyish brown with the bands composed of a double series of whitish striae inwardly lined with darker lines with the space between them appear to be paler than the ground colour. On each hindwing, there is an orange-crowned tornal spot lightly speckled with bluish-green metalic scaling. Next to the tornal spot, a pair of filamentous white-tipped tails occurs at end of vein 2. Marginal and submarginal spots are black and stand out against the ground colour of greyish brown.

The Singapore Four Line Blue is skittish and flies erratically as it searches for food or, in the case of the female, is looking for its caterpillar host plants to oviposit. It is alert and is difficult to photograph in the field due to its small size and erratic flight. However, when it is busy ovipositing or occasionally stopping to feed at flowering plants, it gives a fair chance for a determined butterfly photographer to get a good shot of it.

A female Singapore Four Line Blue ovipositing.

A Singapore Four Line Blue feeding on the flower of the Pig's Grass (Synedrella nodiflora)

Males of the Singapore Four Line Blue are seldom seen to puddle, like several of its other cousins in the genus Nacaduba. They are more often spotted feeding at flowers like the females. The complete life history of the Singapore Four Line Blue has been successfully recorded in Singapore, and is recorded here on this blog. The caterpillars are polyphagous and feed on at least three different host plants usually found growing in back-mangrove habitats.

Text by Khew SK : Photos by Federick Ho, Khew SK, Low JK, Ong LM, Horace Tan and Angela Yeo.