Butterfly Biodata:
Genus: Nacaduba Moore, 1881
Species: hermus C. Felder, 1860
Subspecies: swatipa Corbet, 1938
Wingspan of Adult Butterfly: 27-30mm
Caterpillar Local Host Plant: Barringtionia racemosa (Lecythidaceae, common name: Common Putat, Fish-Killer Tree, Fish-Poison Tree, 水茄笗, 玉蕊).
Physical Description of Adult Butterfly:
As a member of the pavana group, the adult does not have a basal pair of lines in the underside forewing cell. Above, the male is violet blue (with a slightly frosted appearance) with a thread-thin border; the female is pale shining blue with broad brown borders. Underneath, both sexes are greyish brown with the bands (post-discal, discal and basal) composed of a double series of whitish striae inwardly lined with dark striae. Forewing postdiscal band is usually not dislocated at vein 6. On each hindwing, there is an orange-crowned tornal spot in space 2 lightly speckled with bluish-green metalic scales. Next to the tornal spot, a pair of filamentous white-tipped tails occurs at end of vein 2. Marginal and submarginal spots are dark greyish brown, and submarginal spots are mostly broadly lunulate. In the hindwing, the postdiscal band is usually close to the submarginal band.
Field Observations of Butterfly Behaviour:
The Pale Fourline Blue was recorded by early researchers in Singapore, but the species has been rarely sighted in the past two decades. However, in the second half of this year, sightings have increased markedly, thanks to the keen eyes of a few devoted young naturalists. These recent sightings are confined to the central and northern parts of the Singapore island where the local host plant, Barringtonia racemosa, is growing in abundance. The adults have been seen flying in the vicinity of the host plant, visiting flowering plants, puddling on wet grounds and performing oviposition rituals at developing inflorenscences of the host plant.
Early Stages:
The Pale Fourline Blue is polyphagous. In other countries/regions, plants such as Entada rheedii, Embelia subcoriacea and Nephelium lappaceum have been recorded as larval hosts. However, for Singapore, only one local host plant, Barringtonia racemosa, has thus far been recorded. The caterpillars of the Pale Fourline Blue mainly feed on flower buds of Barringtonia racemosa, but at times, also feed on the rachis and pedicel of the inflorescence. As in the case for most lycaenidae species, the caterpillars of the Pale Fourline Blue are tended by a number of ant species.
Eggs are laid singly on a flower bud or the rachis of an inflorescence of Barringtonia racemosa. It is not uncommon for a number of eggs to be found in the same inflorescence. Each egg is whitish with a green undertone. It has a thick discoid shape, and features a depressed micropylar on top. The egg surface is finely reticulated, slightly raised at the intersections of criss-crossing ridges. Th egg has a diameter of about 0.5mm.
It takes about 3 days for the egg to hatch. The young caterpillar consumes part of the egg shell to emerge. With a length of about 0.9mm, it has a pale yellowish body with long setae (hairs) dorsally and sub-spiracularly. The head is black in colour in this instar. The body color changes gradually to a brighter shade of yellow as growth progresses. The first instar lasts for 2-3 days and the body length reaches about 1.8mm before the moult to the 2nd instar.
In the second instar, dorsal setae are much shortened proportionately compared to those in the first instar. Moreover, there are numerous short setae present all over the body surface. The body color is mainly yellow with a hint of reddish brown in the anterior and posterior segments. In some individuals, the pale reddish brown coloration is more extensive. The 2nd instar lasts for 2-3 days and the caterpillar grows to a length of about 3.3mm to 3.5mm.
As in the 2nd instar, the 3rd instar caterpillar is yellowish with varying extent of pale reddish brown coloration on body segments. In most individuals, the pale reddish hue is present in the thoracic segments and the last 4-5 abdominal segments, as well as in the dorsum of first 4-5 abdominal segments. The prothoracc shield is whitish in color. The dorsal nectary organ and tentacular organs are also easily discernible. After 3 to 4 days in this instar with the body length reaching about 6.8-7mm, the next moult brings the caterpillar to its final instar.
The 4th instar caterpillar are similar to the 3rd instar caterpillar but with all red and reddish brown patches much more prominently marked and in strong contrast to the ground color. Some individuals can even be entirely reddish brown to pinky red in all body segments. As in the 3rd instar, the prothorcic shield is whitish and the dorsal nectary organ and tentacular organs are prominent on the posterior segments. Tentacular organs are readily everted when the caterpillar senses a threat (such as from a competing caterpillar) or when attending ants are present.
The 4th instar lasts for 3-4 days and the body grows up to a length of about 13-13.5mm. On the last day of this stage, the caterpillar ceases food intake and its body shrinks in length and decolorises to a dull shade of yellowish to pinky brown. The fully grown caterpillar finally comes to rest on a spot among leaves where it readies the site for pupation by spinning a silk pad and a silk girdle to secure itself.
About 0.75 day later, pupation takes place. The pupa has the typical lycaenid form, and is 9.6-10.2mm in length. It is mostly yellowish brown and speckled with black spots of various sizes and shapes.
Four to five days later, the pupa becomes darkened in color signaling the imminent emergence of the adult. The markings on the forewing upperside becomes increasing obvious through the pupal skin. 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.
- Kawthankar N, Nitin R, Balakrishnan VC, Churi PV, Kalesh S, Satya Prakash & Kunte K (2023) Larval host plants and other hosts of Indian butterflies. In Kunte K, Sondhi S & Roy P (eds.). Butterflies of India, v. 4.12. Indian Foundation for Butterflies. https://www.ifoundbutterflies.org/larval-hosts.
