Butterfly Biodata:
Genus: Polyura Billberg, 1820
Species: schreibers Linnaeus, 1758
Subspecies: tisamenus Fruhstorfer, 1911
Wingspan of Adult Butterfly: 60-80mm
Caterpillar Local Host Plants: Adenanthera pavonina (Fabaceae, common name: Red Saga), Nephelium lappaceum (Sapindaceae, common name: Rambutan), Acacia auriculiformis (Fabaceae, common name: Earleaf acacia), Ceiba pentandra (Malvaceae, common name: Silk-cotton Tree), Bruguiera cylindrica (Rhizophoraceae, common name: Bakau Putih).
Physical Description of Adult Butterfly:
The forewing has a strongly arched costa, a pointed apex and a concave termen. The hindwing has a pair of short stubby tails, longer and more pointed in the female. On the upperside, the Blue Nawab is brownish black with a whitish median band, broadly edged in blue, stretching across both wings. The white band is broader in the female. On the underside, the Blue Nawab is silvery white and is marked with bluish and brownish bands and spots.
Field Observations of Butterfly Behaviour:
Blue Nawab is moderately rare in Singapore. They can be found in urban parks, gardens, forested areas and mangrove wetlands. The adults are large-sized, heavy-bodies butterflies with rapid and strong flights. They have a habit of perching high at tree-top level and have also been observed to puddle on wet grounds, carrion and faeces.
Early Stages:
The early stages of the Blue Nawab have been locally observed to feed on leaves of five plants across different plant families. Of these, the Red Saga is most popularly utilized with regular sightings of caterpillars on young plants. The caterpillars feed on leaves of the host plants, and rest on the leaf upperside. The early instars rests on the midrib near the leaf tip where a silk bed has been spun. Larger caterpillars in later instars spin a silk mat across several leaves/leaflets (if the leaf or a leaflet is not large enough to accommodate the caterpillar) to create their "base camps" for rests between feeds.
Local host plant #1: Adenanthera pavonina (Red Saga).
The egg is laid singly on the upperside of a leaf/leaflet of the host plants. Each egg is yellow and spherical in shape, and its surface marked with barely distinguishable longitudinal ridges. The egg is rather large with a diameter of about 1.9mm.
The egg takes about 4 days to hatch, and the newly hatched has a body length of about 5.5-6mm. The young caterpillar eats the entire egg shell as its first meal. Its body is initially golden brown but turning green a day or two later. It has a black/brownish head with 2 pairs of curved horns, the lower of which being shorter and more straight. There is also pair of pointed process at the posterior segment.
After 5-7 days of feeding, the 1st instar caterpillar grows to a length of about 10mm. The caterpillar stays dormant in its base camp with the new head capsule growing progressively larger behind the current one. The caterpillar moults to the next instar about half a day later.
The 2nd instar has green body. Its head capsule is now reddish brown and has proportionately longer horns than those in the 1st instar, reddish brown in colour). At the other end, the posterior segment is yellowish brown and squarish, with the two anal process proportionately shorter and positioned at the two corners of this segment. After 4.5-5 days in this instar, and having the body length increased to about 15mm, the caterpillar moults again.
The head capsule of the 3rd instar caterpillar is pale beige brown initially; however all but the horns turn greenish (the horns) after a day or two. wide vertical streaks in dark brown. Some specimens might at this stage feature a small yellowish spot on the dorsum of the 3rd abdominal segment. This instar takes about 5 to 6 days to complete with body grown to about 23-26mm in length.
The head capsule of the 4th instar caterpillar is yellowish green with the horns red-tipped in most specimens. In this instar, the dorsal spot on the 3rd abdominal segment could be absent, occur as a tiny speck, a larger oval spot, and bright yellowish crescent mark (edged in black). The two anal processes are now minuscule in size and hardly distinguishable. This penultimate instar lasts a further 6-7 days with body length reaching about 34-37mm. In the last few days of the instar, pale green crescent marks start to appear on each body segment, giving us a hint of what the next instar will bring.
The 5th instar caterpillar closely resembles the 4th instar caterpillar. The horns on the head capsule are observed to be broader than those in the 4th instar, and the amount of red shading they carry varies from specimen to specimen. The same variation in the dorsal spot on the 3rd abdominal segment can be seen in this instar. Some caterpillars without the dorsal spot in the 4th instar have been observed to possess the spot in the final instar. Another noticeable change is in the posterior segment where the golden brown shading seen in in earlier instars is now absent.
The 5th instar lasts for 12-13 days typically, but might reach 16 days for some specimens. The body length could reach up to 60-65mm. Toward the end of this instar, the body gradually shortens in length. The fully grown caterpillar soon abandons its "base camp" and goes in hunt for a pupation site. Eventually the caterpillar comes to rest on a spot on the under surface of a stem. There it spins a silk pad to which it attaches its claspers (anal prolegs). The pre-pupatory larva then hangs vertically, typically with its body curled up.
Pupation takes place a day later. The pupa suspends itself from the same silk pad but now with its cremaster. The pupa has a berry like appearance with its thick and cylindrically oval shape. It is green but streaked with abundant white, especially on the leading edge of the wing pads. The tip of the pupa, where the head is sited, is colored reddish/pinky brown. Length of pupa: 24-25mm.
The pupal period lasts for about 10.5 to 11 days, and the pupa turns dark to reddish brown the night before eclosion. The white median band on the forewings also become visible through the pupal skin at this stage.
Eclosion takes place the next day. The pupal case first cracks open with the adult butterfly making its way out. It quickly turns around and perches on the underside of the pupal case to "dry" and expand its wings. A few hours later, the adult butterfly makes the first flight of its life.
References:
- [C&P4] The Butterflies of The Malay Peninsula, A.S. Corbet and H.M. Pendlebury, 4th Edition, Malayan Nature Society, 1992.
- Butterflies of Thailand, Pisuth Ek-Amnuay, 2nd Edition, 2012.
- A Field Guide to the Butterflies of Singapore, Khew S.K., Ink On Paper Communications, 2010.
