16 May 2008

Butterfly of the Month - May 2008

The Plain Nawab (Polyura hebe plautus)

The Plain Nawab (Polyura hebe plautus) belongs to the sub-family Charaxinae, which feature large, heavy-bodied robust butterflies which are capable of rapid and swift flight. There are seven known species of this genus in Malaysia, of which two are found in Singapore. Both species, the Plain Nawab (Polyura hebe plautus) and the Blue Nawab (Polyura schreiber tisamenus) are not considered very rare.

The Plain Nawab is the commoner of the two known species of the genus in Singapore. The butterfly is greenish white above and the forewing has a broad black apical border, which is very wide at the apex, but decreases in width towards the tornus and base of the costa. There is a greenish white subapical spot on the forewings and a series of submarginal spots on the hindwings.

The underside has a large, pale silvery green median patch, which covers a little more than a quarter of the wing. It is represented by the subspecies plautus in Singapore, and which can be distinguished by a broad black bordered hindwing. The Malaysian subspecies that is usually encountered, chersonesus, has a narrow hindwing border.

As in most of the typical Polyura species, the hindwings of the Plain Nawab feature a pair of short stubby tails each – slightly broader and longer in the female and narrower and sharper in the male.The butterfly has a strong and erratic flight. It has a habit of perching on a lofty leaf or branch, surveying the grounds below. It then flies rapidly in the vicinity of its perch, often 'attacking' intruders and chasing other flying objects away, but coming back again and again to the same preferred perch to rest. This species can also be observed puddling on roadside seepages, carrion, faeces and tree sap.

A Plain Nawab puddling at a sandy seepage.

A Plain Nawab feeding on tree sap

The caterpillar of the Plain Nawab feeds on the Leguminosae Adenanthera pavonina (commonly known as the Red Saga). Females of this species have also been observed ovipositing on the young Petai (Parkia speciosa) plant, and Albizzia (Falcataria moluccana) both of which appear to be an alternative host plants.

Its habit of weaving a silken pad on one of the leaves as its “base camp”, from which it makes it nocturnal forays to other parts of the Saga plant to eat, is a behaviour unique to both the Polyura species in Singapore. As the caterpillar grows larger, it takes on a two-shade green appearance, with triangular wedge-shaped stripes along the length of its body. It is interesting that it still maintains its silken pad base-camp, although the pad now consists of many leaves weaved together to accommodate the large caterpillar. It makes no attempt to conceal itself, and stays stationary on its silken pad in the daytime, feeding mostly at night.

Final instar caterpillar of the Plain Nawab resting on its "base camp". The host plant is Falcataria moluccana  in this case.

Another puddling Plain Nawab

Mating pair of the Plain Nawab

Text by Khew SK : Photos by Horace Tan, James Chia and Khew SK

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