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he commoner of the two known species
of the genus Polyura 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. The underside has a large, pale silvery green median patch, which
covers a little more than a quarter of the wing.
Polyura hebe is represented by the race plautus in
Singapore, and is characterized 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 in the female and narrower and sharper in
the male.
The butterfly has a strong and erratic flight, and is difficult to
capture on the wing. It has a habit of perching on a lofty leaf or
branch, surveying the grounds below. It then flies rapidly in the
vicinity, often coming back again and again to the same preferred perch
to rest. We have found this species feeding on roadside seepages,
carrion, faeces and tree sap.
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Adenanthera pavonina |
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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, which appears to be an alternative host plant.
The young caterpillar is bright green, taking the colour of the green Saga
leaves, onto which it very effectively merges as it camouflages itself. The
four-horned head is black in the early instars. 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.
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Interestingly, the species has a rather high
mortality rate as it falls prey to parasitic flies and wasps. We have often
found the pupa case with a small round hole in it, indicating that the
caterpillar has been parasited before it pupated, and all that emerged from
the pupa were the flies or wasps that used the caterpillar as its host.
The four-horned head of this species gives
it an almost ‘dragon-like’ appearance and it is a rather interesting looking
caterpillar. The caterpillar stage of the Plain Nawab lasts about 2 weeks,
during which it feeds voraciously. At the last instar, it curls its body
into a ball, finally pupating into a berry-like pupa, complete with
green-striped variegations to help camouflage itself.
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