Butterfly Biodata:
Genus: Eulaceura Butler, 1872
Species: osteria Westwood, 1850
Subspecies: kumana Fruhstorfer, 1913
Wingspan of Adult Butterfly: 50-70mm
Caterpillar Local Host Plant: Gironniera nervosa (Ulmaceae, common name: Common Rough Laurel).
Physical Description of Adult Butterfly:
On the upperside, the male is purple brown with a prominent white discal band spanning both wings, broadening towards the tornal margin of the hindwing. The female is dull ochreous brown with obscure whitish markings on both wings. On the underside, the wings are tinged purplish blue in a side light, more so in the male. The white discal band spanning both wings are featured in both sexes, but in the female it is much thinner in the hindwing.
Field Observations of Butterfly Behaviour:
Purple Duke is common in Singapore, but its presence is restricted to the nature reserve where its host plant occur in abundance. The adults have a habit of flying rapidly in low bushes and settling on the underside of leaves. In the field, the female can be easily mistaken to be a female of Euthalia species. Both sexes have the habit of puddling and taking nectar from ripened fruits and flowers.
Early Stages:
Only one local host plant is recorded for the Purple Duke. The plant, Gironniera nervosa (Common Rough Laurel), is common in the central catchment reserve. The caterpillars of the Purple Duke feed on leaves of the host plant, with the caterpillar in all but the final instar adopting the habit of eating the leaf lamina between secondary veins.
Purple Duke can be seen on three separate leaves.
The eggs of the Purple Duke are laid singly on the leaf of the host plant, typically on the underside of the leaf. Each pale milky white egg is globular with a diameter of about 1.1mm. A number of longitudinal ridges are present. Each egg takes about 3-3.5 days to hatch. The young caterpillar nibbles away a portion of the egg shell to emerge, leaving the remnant uneaten.
With a length of about 3.5mm, the newly hatched is pale beige brown in both its body and head. There are a number of narrow whitish bands running length-wise on the body surface. The caterpillar also features two backward-pointing black-tipped anal processes.
As the 1st instar caterpillar grows up to a length of about 7-7.5mm, the body takes on a strong green undertone. After about 2.5-3 days in the 1st instar, the caterpillar moults to the next instar.
The 2nd instar caterpillar has a few changes in its appearance as compared to the 1st instar caterpillar. Now the body ground colour is green, and the longitudinal bands are whitish to yellowish. The head capsule is black with two large cephalic horns, featuring side branches on the lateral peripherals as well as on the cephalic horns. This instar lasts about 4-5 days with the body length reaching up to 11mm before the next moult.
The 3rd instar caterpillar resembles the 2nd instar caterpillar closely. The main change occurs in the head capsule where the black lateral processes and cephalic horns are proportionately longer. The head is mostly pale brownish. The many longitudinal bands in the earlier instar give way to a checkerboard pattern of yellow and green. The 3rd instar takes about 4-5 days to complete with the body length reaching up to 16-17mm.
The 4th instar caterpillar resembles the 3rd instar caterpillar with the main change occurring again in the head capsule. Now the "face" is whitish green and the body appears to be predominantly green and adorned with numerous tiny yellowish spots. It has two prominent, pale whitish to yellowish dorso-lateral bands. This penultimate instar lasts about 7 to 10 days with body length reaching about 26-27mm.
The next moult brings the caterpillar to its 5th and final instar. Now the head capsule is mostly whitish green and the cephalic horns pale reddish brown. The two pointed anal processes are greenish to pale reddish brown in colour.
The 5th instar lasts about 11-13 days, and the body length reaches up to 45-47mm. In this instar, the caterpillar does not avoid secondary veins of the leaf when feeding.
Toward the end of the 5th instar, the body gradually shortens in length with the body base colour turning to translucent green. Eventually the caterpillar comes to rest on a chosen spot on the underside of a leaf. Here it stays dormant for a while before spinning a silk pad and anchoring its anal claspers to it. It then becomes an pre-pupatory larva in this upside-down pose.
Pupation takes place about 0.5-1 day later. The pupa suspends itself with a cremastral attachment to the silk pad on the substrate. The pupa is mainly green mottled with cryptic yellowish markings. Each pupa has a pair of short cephalic horns. The body has a slight keeled appearance as it broadens and tapers to a yellowish ridge on the dorsum. Length of pupae: 24-26mm.
After 6 days of development, the pupa turns yellowish brown in the abdomen and black in the wing pads as the development within the pupal case comes to an end. The next day the adult butterfly emerges from the pupal case.
A female Purple Duke emerges from its pupal case.
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, 2nd Edition, 2015.
