Life History of the Malay Baron

Life History of the Malay Baron (Euthalia monina monina)

Butterfly Biodata:
Genus: Euthalia Hübner, 1819
Species: monina Fabricius, 1787
Subspecies: monina Fabricius, 1787
Wingspan of Adult Butterfly: 50-70mm
Local Caterpillar Host Plants: Macaranga bancana (Sapotaceae, common name: Common Mahang), Bhesa paniculata (Celastraceae, common name: Malayan Spindle Tree).

A male Malay Baron, -f. decorata.

A male Malay Baron, -f. decorata.

A male Malay Baron, -f. monina.

Physical Description of Adult Butterfly:

The Malay Baron exhibits sexual dimorphism. On the upperside, the male is dark brown. In the typical form -f. monina, the distal border on the hindwing is blue and bears a series of small black sagittate markings. In form -f. decorata, the upperside is paler brown with more clearly defined post-discal fasciae and the hindwing has a coppery green border. In form -f. gardineri, the upperside is dark brown with obscure fasciae and the hindwing border is not additionally coloured. At times, males could appear bearing appearances integrating the above 3 forms. The female resembles the female Tanaecia iapis (Horsfield's Baron) with the exception of the presence of a dark zigzagged line in the white post-discal band on the forewing.

A female Malay Baron.

A male Malay Baron, -f. monina.

Field Observations of Butterfly Behaviour:

The Malay Baron is common in Singapore. They are mainly found in the nature reserves, but at times adults can be seen flying in public parks and gardens. Both sexes have the habit of visiting flowers or ripened fruits for nectar and feeding on fallen fruits on forest floor.

A male Malay Baron, -f. gardineri.

Early Stages:

Both host plants, Macaranga bancana and Bhasa paniculata, are common in the nature reserves, with the former being the more commonly utilized host plant. Caterpillars of Malay Baron feed on the mature leaves of both host plants, and rest on the leaf upperside between feeds.

Local host plant #1 : Macaranga bancana (Common Mahang).

Local host plant #2 : Bhesa paniculata (Malayan Spindle Tree).

Left: A mother Malay Baron ovipositing on a leaf of Macaranga bancana; Right: the egg deposited.

A mother Malay Baron laying an egg on a leaf of Bhasa paniculata.

The eggs are laid singly on the leaf upperside of the host plant. Each egg has a tall dome shape with a base diameter of about 1.9-2.0mm. The surface is covered with large hexagonal depressions with hair-like protuberances emerging from adjoining corners. When freshly laid, the surface is moist and in pale green. Within hours, the moisture evaporates and the color turns to a darker shade of green.

Two views of an egg of the Malay Baron.

Two views of a mature egg of the Malay Baron.

After about 5 days, the 1st instar caterpillar emerges and proceeds to eat the eggshell as its first meal. The caterpillar is yellowish green in body colour and has a pale yellowish brown head capsule adorned with two brownish lateral stripes. Its body sports ten pairs of long, whitish and "fleshy" dorso-lateral protuberances. Black setae emanate from the body below these long protuberances and from a series of short dorsal protuberances. The caterpillar grows from an initial length of about 3.9mm to 6mm in about 3 days.

Two views of a 1st instar caterpillar, early in this stage, length: 3.9mm.

Two views of a 1st instar caterpillar, length: 5mm.

1st instar caterpillar, late in this stage, dormant prior to the moult, length: 5.8mm

The body of the 2nd instar caterpillar is predominantly yellowish green. All ten pairs of short protuberances seen in the 1st instar have lengthened considerably. Each is projected horizontally with numerous branched spines and is almost always pressed to the leaf surface. The protuberance is mainly pale yellowish in color. On the dorsum, white patches appear between the 3rd to the 10th protuberances. As growth progresses in this instar, each white patch become better defined and take on oblong to ellipse shape. The 2nd instar lasts for 3 days with the body length reaching about 10mm before the moult to the 3rd instar. Note that the length given here and for later instars is measured between the head and the posterior end of the last body segment, excluding the length of protuberances projected head and behind the body segments.

A 2nd instar caterpillar, early in this stage, length: 5.2mm

Two views of a 2nd instar caterpillar, length: 9.7mm

A late 2nd instar caterpillar, dormant prior to its moult.

The 3rd instar caterpillar is still greenish in body color. There are a few small spots on the body. The protuberances have all become much longer in proportion. The branched spines appear almost like a bird's feather, with the secondary spines arranged neatly around the main spine. Some of the branched spines are black. Dorsally the series of eight white patches become longer and more prominent. The 3rd instar lasts for about 3 days and reaches a length of about 13-14mm before the next moult.

A newly moulted 3rd instar caterpillar. Note the head capsule nearby.

Two views of a 3rd instar caterpillar, length: 12mm.

A late 3rd instar caterpillar, dormant prior to its moult, length: 12mm

The 4th instar caterpillar has similar appearance as in the 3rd instar. Horizontal spines on each long protuberance are mostly pale green while shorter vertical spines are black in color. The distal portion of the protuberance is mostly colored black with white tips. The dorsal marks are longer and almost touching each other. After about 3-4 days in this instar, and its body length reaching 22-23mm, the caterpillar moults to the 5th instar.

A newly moulted 4th instar caterpillar.

Two views of a 4th instar caterpillar, length: 17mm.

A late 4th instar caterpillar, dormant prior to its moult, length: 21mm.

The 5th instar caterpillar features a darker shade of jade green and all dorsal patches are fused together to form a continuous yellowish band. Faint pinkish patches are seen embedded in this band. After about 3-4 days in this instar, with its length reaching 28mm, the caterpillar moults to the 6th and final instar.

A newly moulted 5th instar caterpillar, length: 18.5mmmm.

Two views of a 5th instar caterpillar, length: 28mmmm.

A late 5th instar caterpillar, dormant prior to its moult, length: 28mm.

The 6th instar caterpillar resembles the 5th instar caterpillar closely. In some specimens, the pinkish marks embedded in the dorsal band are more prominent and distinct. The caterpillar has the tendency of resting on the upperside of the leaf with its yellowish dorsal band aligned with the similarly coloured main/secondary vein, allowing it to blend in the surrounding.

A newly moulted 6th instar caterpillar of the Malay Baron.

Two views of a 6th instar caterpillar, length: 34mm.

A late instar caterpillar observed in the field on a leaf of Macaranga bancana.

This final instar lasts about 9 days with the caterpillar reaching a mature length of about 40mm. On the last day, the caterpillar ceases its feeding activity and its body shrinks in length. It then seeks out a spot on the underside of a mature leaf and stays put. There it spins large quantity of silk threads to make a silk mound, to which its posterior claspers are then attached to. Now the pre-pupa hangs from this anchor point in a head-down posture. By this time, the dorsal band has whitened entirely. Later, a short transverse white band appears on the dorsum about mid-body with a pinkish mark embedded.

Two views of a pre-pupa of the Malay Baron, early in this stage.

A pre-pupa of the Malay Baron, late in this stage, showing the transverse band.

After about 1 day of the pre-pupal stage, pupation takes place. The green pupa is suspended with its cremaster firmly attached to the silk mound. It has a smooth body which tapers steeply towards each end from a reddish transverse dorsal ridge which is lined with a number silvery spots. The dorsal ridge is marked in red from this transverse band to mid-thorax where it ends in a large silvery spot. Two short silvery cephalic horns are also featured. Length of pupae: 21-22mm.

Two views of a pupa of the Malay Baron.

Eight days later, the pupa becomes considerably darkened, especially in the wing case area, signaling the end of the development of the adult still encased within. The next day, the adult butterfly emerges.

Two views of a mature pupa of the Malay Baron.

A newly eclosed male Malay Baron clinging on its empty 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, 2010.

Text by Horace Tan, Photos by Mark Wong, Loke PF, Frederick Ho, Sunny Chir, Khew SK and Horace Tan