16 April 2011

Life History of the Horsfield's Baron

Life History of the Horsfield's Baron (Tanaecia iapis puseda)

Butterfly Biodata:
Genus: Tanaecia Butler, 1869
Species: iapis
Godart, 1824
Subspecies: puseda Moore, 1858
Wingspan of Adult Butterfly: 65mm
Caterpillar Host Plants:
Melastoma malabathricum (Melastomataceae).

A female Horsfield's Baron giving us a view of its upperside.

A male Horsfield's Baron displaying its wing upperside.

Physical Description of Adult Butterfly:

T. iapis puseda exhibits sexual dimorphism. Above, the male is dark velvety black with its hindwing hosting a broad greenish-blue distal border which is continued narrowly along the termen of the forewing. The larger female is pale ochreous brown, and has a post-discal series of helmet-shaped white spots and a less distinct marginal series of spotts on both fore- and hindwings. Underneath, the male is pale ochreous brown with a series of dark striae in the forewing cell, but without any white spots. The female has additional marginal and post-discal series of whitish spots on both fore- and hindwings.

A puddling male Horsfield's Baron.

A male Horsfield's Baron perching with a closed-wing posture.
Field Observations of Butterfly Behaviour:
The Horsfield's Baron is relatively common in Singapore. They are mainly found in the nature reserves, but at times adults can be seen flying in public parks and wastelands where the host plants are growing in abundance. Both sexes have the habit of resting on perches with wings open. The male exhibits territorial behaviour of chasing intruders in the vicinity of its perch. On rare occasions, the male have been observed to puddle on damp ground. Refer to this earlier butterfly-of-the-month article for a more detailed write-up on this species.

Early Stages:
The host plant, Melastoma malabathricum, is a widespread weed in Singapore. An earlier blog article has a detailed write-up of its characteristics and its relationship with other local butterfly species. Caterpillars of Horsfield's Baron feed on the middle-aged to mature leaves of this amazing plant.

Host plant : Melastoma malabathricum. Leaves, flower buds and flowers are shown.

A mating pair of the Horsfield's Baron.

A mother Horsfield's Baron laying an egg at a leaf tip of the host plant.

The eggs are laid singly at the leaf tip of the host plant. Each egg has a tall dome shape with a base diameter of about 1.8mm. 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 Horsfield's Baron.

Two views of a near-mature egg of the Horsfield's Baron, one day prior to hatching.

After about 4.5-5 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 and "fleshy" dorso-lateral protuberances. Black setae emanate from the body below these long protuberances and from a series of short dorsal protuberances. Frass pellets are usually seen attached to the tip of these setae in this instar. The caterpillar grows from an initial length of about 4mm to 6mm in 1.5-2 days. The subsequent moult takes it to the 2nd instar.

Two views of a newly hatched 1st instar caterpillar. Top: taking a pause after emergence; Bottom: nearly done with eating its own egg shell.
Two views of a 1st instar caterpillar, early in this stage, length: 4mm.

1st instar caterpillar, late in this stage, dormant prior to the moult, length: 5.5mm

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 with some spines colored black in the middle and the tip portion. On the dorsum, pairs of white patches appear between the 3rd to the 10th protuberances. As growth progresses in this instar, each pair of white patches become conjoined to appear as an eye-shaped patch. The 2nd instar lasts for 3-4 days with the body length reaching about 9.5-10mm 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.

Two views of 2nd instar caterpillar, early in this stage, length: 8mm

A 2nd instar caterpillar, length: 8.5mm

A 2nd instar caterpillar, late in this stage, dormant prior to its moult, length: 8mm.

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. Dorsally the series of eight white-oultined patches become more prominent, and toward the later part of this instar, the central portion of each patch becomes darkened. The 3rd instar lasts for 3.5-4 days and reaches a length of about 15-16mm before the next moult. Towards the end of this instar, the body color gradually changes to jade green.

A newly moulted 3rd instar caterpillar. Note the exuvia lying nearby.

Two views of a 3rd instar caterpillar, length: 11mm.

3rd instar caterpillar, late in this stage, length: 15mm

The 4th instar caterpillar has similar appearance as in the 3rd instar but with a pale yellowish green body color. 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 white. The dorsal marks becomes more shield-like in appearance with the central portion taken up by a large purplish/pinkish patch encircling a small dark bluish spot. After 5-6 days in this instar, with its length reaching 22-24mm, the caterpillar moults to the 5th and final instar.

A 4th instar caterpillar which has just shed its old skin.

Dorsal view of a 4th instar caterpillar, length: 22mm.

Another view of the 4th instar caterpillar.

Essentially similar to the 4th instar caterpillar, the 5th instar features a darker shade of jade green. The number of small white spots on the body has increased. The dorsal shield-like spots are also larger and more prominent visually.

5th instar caterpillar, early in this stage, length: 25mm.

5th instar caterpillar, first 2 dorsal spots.
5th instar caterpillar, last 3 dorsal markings.
5th instar caterpillar, late in this stage, length: 35mm.
This final instar lasts for 7-9 days with the caterpillar reaching a mature length of about 35-38mm. On the last day, the caterpillar ceases its feeding activity and its body becomes shortened. It then seeks out a spot on the underside of a mature leaf and stays put. There it laboriously 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, each dorsal shield-like markings has decolorized to become just a ring of white surrounding a central green to dark blue patch. A short transverse white band appears on the dorsum about mid-body. Nearing the end of the pre-pupal phase, all traces of dorsal markings are nearly gone except for the very first one which becomes a yellow spot. The short transverse band turns yellow by this time too.

Two views of a pre-pupa of the Horsfield's Baron. Left: early pre-pupa; Right: late pre-pupa.

After 0.75-1 day of the pre-pupal stage, pupation takes place. The 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 high transverse dorsal ridge which is lined with an interrupted golden transverse band. The green pupa has a series of golden-colored spots symmetrically arranged. Two short golden-colored cephalic horns are also featured. Length of pupae: 18-20mm.

The pupation event of a Horsfield's Baron caterpillar.

Two views of a newly formed pupa of the Horsfield's Baron.

Two views of a pupa of the Horsfield's Baron.

Nine 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 ecloses and stays near the empty pupal case for an hour or two before taking its first flight.

Two views of a mature pupa of the Horsfield's Baron.

A newly eclosed male Horsfield's Baron clinging on its empty pupal case.

A newly eclosed male Horsfield's Baron.

  • [C&P4] The Butterflies of The Malay Peninsula, A.S. Corbet and H.M. Pendlebury, 4th Edition, Malayan Nature Society.
  • Butterflies of Thailand, Pisuth Ek-Amnuay, 1st Edition, 2006
Text by Horace Tan, Photos by James Chia, Ellen Tan, Sunny Chir, Khew SK and Horace Tan

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