Life History of the Plain Banded Awl

Life History of the Plain Banded Awl (Hasora vitta vitta)

Butterfly Biodata:
Genus: Hasora Moore, 1881
Species: vitta Butler, 1870
Subspecies: vitta Butler, 1870
Wingspan of Adult Butterfly: 40-45mm
Caterpillar Local Host Plant: Spatholobus ferrugineus (Family: Fabaceae)

A Plain Banded Awl perching on the underside of a leaf.

A Plain Banded Awl visiting a flower of the Singapore Rhododendron.

A Plain Banded Awl taking nectar from an Ixora flower.

Physical Description of Adult Butterfly:

Adults are rather large in size with pointed forewing apex and markedly lobate hindwings. Above, the wings are dark brown. Both sexes have one small hyaline subapical spot in the forewing, with the female having two larger hyaline spots in spaces 2 and 3 in addition. There are no cell spots, and the male does not have a discal stigma on the forewing. Below, both sexes are pale brown with a purplish sheen in fresh specimens. The hindwing has a prominent white and outwardly diffuse discal band. The inner half of the hindwing has a greenish glaze, more so in the male than in the female.

Field Observations of Butterfly Behaviour:

This species is moderately rare in Singapore. The adults have been sighted in both nature reserves and urban parks and gardens, typically during the dawn and dusk hours of a day. They have the habit of visiting flowering plants for nectar and puddling on damp patches for minerals. As with other Awl spp., the fast flying adults have a habit of resting on the underside of a leaf or other plant parts.

A Plain Banded Awl puddling on a damp ground.

Another puddling Plain Banded Awl.

Early Stages:

The only recorded local host plant for the Plain Banded Awl is Spatholobus ferrugineus, a widely distributed vine in the nature reserves. This plant is tri-foliated with leaves and stems covered in a dense coat of hair. Elsewhere in the region (Malaysia, Thailand, Hong Kong), Milletia spp. have been recorded as alternative host plants. It is likely that at least one local Milletia spp. is a larval host too. Caterpillars of the Plain Banded Awl feed on young leaves of the host plant, and lives in leaf shelters constructed by folding cut leaf fragments.

Local host plant: Spatholobus ferrugineus.

A female Plain Banded Awl ovipositing on the young shoot of S. ferrugineus.

Eggs of the Plain Banded Awl. Left: Laid on a young leaf bud; Right: Laid on a stem.

The eggs are laid singly on young shoots of the host plants, either on a leaf bud or on the stem. Each egg is shaped like a bun with a flattened base (diameter: 0.8-0.9mm). Longitudinal ridges run from the pole to the base. The micropylar sits atop at the pole. Initially creamy white when freshly laid, the entire egg turns salmon red as it develops, and then decolorizes again when the caterpillar is ready to emerge.

Two views of an egg of the Plain Banded Awl, the day after it was laid.

Two views of a mature egg of the Plain Banded Awl, with the black head capsule showing through the hole in the egg shell.

It takes 3-4 days for the egg to hatch. The young caterpillar eats just enough of the shell to emerge, and has a length of about 1.8-1.9mm. The newly hatched does not bother to devour the rest of egg shell. It has the typical cylindrical shape for skipper caterpillars, and the yellowish brown body has a number of short white setae. The large head is black, slightly bi-lobed and lightly hairy. The dorsum of the prothorax carries a dark-colored patch/shield.

Two views of a 1st instar caterpillar, newly hatched, length: 1.9mm.

Two views of 1st instar caterpillar, length: 3mm.

The young caterpillar constructs its first leaf shelter by bringing two halves of a small young leaf together with silk threads. It rests within the shelter between feeds on nearby leaf lamina. In later instars, the Plain Banded Awl caterpillars also construct leaf shelters in a similar fashion but do so with larger and more developed leaves. As the caterpillar feeds and grows, the body base colour becomes paler and brown ring markings on body segments appear and darken towards the end of the instar.

Two views of a 1st instar caterpillar, late in this stage, dormant before its moult, length: 4mm.

After reaching a length of about 4mm in the 1st instar, the caterpillar moults to the next instar. The 2nd instar caterpillar has a pale yellowish ground colour with dark brown rings on the body segments (2 rings to each segment). Four yellowish/whitish narrow dorsal bands cut across the the dark rings. The body and the black head capsule are covered in short fine setae.

Two views of a newly moulted 2nd instar caterpillar.

Two views of a 2nd instar caterpillar, length: 5.8mm.

Two views of a 2nd instar caterpillar, dormant prior to its moult, length: 7mm.

An early 2nd instar caterpillar seen in a partially open leaf shelter.

The 2nd instar caterpillar reaches a length of about 7mm, and after about 2 days in this stage, it moults again. The 3rd instar caterpillar resembles the 2nd instar caterpillar but with somewhat broader and more prominent dark rings on the body segments. This instar lasts another 2 days with the length reaching 11mm.

Two views of a 3rd instar caterpillar, newly moulted, length: 7mm.

Two views of a 3rd instar caterpillar, late in this stage, length: 11mm.

The 4th instar caterpillar resembles the 3rd instar caterpillar initially, but with dorsal bands and segmental rings much more constrasting. The head capsule is still black for most 4th instar caterpillars, but some specimens have been observed to feature small lateral patches of red to reddish brown. This penultimate instar takes about 3 days to complete with the body length reaching up to 22mm. As the caterpillar grows in this instar, the dark segmental rings lose their prominence and decolorise in most segments (except for the prothoracic segment, 2nd and 4th abdominal segments). At the same time, the body base colour takes on a greater emphasis of yellow.

Two views of a 4th instar caterpillar, newly moulted, length: 11mm.

Two views of a 4th instar caterpillar, length: 22mm.

A 4th instar caterpillar, dormant before the next moult, length: 20mm.

The final and 5th instar caterpillar is predominantly yellow with black lateral patches on the prothoracic, 2nd and 4th abdominal segments. A much more striking change is in the head capsule which has now become reddish or orangy red. Set against this brightly coloured background are two lateral-frontal round black spots, two lateral round black spots encasing the eyes, and and one triangular black spot on the frons (about the labrum). White setae adorn the head capsule as well as the entire body. This stage takes about 6-7 days to complete with body length reaching 36-38mm.

Two views of a newly moulted 5th instar caterpillar, early in this stage, length: 19mm.

Two views of a 5th instar caterpillar, late in this stage, length: 38mm.

Towards the end of 5th instar, the body of the caterpillar gradually shrinks in length and changes colour to pale orangy brown with a reddish tone. The fully grown caterpillar ceases feeding and stations itself in its leaf shelter. During the early part of this pre-pupal stage, the caterpillar spins multiple silk threads to seal the pupation shelter, and in particular, constructs a silk girdle at its 2nd/3rd abdominal segment and a short transverse silk band near its posterior end.

Two views of a pre-pupa of the Plain Banded Awl secured in its pupal shelter.

After about 0.75 day of the pre-pupal phase, pupation takes place within the pupation shelter. The pupa secures itself with its cremaster attached to the transverse band. The pupa has a short thorax, a rather long abdomen and a short and pointed black rostrum. Fresh after the pupation event, the body is pale orangy brown overall. After 0.5 to 1 day, the body surface becomes mostly covered in a white substance. Several black spots adorn the dorsum of the thoracic segments. The spiracles are marked in black. Length of pupae: 23-24mm.

Two views of a pupa of the Plain Banded Awl, day 2 in this stage, now with the coating of whitish powdery substance.

After 8 days, the pupa becomes darkened in color signaling the imminent emergence of the adult. The next day the adult butterfly emerges from the mature pupa.

Three views of a maturing/mature pupa of the Plain Banded Awl, within the last 12 hours of the pupal stage.

A newly eclosed Plain Banded Awl.

References:

• The Butterflies of The Malay Peninsula, A.S. Corbet and H.M. Pendlebury, 4th Edition, The Malayan Nature Society.
• Butterflies of Thailand, Pisuth Ek-Amnuay, 2nd Edition, 2012

Text by Horace Tan, Photos by Bobby Mun, Loke PF, Nelson Ong, Simon Sng, Federick Ho, Sunny Chir, Khew SK and Horace Tan