16 October 2010

Life History of the Common Banded Awl

Life History of the Common Banded Awl (Hasora chromus chromus)



Butterfly Biodata:
Genus: Hasora Moore, 1881
Species: chromus Cramer, 1780
Subspecies: chromus Cramer, 1780
Wingspan of Adult Butterfly: 45mm
Caterpillar Host Plants: Pongamia pinnata (Leguminosae).


A male Common Banded Awl perching on a leaf.


A male Common Banded Awl perching on the underside of a branch.

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. In the male, the wings are unmarked while the female has two pale yellowish crescentic spots in spaces 2 and 3 on the forewing. The male has a discal stigma on the forewing. Below, both sexes are pale purplish brown. On the hindwing, there is a prominent and narrow white to bluish white discal band partitioning the wing into an inner and an outer half. The inner edge of the band is more sharply defined compared to the outer edge. In contrast, the discal band on the forewing is faint and extends only over the upper portion of the wing. The female has two apical spots in spaces 6 and 7 of the forewing with the one in space 7 absent from some specimens.


Close-up views of the light brown and purplish scales of a female Common Banded Awl.


A male Common Banded Awl perching on the underside of a leaf.


A male Common Banded Awl perching on the underside of a grass blade.

Field Observations of Butterfly Behaviour:
This species is uncommon in Singapore. There is a better chance of finding larval stages of this species on its host plant, Pongamia pinnata, than seeing the adults up close. The fast flying adults have been observed to visit flowers for nectar. When resting, the adults typically do so on the underside of a leaf or other plant parts.


A female Common Banded Awl visiting flowers.


A female Common Banded Awl perching on a stem.

Early Stages:
The local host plant, Pongamia pinnata, is a tree which can grow up to 6-15m tall. Its compound leaf has 5-7 leaflets in a pinna. Each leaflet is thin leathery, shiny reddish brown when young, and turn darker green when matured. It is listed as "Endangered" in the latest Singapore Red Data book, and at present can be found locally in small numbers in parks and along side walks in certain built-up areas. The caterpillars of the Common Banded Awl feed on young to middle-aged leaves of this plant.


Host plant : Pongamia pinnata. Relatively young leaves are shown.

The eggs are laid singly or in small groups of 2-3 on young shoots of the host plants. Each egg is initially white and shaped like a bun with a flattened base (diameter: 0.4-0.5mm). Prominent ridges running from the pole to the base. The micropylar sits atop at the pole. The entire egg turns pinky red as it develops, and then decolorizes again when the caterpillar is ready to emerge.


Two views of a `fresh' egg of the Common Banded Awl.


Two views of a maturing egg of the Common Banded Awl.


Two views of a mature egg of the Common Banded Awl with the larval head vaguely visible.


Two views of empty egg shells of the Common Banded Awl.

It takes 2-3 days for the collected egg to hatch. The young caterpillar eats just enough of the shell to emerge, and has a length of about 2mm. It has the typical cylindrical shape for skipper caterpillars, and the yellowish brown body has a number of short 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, early in this stage, length: 1.8mm.


Two views of a 1st instar caterpillar, late in this stage, length: 2.6mm.

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 flap and ventures out to eat on nearby leaf surface. In later instars, the Common Banded Awl caterpillars also construct leaf shelters in a similar fashion but do so with larger and older leaves. The larval growth of the Common Banded Awl is rapid in pace for all five of its instars, with all but the final instar lasting only 1-1.5 days.


1st instar caterpillar, late in this stage, dormant before its moult, length: 3.2mm.

After reaching a length of about 3.2mm in the 1st instar, the caterpillar moults to the next instar after a short dormant period. The 2nd instar caterpillar has four faint whitish narrow dorsal bands and one lateral band which are barely visible against the pale yellowish body ground color. These bands become more prominent as the body ground colour turn pale brownish towards the end of this instar. The body and the head capsule are also covered in short fine setae.


Two views of a 2nd instar caterpillar, early in this stage, length: 3.3mm.


2nd instar caterpillar, late in this stage, length: 5mm.


2nd instar caterpillar, late L2, dormant before its moult, length:5.5mm.

The 2nd instar caterpillar reaches a length of about 5.5mm, and after 2 days in this stage, it moults again. The 3rd instar caterpillar resembles the 2nd instar caterpillar but with more prominent dorsal and lateral whitish bands due to the much darker brown in its ground colour. Overall the body takes on a freckled appearance with numerous tiny lighter patches dotting the dark brown surface. A narrow anal plate dark brown to black in color, can now be seen on the posterior end. This instar lasts another 1-1.5 days with the length reaching 9mm.


Two views of a 3rd instar caterpillar, early in this stage, length: 6.5mm.


Two views of a 3rd instar caterpillar, prior to its moult, length: 9mm.


The 4th instar caterpillar resembles the 3rd instar caterpillar closely, but with its body ground colour in darker brown. The whitish setae on the head capsule are proportionately much longer than in earlier instars. This stage takes about 1-1.5 days to complete with the body length reaching 19mm.


Two views of a 4th instar caterpillar, early in this stage, length: 12.3mm.


Two views of a 4th instar caterpillar, late in this stage, length: 19mm.

The final and 5th instar caterpillar has similar body markings as the 4th instar caterpillar, though the ground colour has changed to a dark shade of purplish brown or even pinky brown above the lateral band. Several large dorso-lateral spots are also present here. Below the narrow lateral band, the body is in a contrasting yellowish brown. One unmistaken change is in the head capsule which has now become pale orangy brown. Moderately long white setae are found over the whole body and the head capsule. This stage takes about 3 days to complete with body length reaching up to 36mm.


A newly moulted 5th instar caterpillar eating its `old' larval skin.


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


Two views of a 5th instar caterpillar, length: 26mm.

Towards the end of 5th instar, the body of the caterpillar gradually shrinks in length and decolorises. Some caterpillars would turn completely pale greenish whilst others retains several lateral dark spots. The fully grown caterpillar ceases feeding and stations itself in its leaf shelter and enters the preparatory pupa phase. During the early part of this stage, the caterpillar spins large quantity of 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. Both the dorsal point of the girdle and the transverse band are also secured by vertical/oblique threads to the inner wall of the shelter.


Two views of a 5th instar caterpillar, late in this stage, length:36mm.


Two views of a pre-pupa of the Common Banded Awl secured via silk girdle and anchor in its shelter.

After about 0.5-1 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 rostrum. Fresh after the pupation event, the body is greenish, but after 0.5 to 1 day, the body surface becomes mostly covered in a white substance. Length of pupae: 23-24mm.


Two views of a pupa of the Common Banded Awl with a coating of whitish powdery substance.

After 5-5.5 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.


Two views of a mature pupa of the Common Banded Awl


A newly eclosed male Common 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, 1st Edition, 2006
  • The Butterflies of Hong Kong, M. Bascombe, G. Johnston, F. Bascombe, Princeton University Pres 1999
Text by Horace Tan, Photos by Khew S K and Horace Tan

5 comments:

Blue Heron Moon said...

Another great post. Your site is one of the best for butterflies!

Thank you for taking the time to post.

Horace said...

Thanks for the kind words. :)
We are very glad that our postings have interested readers like yourself.

Khaja Nazim Abdul Hameed said...

This is the most comprehensive butterfly website in singapore.

Horace said...

Many thanks for the compliment, Khaja. :)

We are glad that we have the opportunities to share, through articles in this blog, our knowledge and photographs of butterflies in Singapore.

Rajib said...

Nice information