17 January 2015

Life History of the Small Branded Swift

Life History of the Small Branded Swift (Pelopidas mathias mathias)


Butterfly Biodata:
Genus: Pelopidas Walker, 1870
Species: mathias Fabricius, 1798
Sub-Species: mathias Fabricius, 1798
Wingspan of Adult Butterfly: 32-36mm
Caterpillar Local Host Plant: Axonopus compressus (Poaceae, common names: Wide-leaved Carpet Grass, Cow Grass).


A male Small Branded Swift giving a view of the upperside of its forewing.

A close-up view of the forewing upperside, illustrating post-discal spots in spaces 2-4, 6-8, two cell spots and the brand.

Physical Description of Adult Butterfly:
On the upperside, the wings are brown, greenish at the base. There are white post-discal hyaline spots in spaces 2-4, 6-8 and two cell spots in the forewing. The male has a narrow oblique brand in the forewing running from the spot in space 2 towards the dorsum (the brand is angled in such a way that a line drawn from and through the two cell spots would intersect it). The female has additional white spots in spaces 1b, consisting of one minute upper spot and one larger lower spot. On the underside, the wings are pale brown with a greyish tone. The forewing has the same spots as per the upperside, and the hindwing has a cell spot and post-discal spots in space 2 to 5.

The upperside view of a female Small Branded Swift, showing the two additional post-discal spots in space 1b.

A female Small Branded Swift observed at the forest edge in the nature reserve.

The same female Small Branded Swift in the above picture partially opens its wing to sun-bathe.

Field Observations of Butterfly Behaviour:
The Small Branded Swift is common in Singapore. The adults have been sighted in multiple locations including nature reserves, wastelands, urban parks and gardens across the island. The adults fly with a swift, strong and darting flight. They have been observed to sunbathe with open wings in sunny condition, visiting flowers and puddling on wet grounds.




Early Stages:
The Small Branded Swift has so far been bred on just one grass species locally, Axonopus compressus (Cow Grass), a very common grass species carpeting the ground across the island. The caterpillars feed on leaves of the host plant, and live in shelters formed by joining edges of a grass blade together.

Local host plant: Axonopus compressus.

A mating pair of the Small Branded Swift.

The eggs are laid singly on the upperside of a grass blade of the host plant. Each dome-shaped egg is whitish with a basal diameter of about 1mm and a height of about 0.75mm. The micropylar sits atop and a number of very fine and obscure ridges running longitudinally from it.

Two views of an egg of the Small Branded Swift.

Two views of a maturing egg, with the black head capsule visible through the egg shell.

It takes about 3.5-4 days for the egg to hatch. The young caterpillar eats just enough of the shell to emerge, and has a length of about 2-2.2mm. Its cylindrical body is whitish with a yellowish tone, and a tuff of few moderately long setae can be found at the posterior end. The head capsule is black and right behind it a black collar mark is present on the prothorax. The newly hatched nibbles away most of the egg shell remnant before proceeding to construct its first leaf shelter.

The newly hatched caterpillar eating its own egg shell.

Two views of a newly hatched caterpillar, length: 2.2mm.

A newly hatched caterpillar in its very first leaf shelter. Further "stitching" work by the caterpillar will bring the two opposite edges together.

The body turns yellowish green after the caterpillar has a few sessions of the leaf diet. By the time the caterpillar lies dormant for its moult to the 2nd instar, its length has reached 3.8-4mm. The 1st instar takes a total of 3 days to complete.

Two views of a 1st instar caterpillar, length:3.2mm.

The 2nd instar caterpillar still has a yellowish green body, and the head capsule is still black. The black collar mark on the prothorax has faded to just to hint of its presence. Faint whitish doro-lateral and lateral bands are observable. This instar lasts about 3 days with the body length reaching about 6mm.

Two views of a 2nd instar caterpillar, early in this stage, length: 4.6mm.

Two views of a 2nd instar caterpillar, late in this stage, length: 5.9mm.

The 3rd instar caterpillar still has a black head capsule but the dorso-lateral and lateral bands are now more prominent, whitish to yellowish in coloration. There is no longer any trace of the black collar mark on the prothorax. This instar lasts about 3 days with the body length reaching about 10-11mm.

Two views of a 3rd instar caterpillar, early in this stage, length: 5.9mm.

A 3rd instar caterpillar, late in this stage, length: 10mm.

The 4th instar caterpillar has a head capsule which is whitish in ground colour but dark brown to black along the periphery and various sulci. Two dark and broad stripes rise from the adfrontal area. This penultimate instar lasts about 3 days with the body length reaching up to 17-18mm.

Two views of a 4th instar caterpillar, early in this stage, length: 10.4mm.

Two views of a 4th instar caterpillar, late in this stage, length: 16.2mm.

The 5th instar caterpillar features a different head capsule which is pale green in ground colour. The periphery is marked with a broad band. The colour of the band varies from red, dark red to black. The peripheral bands are flanked with narrower whitish on both the inner and outer sides. The anal plate is unmarked as in the all previous instars. This final instar takes about 5 days to complete with the body length reaching 33-35mm.

Two views of a 5th instar caterpillar, early in this stage, length: 16.8mm.

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

Three 5th instar caterpillars, male, showing variations in the color of the peripheral bands on the head capsules.

Towards the end of 5th instar, the body of the caterpillar shortens in length and body colour assumes a uniform shade of pale lime green. It seeks out a spot on a leaf blade where it constructs a shallow but half-open shelter with silk threads at both ends. The body excretes a moderate amount of white waxy material at this stage. Within the shelter, a silk girdle and a silk pad are then spun. Once the caterpillar attaches its claspers to the silk pad, it enters the dormant prepupatory phase which lasts about one day.

Two views of a dormant pre-pupa of The Small Branded Swift.

The pupa secures itself with the silk girdle and with its cremaster attached to the silk pad. It has a short thorax, a rather long abdomen and a pointed rostrum. The body is deep lime green in the thorax and wing case but yellowish green in the abdomen. Narrow, whitish, dorso-lateral and lateral bands run lengthwise on the abdomen. Length of pupae: 24-25mm.

Two views of a pupa of the Small Branded Swift.

After 7 days, the pupa becomes mostly black in color in the wing pads and in the body segments. Eclosion takes place the next day.

Two views of a mature pupa of the Small Branded Swift.

A newly eclosed Small Branded Swift.

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 Bendecit Tay, PF Loke and Horace Tan

1 comment:

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