09 April 2016

Life History of the Conjoined Swift

Life History of the Conjoined Swift (Pelopidas conjunctus conjunctus)


Butterfly Biodata:
Genus: Pelopidas Walker, 1870
Species: conjunctus Herrich-Schäffer, 1869
Sub-Species: conjunctus Herrich-Schäffer, 1869
Wingspan of Adult Butterfly: 42-45mm
Caterpillar Local Host Plant: Panicum maximum (Poaceae, common names: Guniea Grass).




Physical Description of Adult Butterfly:
On the upperside, the wings are dark brown. There are pale yellowish-white hyaline spots in spaces 2-4, 6-8 and two cell spots in the forewing. Both sexes also have an additional spot in space 1b of the forewing. On the underside, the wings are paler ochreous brown. The forewing has the same spots as per the upperside, and the hindwing has a cell spot and a series of post-discal spots in spaces 2 to 5.



Field Observations of Butterfly Behaviour:
The Conjoined Swift is moderately rare in Singapore. Unrecorded and likely missed by early butterfly researchers, it was discovered recently and added to the Singapore checklist. The adults have been sighted at grassy wastelands and fringes of nature reserves. They fly with a swift, strong and darting flight.




Early Stages:
The Conjoined Swift has so far been bred on one grass species locally, Panicum maximum, a common grass species in grassy wastelands. Elsewhere, the Conjoined Swift's recorded host plants include Sugar Cane (Saccharum officinarum), Corn (Zea mays), Rice (Oryza sativa), Andropogon and Bambusa spp. The caterpillars feed on leaves of the host plant, and live in shelters formed by joining edges of the grass blade together.

Local host plant: Panicum maximum.

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 1.4mm.

Two views of an egg of the Conjoined Swift.

A mature egg of the Conjoined Swift, with the head capsule visible through hole in the egg shell.

It takes about 4 days for the egg to hatch. The young caterpillar eats just enough of the shell to emerge, and has a length of about 3.2mm. Its cylindrical body is pale cream-yellow with a tuff of moderately long setae at the posterior end. The head capsule is black and has a black collar mark 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 in its first leaf shelter.

The body turns yellowish green after the caterpillar starts feeding on the grass blade near its shelter. By the time the caterpillar lies dormant for its moult to the 2nd instar, its length has reached 5.5-6mm. The 1st instar takes about 4 days to complete.

Two views of a 1st instar caterpillar of the Conjoined Swift, length:5.5mm.

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 away almost completely. Faint whitish doro-lateral and lateral bands are observable. This instar lasts about 4-5 days with the body length reaching about 8-9mm.

Two views of a 2nd instar caterpillar, early in this stage, length: 5.5mm.

Two views of a 2nd instar caterpillar, length: 7mm.

The 3rd instar caterpillar resembles the 2nd instar caterpillar closely, except for the larger head and body size. This instar lasts about 3 days with the body length reaching about 12.5-13mm.

Two views of a 3rd instar caterpillar, early in this stage, length: 8mm.

A 3rd instar caterpillar, length: 12mm.

The 4th instar caterpillar has a head capsule which is black but with two whitish U- or V-shaped bands, one on each side of the head. The body is whitish-yelow with a green undertone. This instar lasts about 3 days with the body length reaching up to 21mm.

Two views of a 4th instar caterpillar, early in this stage, length: 12.5mm.

Two views of a 4th instar caterpillar, late in this stage, length: 20mm.

The 5th instar caterpillar features a head capsule which is whitish in ground colour and has two large black spots on each side of the head. The periphery of the head is marked with a broad black band. The anal plate is unmarked as in the all previous instars. This penultimate instar takes about 5-6 days to complete with the body length reaching 33-34mm.

Two views of a newly moulted 5th instar caterpillar, length: 19.5mm.

Two views of a 5th instar caterpillar, late in this stage, length: 34mm.

The 6th and final instar caterpillar has a strongly whitish body which has numerous tiny dark spots carpeting the surface. Two sub-dorsal bands run lengthwise along the body length. Compared to the previous instar, the whitish area in the head capsule has now enlarged so much that almost the whole head capsule is white. The two black oval spots are now smaller, and the black bands lining the periphery are broken into short stripes/bands. This final instar takes about 7-8 days to complete with the body length reaching 50-51mm.

Two views of a 6th instar caterpillar, early in this stage, length: 31mm.

Two views of a 6th instar caterpillar, late in this stage, length: 50mm.

Towards the end of 5th instar, the body of the caterpillar shortens in length and body colour assumes a uniform shade of dull 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 short transverse silk band are then spun. Once the caterpillar attaches its claspers to the transverse silk band, it enters the dormant prepupatory phase which lasts about one day.

A pre-pupa of the Conjoined Swift lying dormant in the pupation shelter.

The pupa secures itself with the silk girdle and with its cremaster attached to the transverse silk band. It has a short thorax, a rather long abdomen and a pointed rostrum. The body is dull green in the thorax and wing case but yellowish green in the abdomen. Narrow, whitish, sub-dorsal bands run lengthwise on the abdomen. Length of pupae: 37-38mm.

Two views of a pupa of the Conjoined 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 Conjoined Swift.

A newly eclosed Conjoined 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, 2nd Edition, 2015.

Text by Horace Tan, Photos by James Chia, Anthony Wong, PF Loke, Frederick Ho, Khew SK and Horace Tan

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