21 November 2015

Life History of the Bengal Swift

Life History of the Bengal Swift (Pelopidas agna agna)

Butterfly Biodata:
Genus: Pelopidas Walker, 1870
Species: agna Wallace, 1866
Sub-Species: agna Wallace, 1866
Wingspan of Adult Butterfly: 32-36mm
Caterpillar Local Host Plant: Brachiaria mutica (Poaceae, common names: Para Grass, Buffalo Grass, Dutch Grass, Giant couch, Scotch Grass).

The upperside view of a male Bengal Swift.

A close-up view of the forewing upperside of a male Bengal Swift. The lower cell spot is minuscule in this specimen.

Physical Description of Adult Butterfly:
On the upperside, the wings are brown. 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 touch the brand at its lower end). The female has additional white spots in spaces 1b, consisting of one minute upper spot and one larger lower spot. The line drawn the cell spots would typically pass far from the spot in space 1b. On the underside, the wings are ochreous without a greyish tinge. The forewing have 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.

A male Bengal Swift.

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

The underside view of the same female Bengal Swift in the above picture.

Field Observations of Butterfly Behaviour:
The Bengal Swift is moderately common in Singapore. Easily confused with the similar-looking Small Branded Swift, the adults have been sighted at multiple locations including grassy wastelands, urban parks and gardens across the island. The adults fly with a swift, strong and darting flight.