Birdwing

Birdwings are large, tropical papilionid butterflies native to mainland and archipelagic Southeast Asia and Australasia (with one Indian species), and are usually regarded as belonging to three genera: Ornithoptera, Trogonoptera and Troides. Some authorities include additional genera and the number of species range between 10 and 30 depending on the taxonomic treatment. Birdwings are named for their exceptional size, angular wings, and birdlike flight.

Included among the birdwings are some of the largest butterflies in the world: the largest, Queen Alexandra's Birdwing (Ornithoptera alexandrae); the second largest, the Goliath Birdwing (O. goliath); and the largest Australian butterfly, the Cairns Birdwing (O. euphorion). Another well-known species is Rajah Brooke's Birdwing (Trogonoptera brookiana), a particularly attractive species named after Sir James Brooke, the first White Rajah of 19th century Sarawak.

With the exception of O. alexandrae, all birdwings are listed in Appendix II of CITES as either vulnerable or rare, and accordingly their trade is restricted in countries party to the CITES convention. Exceptions are made for captive-bred specimens which are marketed through the Insect Farming and Trading Agency of New Guinea.[1] However, O. alexandrae is totally protected (Appendix I: endangered) and cannot legally be sold. This species is now known to be more common than previously thought and at the 2006 meeting of the CITES Animals Committee it was recommended that this species be relegated to CITES II, so allowing commercial exploitation of this butterfly.

Adult physical description

Birdwings are typified by large size (up to a maximum body length of 7.6 cm or 3 inches and a wingspan of 28 cm or 11 inches in O. alexandrae), showy coloration (in contrasting shades of green, yellow, black, white, and sometimes blue or orange), and slender, lanceolate forewings. With few exceptions (i.e., the New Guinean O. meridionalis and O. paradisea), the hindwings lack tails. Sexual dimorphism is strong in Ornithoptera species only, with females appreciably larger and less colourful than males.
Males and females of most Troides birdwings are similar and have jet black to brown dorsal forewings, often with the veins bordered in grey to creamy-white. At least one of these darkly-coloured species (T. rhadamathus) possesses thermoreceptors on the anal veins (A2 and A3) of the wings and on the antennal clubs. The antennal receptors of the clubs—which also possess hygroreceptors that measure atmospheric humidity—are known as sensilla basiconica. The thermoreceptors are sensitive to sudden increases in temperature; they are thought to help the butterfly thermoregulate and avoid overheating while basking.

The colours of most species are pigmentary (via papiliochrome); but two species, Troides magellanus and the much rarer T. prattorum, are noted for their use of limited-view iridescence: the yellow of the dorsal hindwings is modified by bright blue-green iridescence which is only seen when the butterfly is viewed at a narrow, oblique angle. This "grazing iridescence" is brought about through diffraction of light (after back-reflection) by the wings' extremely steeply-set, multilayered rib-like scales (rather than the ridge-lamellae of most other iridescent butterflies, such as Morpho species). Such limited-view iridescence was previously only known from one other species, the lycaenid Ancyluris meliboeus. In A. meliboeus, however, the iridescence is produced by ridge-lamellar scales and features a wider range of colours.

The close evolutionary relationship between Triodes and Ornithoptera butterflies is well demonstrated by the fact that commercial breeders have produced numerous hybrid specimens between the two.

Life history

Birdwings inhabit rainforests and adults are usually glimpsed along the forest periphery. They feed upon—and are important long-range pollinators of—nectar-bearing flowers of the forest canopy, as well as terrestrial flowers, such as lantana. They are strong flyers and seek sunlit spots in which to bask.

Breeding behaviour varies little between species: the female's role is relatively passive, slowly fluttering from perch to perch while the male performs an elaborate, quivering yet stationary dance 20–50 cm above her. After mating, females immediately begin to seek appropriate host plants; climbing vines of the genera Aristolochia and Pararistolochia (both in the family Aristolochiaceae) are sought exclusively. The female lays her spherical eggs under the tips of the vine's leaves, one egg per leaf.

The caterpillars are voracious eaters but move very little; a small group will defoliate an entire vine. If starved due to overcrowding, the caterpillars may resort to cannibalism. Fleshy spine-like tubercles line the caterpillars' backs, and their bodies are dark red to brown. Some species have tubercles of contrasting colours, or pale "saddle" markings. Like other members of their family, birdwing caterpillars possess a retractable organ behind their heads called an osmeterium. Shaped like the forked tongue of a snake, the osmeterium excretes a fetid terpene-based compound and is deployed when the caterpillar is provoked. The caterpillars are also unappealing to most predators due to their toxicity: the vines which the caterpillars feed upon contain aristolochic acid, a poisonous compound known to be carcinogenic in rats. The feeding caterpillars incorporate and concentrate the aristolochic acid into their tissues, where the poison will persist through metamorphosis and into adulthood.

Birdwing chrysalids are camouflaged to look like a dead leaf or twig. Before pupating, the caterpillars may wander considerable distances from their host plants. In O. alexandrae, it takes ca. four months to get from egg to adult. Barring predation, this species can also survive up to three months as an adult.