Magellan Birdwing (Troides magellanus)

In this guide

1. Description and identification
2. Life cycle: egg, caterpillar, chrysalis and adult
3. Where the Magellan birdwing lives
4. Host plants and diet
5. Behavior: flight, courtship and conservation
6. Similar butterflies and how to tell them apart
7. Quick facts
8. Did you know?
9. Frequently asked questions

Description and identification

The Magellan birdwing is one of the giant swallowtail butterflies, placed in the tribe Troidini, the group whose caterpillars all feed on poisonous pipevines. Its genus, Troides, contains the golden birdwings of Southeast Asia, and this species is the one restricted to the Philippines and to a single small island off Taiwan. Two subspecies are recognised: Troides magellanus magellanus in the Philippines and Troides magellanus sonani on Orchid Island. Despite the name, no birdwing has tails; the "swallowtail" family label refers to the group, not to this butterfly's wing shape.

Adult butterfly

• Wingspan: males span about 5–6 in (13–15 cm) and females about 6–7.5 in (15–19 cm). Older accounts credit the female with a ten-inch span; that figure belongs to Queen Alexandra's birdwing, and no reliable measurement of this species reaches it.
• Male upperside: forewings velvety black with pale grey streaks lying between the veins, and hindwings a deep golden yellow crossed by black veins and closed by a black outer border carrying a row of separate black spots.
• The blue flash: the male's golden hindwing is not simply pigmented. Viewed from in front and slightly below, as it would be by a butterfly flying behind it, the gold turns to an iridescent blue-green or violet sheen. This angle-dependent effect is produced by the fine structure of the scales and is the single most distinctive feature of the species.
• Female upperside: larger and duller. The wings are dark chocolate-brown to blackish, the forewing carrying pale grey-white streaks along the veins and the hindwing a chain of cream to golden submarginal spots separated by dark veins.
• Body: black head and thorax with a patch of crimson-red hair on the underside of the thorax, a bright yellow abdomen, and stout black antennae. The red thoracic patch is a warning signal shared with other pipevine-feeding swallowtails.
• Sexes: strongly dimorphic. Size, ground colour and the amount of gold all differ, so males and females are easy to tell apart, which is not true of most butterflies on this site.

How to identify a Magellan birdwing in the field

Size and flight come first: a butterfly the size of a small bird, beating slowly and gliding between forest trees, can only be a birdwing. Then look at the hindwing. Solid gold panels bounded by black veins and a spotted black border, on a black-winged male, point to this species, and the blue-green flash as the angle changes confirms it. The female is identified by elimination, from her size, dark brown wings and the chain of pale spots along the hindwing margin.

Life cycle: egg, caterpillar, chrysalis and adult

Development from egg to adult takes roughly two to three months in warm lowland forest and longer at altitude or in the dry season. Breeding follows the rains, when the pipevines put out the soft new growth the young larvae need.

Eggs

The female lays her eggs singly or in small groups on the underside of pipevine leaves and on nearby stems, hovering beside the vine and curling her abdomen under the leaf. Each egg is spherical, about 2 mm across, and pale orange to yellow, usually coated in a thin layer of protective secretion that dries to a rough finish. A female lays on the order of two to three dozen eggs over her life, far fewer than a small butterfly produces, and they hatch after about a week to ten days.

Caterpillar

The caterpillar is blackish-red to brownish-orange and carries five lengthwise rows of soft, fleshy, spine-like tubercles down its body, with a broad white or cream band across the middle segments that breaks up its outline. Like every swallowtail larva it has an osmeterium, a forked orange gland that shoots out from behind the head when the caterpillar is touched and releases a sharp, unpleasant smell. Its real protection, though, is chemical: pipevine leaves contain aristolochic acids, and the larva stores them, so it is poisonous to birds and remains so as a pupa and as an adult. Well-grown larvae eat whole leaves and will strip a small vine, and they sometimes chew through a stem so that the part beyond it wilts.

Chrysalis

The full-grown caterpillar leaves the vine and pupates on a twig, stem or the underside of a branch. The chrysalis is light brown to yellowish-beige with darker mottling and a leaf-like outline, so it passes for a dead, curling leaf hanging in the undergrowth. It is held upright against its support by a hook at the tail and by a loop of silk around the middle, the girdled posture typical of swallowtails, which is quite different from the head-down hanging pupa of a brush-footed butterfly. The adult emerges after about a month, and pupae formed at the start of a dry season may wait considerably longer.

Adult

Birdwings are long-lived by butterfly standards. Adults survive for several weeks and up to roughly three months in favourable conditions, feeding daily and mating repeatedly, which is why old accounts that give the lifespan as unknown are worth updating; our guide to how long butterflies live sets that figure against the two or three weeks most butterflies manage.

Where the Magellan birdwing lives

The species has one of the smallest ranges of any birdwing. The nominate subspecies is spread across much of the Philippine archipelago, including Luzon and several of the neighbouring islands, while the subspecies sonani is confined to Lanyu, the small volcanic island off southeastern Taiwan known in English as Orchid Island. Nothing in between holds the species, and the Taiwanese population is separated from the Philippine one by open sea.

Its habitat is closed, humid forest. It occupies lowland and submontane dipterocarp forest and the mossy forest above it, keeping to primary and well-grown secondary stands from near sea level up to roughly 5,000 ft (1,500 m). Adults favour the sunlit edges of this forest, natural clearings, ridge tops and the margins of tracks, where flowering trees and shrubs grow within reach and where males can patrol. The butterfly needs two things in the same place: pipevines climbing in the understorey for its caterpillars, and nectar-rich flowers for the adults, and both are casualties of clearance, which is why the species thins out sharply in heavily logged country.

Host plants and diet

Caterpillar host plants. Like all birdwings, the Magellan birdwing depends entirely on pipevines of the genus Aristolochia, with Aristolochia tagala the best known host across its range. These woody climbers are laced with aristolochic acids, compounds that damage the kidneys of vertebrates and deter almost every other leaf-eating insect. The larva tolerates them and stores them, converting a defended plant into a personal chemical shield. The relationship is strict enough that the butterfly cannot be reared on anything else, and conservation of the species is in practice the conservation of its vines.

Adult diet. Adults drink nectar and nothing else of consequence. They work the flowers of Hibiscus, Lantana, Ixora, Mussaenda, Bougainvillea and flowering forest trees, usually in the early morning and late afternoon, and they feed with the wings still beating rather than settling fully, so that a heavy butterfly does not have to trust a slender flower stalk. That constant fluttering at a blossom is one of the easiest birdwing behaviours to recognise from a distance.

Behavior: flight, courtship and conservation

Flight. The flight is slow to moderate, powerful and unmistakably bird-like, with deep, unhurried wingbeats and long glides on flat wings. Males fly a regular beat along forest edges, ridges and stream courses during the first hours of daylight, checking flowering trees along the way and often returning by the same route. Females fly lower and more slowly, searching the understorey for pipevines, and they are seen far less often than males.

Courtship. When a male overtakes a female he hovers above and slightly behind her, fanning scent from specialised scales set in the fold of his hindwings down over her antennae. It is during this hovering approach, from the female's viewing angle, that the blue-green iridescence of his hindwings is displayed, and the effect is generally read as a courtship signal rather than an accident of the scale structure.

Defence. A butterfly this large, slow and conspicuous would be easy prey if it were edible. The aristolochic acids carried over from the caterpillar make it bitter and toxic, the golden hindwings and red-haired thorax advertise the fact, and the unhurried flight is itself part of the message: a bird that has tried one birdwing does not try a second.

Conservation. Every species of Troides is listed on Appendix II of CITES, so international trade in specimens is regulated and requires permits. The main pressure on the Magellan birdwing is not collecting but the loss of lowland and submontane forest across the Philippines, together with the clearing of the understorey vines it cannot breed without. Butterfly farms in the Philippines rear the species on cultivated pipevines, which supplies the specimen trade and takes pressure off wild populations, and the butterfly is a regular exhibit in walk-through houses worldwide.

Similar butterflies and how to tell them apart

Quick facts

Did you know?

• The blue-green sheen on the male's golden hindwings appears only within a narrow range of viewing angles, which is why it is missing from most photographs and from every pinned specimen seen flat in a drawer.
• The butterfly is named for Ferdinand Magellan, whose expedition reached the Philippines in 1521, and it was formally described in 1862 by the Austrian father-and-son entomologists Cajetan and Rudolf Felder.
• Aristolochic acid, the compound that protects the caterpillar, is toxic to human kidneys, which is why the pipevines the larvae eat are restricted as herbal medicines in many countries.
• Birdwings lay remarkably few eggs for their size. A female may produce only two or three dozen in her life, against several hundred for a similar-sized moth, and she invests in large, well-provisioned eggs instead.
• The Taiwanese population on Orchid Island is a protected subspecies and one of the few birdwings found outside the tropics proper, at the very northern edge of the group's range.
• Other giant swallowtails share its forests and its pipevine habit, among them the great Mormon and, further south and east, the electric-blue Ulysses butterfly and the golden Wallace's golden birdwing.

In summary

The Magellan birdwing, Troides magellanus, is a giant swallowtail of the Philippines and Orchid Island whose males have velvety black forewings and golden hindwings edged with a spotted black border, and whose larger, chocolate-brown females carry a chain of cream-gold spots instead. Males span 5–6 in and females 6–7.5 in, not the ten inches sometimes quoted. The caterpillar is dark red-brown with rows of fleshy tubercles and a white band, feeds only on Aristolochia pipevines and stores their toxins; the leaf-like brown chrysalis is girdled upright to a twig; and the adult flies slowly through forest clearings for weeks or months, flashing blue-green from its gold hindwings as the angle changes. It is protected under CITES Appendix II, and its future depends on the survival of Philippine forest and the vines beneath it.

Frequently asked questions about the magellan birdwing butterfly

What does the Magellan birdwing caterpillar look like?

The caterpillar is blackish-red to brownish-orange with five lengthwise rows of soft, fleshy spine-like tubercles and a broad white or cream band across the middle of the body. Behind the head it carries an osmeterium, a forked orange gland that everts and gives off a sharp smell when the larva is disturbed.

Where is the Magellan birdwing butterfly found?

It occurs only in the Philippines and on Lanyu, or Orchid Island, off southeastern Taiwan. The Philippine populations belong to the subspecies Troides magellanus magellanus and the Orchid Island population to Troides magellanus sonani. The two are separated by open sea, and the species is absent from the mainland of Asia.

How big is the Magellan birdwing?

Males span about 5 to 6 inches (13 to 15 cm) and females about 6 to 7.5 inches (15 to 19 cm), making it one of the largest butterflies in the Philippines. Claims that the female reaches ten inches confuse it with Queen Alexandra's birdwing of Papua New Guinea, which genuinely does.

How do male and female Magellan birdwings differ?

Strongly. The male has velvety black forewings and solid golden hindwings bordered with black spots, and shows a blue-green flash at certain angles. The female is larger, with dark chocolate-brown wings, pale grey streaks on the forewing and a chain of cream-gold spots along the hindwing margin instead of a solid golden panel.

Why do the male's wings flash blue-green?

The golden scales of the hindwing are microscopically structured so that light striking them at a glancing angle is reflected as blue-green or violet rather than gold. The effect appears mainly when the butterfly is viewed from in front and below, the angle a following female sees during courtship, and it disappears in flat light.

What does the pupa of a Magellan birdwing look like?

The chrysalis is light brown to yellowish-beige with darker mottling and a leaf-like outline, so it resembles a dead curling leaf. It sits upright against a twig, held by a hook at the tail and a silk girdle around the middle, the arrangement typical of swallowtails. The adult emerges after roughly a month.

What habitat does the Magellan birdwing prefer?

It lives in closed, humid forest: lowland and submontane dipterocarp forest and the mossy forest above it, from near sea level to about 5,000 feet. Adults concentrate along sunlit forest edges, clearings and ridge tops where flowering trees grow, and the understorey must hold pipevines for the caterpillars.

Is the Magellan birdwing poisonous?

Yes, to predators. Its caterpillars feed on Aristolochia pipevines and store the aristolochic acids those plants contain, so the larva, the pupa and the adult are all bitter and toxic to birds. The butterfly cannot bite or sting and is harmless to handle, and its bright gold and red markings advertise the chemical defence.

Are there different subspecies of the Magellan birdwing?

Two are recognised. Troides magellanus magellanus is the Philippine subspecies and Troides magellanus sonani is confined to Orchid Island off Taiwan, where it sits at the northern limit of the birdwing group. They differ in small details of the golden hindwing markings and in the width of the black border.

Is the Magellan birdwing protected?

Yes. Like every species of Troides it is listed on Appendix II of CITES, so international trade requires permits. The greater threat is habitat loss, since clearance of Philippine lowland and submontane forest removes both the nectar sources and the Aristolochia vines the caterpillars must have. Licensed butterfly farms rear it on cultivated vines.