Plain tiger (Danaus chrysippus): mimicry, milkweed and a near-global range

The plain tiger, Danaus chrysippus, is a brownish-orange butterfly widespread across Africa, Asia and Australia, with populations also on south Pacific islands, in Southern Europe and in Kuwait. It belongs to the family Nymphalidae, in the same genus as the monarch, and its caterpillars feed on milkweeds and other toxic plants. Three subspecies share out this huge range: alcippus across most of Africa, chrysippus through Asia and parts of Africa, and orientis in tropical Africa, Madagascar and the Seychelles.

Identification

The plain tiger is a mid-sized butterfly with a wingspan of about 75 mm. The upperside is brownish orange, brighter and richer than the underside. On the underside, the apical half of the forewing is black with a white band, the hindwing carries three black spots in the centre, and the wings are bordered in black and outlined with semicircular white spots.

The sexes are easy to tell apart. The male has large scent glands on his hindwings, which appear as a large black spot with a white centre when viewed from below; the female lacks them entirely. Those glands hold pheromones the male needs for courtship, built from chemicals he gathers as an adult rather than inherited from his caterpillar diet.

Range and habitat

The species’ range runs from Africa and Asia to Australia and the Pacific islands. It favours arid, open habitats from sea level to about 1,500 m: deserts, mountains, deciduous forests, and gardens and parks in cities; it avoids dense jungle. That tolerance of dry, disturbed and even urban ground is a large part of why the plain tiger has spread so far, turning up in gardens and roadsides as readily as in wilder country.

Life cycle and host plants

Caterpillars feed on Asclepiadoideae (milkweeds), chiefly Asclepias and Calotropis, along with other plants in the Apocynaceae, Plumbaginaceae and Moraceae. These plants supply the cardenolides that make both caterpillar and adult distasteful to predators, though some West African populations store the compounds poorly in adulthood yet still manage to repel predators.

The egg is tiny, about 1.7 mm long and 0.5 mm across, and normally hatches within 3 to 5 days. The caterpillar, striped yellow and black, passes through five instars over 12 to 20 days before pupating; the pupa itself takes 9 to 15 days, changing colour from pale green to dark brown as the adult inside develops.

Behaviour and flight period

Adult males visit wilted or dead plant stems to drink pyrrolizidine alkaloids, chemicals they cannot make themselves but need to build the pheromones used in courtship; in Australia, sources include Echium plantagineum, Heliotropium amplexicaule and Parsonsia species. This habit of visiting damp patches of ground and plant debris to take up fluids and minerals is common among butterflies and is known as mud-puddling.

The plain tiger’s warning colours have made it a model for other butterflies rather than just a mimic of its own kind. Several palatable species copy its pattern to borrow its reputation for being inedible, among them Hypolimnas misippus, Pseudacraea poggei, Mimacraea marshalli and, in east Africa, some forms of Papilio dardanus: classic Batesian mimicry, which only works for as long as the mimics stay rarer than the plain tiger itself. In Uganda, Acraea encedon and Acraea encedana, which are themselves unpalatable, converge on a similar pattern in a case of Müllerian rather than Batesian mimicry.

Conservation

The species is listed by the IUCN under the category shown in the facts box, taken from its Wikidata record. A butterfly spread across so much of the Old World tropics and subtropics, and comfortable in disturbed and urban ground, faces no single pressure threatening it across its whole range.

Similar species

• Monarch (Danaus plexippus): its American counterpart in the same genus, also orange with black borders and white spots, and also unpalatable to predators thanks to a milkweed diet.
• Indian fritillary (Argynnis hyperbius): an unrelated species that coexists with the plain tiger across parts of its Asian range and can be mistaken for it at a glance.