Glasswing

Acraea andromacha andromacha (Fabricius)

andromacha adult

Interesting Aspects

This is an unusual butterfly in which the forewings are transparent like glass, hence the common name. It has a slow graceful gliding flight, but if disturbed can make off with great speed. The slow flight is typical for poisonous species of butterflies that gives predatory birds sufficient time for recognition. The butterfly is readily visible in flight. Males are often seen hill topping. Both sexes are easily approached during normal flight.

The entire life history of this butterfly is poisonous. Its passion-vine hostplants contain poisons which the larva of the glasswing is able to assimilate and retain in its body as a protection against vertebrate predation. These poisons are cyanogenic glycosides, which release hydrocyanic acid when ingested. The poisons are passed on to the pupa and the adult butterfly. The latter can further top up its poisons by imbibing (sucking and assimilating) the sap and surface exudates from from other poisonous plants. The cardiac glycoside poisons are passed onto the eggs by the female to complete the cycle. These poisons are usually in sufficient concentrations to only sicken the vertebrate predators, so that they can both learn from the experience and pass on the knowledge. They are not meant to cause death as this would likely result in larger numbers of the butterfly being killed.

The butterfly belongs to a subfamily group within which most of the included butterflies and their early stages are poisonous, providing models for mimic butterflies. The early stages have characteristic shapes. The adult butterflies usually have bright wing colours. Members of the Acraea generic group are well developed in Africa, from where the single Australian species probably had its evolutionary origin. They are closely related to the Heliconiids in the Americas.

Life History

How a butterfly grows into an adult.

Larval Food Host

Hybanthus aurantiacus (shrub violet) (Violaceae); native Passiflora, also some introduced *Passiflora including *Passiflora (Tacsonia) mollissima (banana passion) (Passifloraceae).

Eggs

Eggs are laid on the undersides of the hostplant leaves, sometimes in very large batches of 200 or more eggs, and sometimes several females will also lay on the same leaf being stimulated by the previous efforts of the other females, such that huge numbers of eggs may eventually occur.

Larvae

Pupae

Flight Period in South Australia

The butterfly is seen all year round in the tropical north of Australia. During seasons with abnormal humidity it will move south during the hot months, occasionally reaching South Australia and Victoria.

Distribution

Normally a tropical and subtropical butterfly with vagrant tendencies. It is rarely seen in South Australia. It has been documented twice from Leigh Creek in the northern Flinders Ranges, during April 1976 and again 23 November 2010 (Trace & Liz Connolly). The other was from suburban Adelaide where a small breeding colony had become semi-established on a banana passion-vine (*Passiflora (Tacsonia) mollissima) during the abnormal summer humidity of the 1973-1974 season. The colony had died out by the following summer, possibly because most of the specimens became collectors items, but more likely because the butterfly is biologically unsuited to the winter conditions of South Australia. However, banana passion is not commonly grown in Adelaide and the butterfly would have had difficulty further establishing itself. The common edible passion vine Passiflora edulis, is toxic to the larvae of this butterfly, although the female butterfly will lay eggs on it, and it is therefore further possible that any surviving fertile females from the original colony could have expended all their eggs on these vines. A single specimen has also been documented from Broken Hill during November 1976.

map_acraea.gif (9.26 KB)
Habitat

It prefers tropical and subtropical humid forest and woodland habitat. A potential native hostplant Hybanthus aurantiacus (shrub violet) occurs sporadically in the extreme far-north of the state and it is possible that small opportunistic populations of the butterfly may occur in that area after good summer rain. Native Passiflora species do not occur naturally in South Australia.

Conservation Status in South Australia

A vagrant. Very common in the north of Australia.

Threats

No major threats.

Conservation Strategy

None required.