The Wanderer or Monarch Butterfly is well-known in North America for its massive and wide-ranging migrations. In Australia, the species also makes limited migratory movements in cooler areas. It has only been present in Australia since about 1871.
Adult Wanderer Butterflies are orange-brown with black wing veins and a black and white spotted band along the edge of the wings. The caterpillar is distinctive, with black, white and yellow stripes across its body. It has two pairs of black tentacles - a longer pair at the front of the body and a shorter pair on the eighth body segment.
Wanderer Butteflies live in urban areas, where its food plants (e.g. milkweeds) are found.
The Wanderer Butterfly is found in eastern and southern Australia, in Queensland, New South Wales, Victoria (uncommon) and South Australia. They are commonly seen in Sydney during summer, usually flying at ground level. They have been recorded at speeds of up to 40 km per hour. The earliest sighting of this butterfly in Sydney was in 1871, although the population only became established when its food plants, including poisonous milkweed, were also introduced.
In summer, Wanderers are found throughout their range along the east coast of Australia from Queensland to South Australia, and in south-west Western Australia. They have also been found in isolated parts of the Northern Territory. They are strong fliers and can cover long distances during their adult life, which is about a month to six weeks in summer. During this time they can move to unoccupied areas to find new plants on which to lay eggs. They take nectar from flowers to maintain their energy levels as they go.
As winter approaches, the butterflies leave the inland areas as temperatures drop and migrate towards the coast. For Wanderers near the coast north of the Richmond River in New South Wales, breeding can continue for most of the year with one generation following another. Further south, adults that develop in autumn do not breed immediately. They remain in a non-breeding state throughout winter, some of them staying in the same district for several months.
In cooler areas, these non-breeding adults may gather together and hang from the branches of trees in large clusters of thousands of butterflies. This is known as over-wintering. The same trees are used for this year after year. The clusters are at first made up mainly of males. The females arrive a week or so later. During the warmth of the day the butterflies fly around the trees, but with the afternoon drop in temperature they settle to reform clusters. Cluster sites are known in the Sydney Basin and Hunter Valley, as well in the Mt Lofty Ranges, near Adelaide.
The clusters appear in about April and remain until about August or September, when the butterflies disperse after mating. The females are the first to leave, moving off to lay the first eggs of the new season on fresh spring growth. Succeeding generations extend the range across the country until the full summer range of the species is again occupied.
Feeding and diet
Wanderer Butterfly caterpillars are most often found on their preferred food plants (introduced food plants), which are from the milkweed family (Asclepiadaceae). These plants have a milky sap, from which the caterpillars derive distasteful toxins that deter predators from eating them. Some of these plants have become widespread environmental weeds and have allowed the butterfly to spread beyond urban centres (as seen in the distribution map). The caterpillars' bright colouration is a warning to these predators that they are potentially toxic. The adult butterfly is also toxic to most predators.
Other behaviours and adaptations
The poison from the plants is carried through the various stages of the Wanderer Butterfly's life cycle, making them unpalatable and causing many predators, including large birds, to be violently ill.
Life history cycle
Their life cycle includes a transition from eggs to adults during warm summer temperatures in as little as 25 days. However, this transition can extend to several weeks, during cool spring conditions.
Some predators appear to be unaffected by the Wanderer Butterfly's poison and birds such as the Pied Currawong (Strepera graculina) and the Black-faced Cuckoo-shrike (Coracina novaehollandiae) have been seen feeding on it.