Scientific Name: Danaus plexippus (Linnaeus).
The Wanderer butterfly (Order Lepidoptera, Family Danaidae) is originally from North America and is known there as the Monarch butterfly. The earliest recorded sighting of the butterfly was in 1871 in Sydney. The population became well established only after its preferred species of milkweed plants were also introduced to Australia. Milkweed plants produce a toxic milky-white sap that can be seen when the plant is scratched. The Wanderer caterpillar feeds on the milkweed plants and ingests the toxic sap. The toxins are stored in the body and carried throughout the butterfly's life cycle, making both the caterpillar and the butterfly unpalatable to most predators. The brighly coloured striping on the caterpillar acts as a warning to predators, indicating that it is poisonous and unpalatable. If the warning colors are ignored, many animals usually learn by experience, as eating the caterpillar often makes them violently ill. That is not to say that Wanderers are predator free. The Pied Currawong (Strepera graculina) and the Black-faced Cuckoo-shrike (Coracina novaehollandiae) have been seen feeding on the butterfly without any ill effects.
Photo of Wanderer butterfly courtesy of Jennifer E. Dacey, University of Rhode Island. Image 0580012, www.insectimages.org.