Tirumala hamata hamata (W.S.
Macleay) (Blue Tiger or Blue Wanderer)
Interesting aspects: A large, distinctive butterfly, similar in size and shape to the related orange Wanderer butterfly. Both sexes are similar, but males can be distinguished by the presence of a large, raised silvery-grey sex pouch in the lower-centre of each hindwing. The males also have a pair of grey "hairpencils" enclosed near the tip of their abdomens, which they can protrude and expand into a feather-like mop and dispense a characteristic scented pheromone that is required for successful courtship.
It is essentially a tropical butterfly with migrant tendencies. During the dry (winter) season when the larva hostplants are in short supply, the butterflies mass together in very large colonies in cool, shady areas, usually along moist creek lines. These groups can contain thousands of butterflies in which the females are reproductively dormant. Individual butterflies have been reported to survive for 5 months or more during this period. When the wet (summer) season breaks and the hostplants begin to flourish, the females become reproductive and disperse to the breeding grounds in the coastal vine thickets. As numbers again buildup, full of fat reserves, many fly southwards as migrants. Along the eastern seaboard of Australia they can reach as far south as eastern Victoria. They can form local semi-resident breeding colonies as far south as northern NSW, but further south they are biologically unsuited to the cooler conditions. During favourable, moist summers, some of these migrations occur further inland, and have been recorded at Mt Isa and Broken Hill.
The entire life history of the butterfly is poisonous, in varying degrees. Its milkweed hostplants contain poisons, which the larva is able to isolate and retain in its body as a protection against vertebrate predation. These poisons can be 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 the hostplant again, or from other poisonous plants. From the latter the male butterfly obtains further poisons (pyrrolizidine alkaloids), which are necessary for the production of the hair-pencil pheromones. The pyrrolizidine poisons are also emitted as a defence mechanism through the hair-pencils when the male butterfly is attacked, or even when it is roughly man handled. 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 or at least taste unpalatable, so that the predators can learn from the experience and pass on the mistake. They are not meant to cause death as this would likely result in larger numbers of the insect being killed.
In northern Australia the flight is normally slow and graceful, but if disturbed the butterfly can make off with great speed. The slow flight is typical for poisonous species of butterflies, which gives predatory birds sufficient time for recognition. Both sexes are easily approached during normal flight.
Larval food-host: Larvae feed on tropical milkweed vine plants of the Asclepiadaceae family, including species within Cynanchum and Marsdenia, none of which grow naturally in South Australia. Those species that do grow in SA such as Cynanchum floribundum (native pear) and Marsdenia(Leichhardtia) australis (native pear) are apparently not utilised as hostplants. The toxicity of each plant species varies. The poisonous properties of native milkweeds are not well known, although Marsdenia poisons include alkaloids. Larvae normally feed on the leaves and young shoots, which are often quickly demolished, and the larvae will then eat stems, fruit pods and even exposed roots of the vines. The demolition of the northern tropical hostplants then probably forces the adult butterflies to migrate, to seek new areas of hostplants.
Flight period: The butterfly is seen all year round in the tropical north of Australia. It flies south during the southern warmer months, occasionally reaching as far south as Victoria. A number of migrating butterflies were recorded flying east in the Broken Hill area during February and March of 1974 during a season of abnormal summer humidity.
Distribution: Normally a tropical butterfly with migrant tendencies, moving south into subtropical latitudes during the warmer months. The butterfly has yet to be observed in South Australia, but as it has been seen migrating near Broken Hill, 65 km east of the SA border, there is a good chance a similar migration will be seen in the poorly surveyed northeast part of SA in the future, during an extended wet monsoon summer period.
Habitat: It prefers tropical and subtropical humid forest and woodland habitat. The butterfly is biologically unsuited to South Australian conditions.
Conservation Status: A migrant. Locally common in the tropical north of Australia.
Threats: No major threats.
Conservation Strategy: None required.
Author: R. GRUND, © copyright 3 March 2003, all rights reserved.
Last update 3 March 2003.