The monsoon forests of northern Australia are an unusual place, rainforests that dry out so much for part of the year that many plants drop their leaves like deciduous trees in temperate latitudes. The region's life forms have been somewhat scientifically neglected, but recent expeditions to explore the butterflies and moths have revealed some treasures, including one remarkable species lost for more than a century.
In 1887, one of the relatively few efforts to collect the flora and fauna of northern Australia brought back a specimen of a rare moth. The species was identified as belonging to a genus known for the distinctive whistling sound the males make to attract mates.
Dr Michael Braby of the Australian National University told IFLScience the whistling is produced by raised structures on the forewings that make a clicking sound when they touch, which turns into a trill with the frantic speed at which the wings are vibrated. On a visit to Keep River National Park, Braby heard such a whistle and on investigation found an entire colony of the missing species. He dubbed it the mimetic whistling moth for its resemblance to certain unrelated moth species.
Braby and colleagues have published their findings in an Atlas of the region. “This is one of the most poorly known regions of Australia and in our work to establish some baseline information about the invertebrates here we identified 132 species of butterfly and 31 day-flying moths,” Braby said in a statement.
Some pockets, particularly the northwestern corner of the Northern Territory, are rich in species found nowhere else in the world, many of them quite unusual.
Examples include the sandstone grass-dart (Taractrocera psammopetra) and rock grass-dart (Taractrocera ilia), both of which feed on resurrection grasses. As the name suggests, these grasses flourish during the wet season, and fade to an apparently lifeless husk during the dry. It only takes 24 hours after rain, however, for them to spring back to life.
The butterflies can't get the nutrients they need from the grasses in their dry phase, so the caterpillars enter a state known as larval diapause, building a silken shelter and spending months inside with their bodily processes shut down until the rain comes. Although diapause allows insects to survive hard times elsewhere Braby told IFLScience he observed a new twist when he saw butterflies mating and laying eggs during the dry season. “I collected some of the eggs and was astonished the caterpillars hatched and built a shelter to enter diapause without eating.” Only when the rains came did the caterpillars feed.
The ecology is thought to be the remnants of much more widespread ecosystems that contracted in the face of climate shifts. They are further threatened not only by global warming and sea level rise, but large-scale development of Australia's “top end”, and introduced grasses that burn much more intensively than native species.