Early in the morning, large numbers of Banded Flutterer Dragonflies descend from high in the trees to lower branches where they sun themselves, raising their body temperatures for efficient functioning. During the late morning and afternoon, they flutter and soar over the water, alighting on the tops of the waterside vegetation.
They hunt on the wing, gathering in swarms when food is abundant and capturing flying insects in their legs which have bristles that interlock to trap the prey. The legs project forward so that the food can be easily moved to the mouth in flight.
A pair of large eyes covers most of the head, so that the animal can see in all directions with only a slight turning of the head. Each eye has thousands of individual lenses that give the dragonfly a mosaic image of the world.
Attached to the thorax (the mid-section of the animal) are two pairs of wings. These can beat out of synchronization, making the dragonfly very manoeuvrable. It is for these beautiful wings that, in 1842, Jules Pierre Rambur gave this species its name, ‘graphi’ referring to what looked like inky blue-purple writing on the ‘ptera’ (wings). Flying demands much energy which requires that oxygen is efficiently supplied to the muscles. The body wall of the thorax and abdomen have spiracles (small holes) that carry air via tubes to the wing muscles.
At about 10cm wingspan, these dragonflies are fairly typical of modern dragonflies but about 300 million years ago, dragonflies were much larger, some fossil dragonflies having 70cm wingspans! Insects make good fossils because the chitin in exoskeleton (the body wall) preserves well.
In Rhyothemis, the exoskeleton is not fully chitinized, perhaps to aid its buoyant flight.
The male and female fly in tandem, the male using special structures at the end of its abdomen to hold the female’s head. While in flight, the female bends her abdomen so that its end touches the middle of the male’s body, picking up sperm. Then she straightens up and they continue to fly in tandem as the female lays eggs on the surface of the water.
The eggs hatch about a week later and the larvae (called nymphs) live in the water, taking in oxygen from the water through gills that project from their guts.The nymphs feeding voraciously on small aquatic animals such as insect larvae and crustacea. They grow rapidly, repeatedly outgrowing their exoskeletons that are cast off by the process of moulting. Just prior to the final moult, the nymph climbs a plant into the air. There it undergoes its final moult and metamorphoses into a winged adult. Blood is pumped into the wing buds that soon expand into the beautiful lacy wings.
The purpose of the wing markings is unknown but a curious evolutionary convergence sees similar markings on a distantly-related dragonfly from North America: Celithemis eponina.
Rhyothemis graphiptera is found along the north and east coasts of Australia as well as Indonesia, Papua New Guinea and New Caledonia.
In 1999, Australia Post released a stamp featuring Rhyothemis graphiptera.
Dr Richard Rowe (James Cook University), John Hawking (Murray Darling Freshwater Research Centre) and Dr Günther Theischinger (Sydney) are gratefully acknowledged for their contributions to this information. Natalie Barnett (CSIRO Entomology) kindly chased some sources of information.
Text copyright © 2005 Kevin L. Blazé