Autumn Invertebrates in the Perth Region

Main Club 5 April 2024

Our speakers this time were two young naturalists from the DRB, Andrew Wallace and Charles Porter. They told us some surprising facts about some invertebrates that can be found in autumn.

Charles took the floor first. We learnt why witchetty grubs – the larvae of Swift Moths – eat so much and get so fat. It’s to give the adult plenty of fat to start with because it has no mouth and doesn’t feed at all. Grass Darts are butterflies that look like moths because of their dull colours and appearance when resting.

Naturalists and photographers Fred and Jean Hort have studied a newly described Neolucia butterfly. It was thought to be rare, but having found that its primary food source is Daviesia angulata, they searched among this species and found that it is quite common. 

Neolucia butterfly
– Image by Charles Porter

Its tiny larvae had been hard to find without knowing where to look. Amazingly, they live inside ants’ nests, and the ants take them outside during the daytime to feed so that they can milk them for their honeydew.

 The male Feather-horned Beetle has huge, branched antennae to detect the female’s pheromones. In the US, their larvae prey on cicadas, but whether they do this in Australia is unknown. Male and female Bird of Paradise Flies look completely unalike. The male looks like a feathery dandelion seed and is attracted to the fat, flightless female by the pheromones that she produces. She then inverts the end of her abdomen and lays her eggs inside her own body!

Andrew then spoke. Jewel Beetles (Buprestidae) have wood-boring larvae. After 1 to 20 years, the adult emerges from the pupal stage and lives for only a week or so. One species, the Fire Beetle Merimna atrata, is omnivorous and will even eat carrion. It forages in recently burnt bush, which has the advantage of being relatively predator-free. Also, the plants’ defences against wood-boring insects disappear after a fire. Infra-red receptors on its abdomen help it to avoid the hottest places. 

Australian Bull Ants are a unique and primitive group. They don’t lay chemical trails like other ants but rely on eyesight. Unlike most ants, they hunt individually. It’s the sting that hurts—not the bite. They have two stomachs and can regurgitate to feed other ants. Termites are social insects, but they are much more closely related to cockroaches than to ants. They have no larval stage. They start a colony when it rains in autumn (if it does!!) or spring. 

Andrew finished by talking about centipedes. Venom is injected by the first pair of legs – not by the jaws. Those big terminal legs at the back end are used mainly as decoys to hold down prey. Centipedes in WA are not considered dangerous despite their painful bite. Some underground species of centipede eat worms. Centipedes are good parents – they guard their eggs. But sometimes they eat them!

Mike Gregson