Larvae of the Australian sawfly known as spitfires.
Sawflies: a close relative of wasps
Sawflies, or spitfires, are related to wasps and can regurgitate eucalyptus oil they have extracted from gum leaves.
3 November 2008 | Updated 8 February 2013
Sawflies, or spitfires, are not flies but relatives of wasps and are in the Order Hymenoptera. They are noted for the large, tightly packed clusters of larvae of some species that can be seen clinging to stems or branches of gum trees during the day. Adults are rarely seen.
One of the best known species of sawfly in south-eastern Australia is the steel blue sawfly (Perga sp.). Its larvae are black and covered in short white hairs. The adults resemble large, stocky wasps but they don’t have a waist like wasps and they are usually a dark metallic blue with a wingspan of about four centimetres. They frequent the foliage of their host plants.
The female sawfly inserts her eggs into a leaf using her saw-like ovipositor. On hatching, the larvae feed together on the leaf edge, later forming clusters by day and feeding at night. Hungry larvae will migrate en masse to another tree if they run out of food.
Mature larvae descend from the tree and bury themselves in the ground to pupate. The larvae pupate in the soil during the summer months. Adult sawflies later emerge from the soil in autumn.
Larvae of Pergid sawflies communicate by tapping their tails. They feed on gum leaves, collecting eucalyptus oil and storing it in a sac off their foregut. Their ability to regurgitate this when disturbed has lead to the name spitfires, however, they don't spit.
Are they pests?
Sawflies have little overall effect on larger trees, but they can defoliate young saplings and smaller eucalypts. Clusters of larvae can be knocked, washed off or removed by hand and killed. The larvae are harmless and the adults, which are related to wasps, cannot sting.
Other Australian sawflies
Although the species of sawflies found on eucalypts are the best known, there are also species that live on other Australian natives such as Callistemon and Melaleuca.
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