These caterpillar-like pests gather in groups and threaten predators with poisonous spit, giving them their common name – spitfires. But would you be able to recognise the wasp-like adults, the sawflies?
Common name: Sawflies (adult), Spitfires (larvae)
Scientific name(s): Hymenoptera of the suborder Symphyta.
Description: Unlike their relatives in the other Hymenopteran suborder (Apocrita – ants, bees, and wasps), adult sawflies lack a ‘wasp waist’ and have a comparatively thick connection between thorax and abdomen. Many sawfly species mimic wasps with their markings, and the saw-toothed ovipositor that gives them their common name may resemble a sting. Their antennae, depending on species and sex, may be simple, clubbed, feather-like, or forked.
Sawfly larvae – ‘spitfires’ – resemble caterpillars, with a distinct head capsule, three pairs of true legs and six or more pairs of fleshy prolegs. The more commonly-seen Pergid species have a body covered in short sparse bristly hairs that taper to a pointed tail. The bramble sawfly, Philomastix xanthophilus, has two tails. Some species like the cherry slug, Caliroa cerasi, cover themselves in a translucent slime.
Spitfires may gather on plants by their hundreds, rearing up and disgorging noxious eucalyptus oils if disturbed and leave the tree en masse when seeking dry soil or leaf litter to pupate in.
The female in most species will open a slit in the host plant with their serrated ovipositor, and lay her eggs inside. In some species she can lay fertile eggs without mating. Depending on the species of sawfly, larvae may live weeks or months before pupating, but adults are generally short lived.
Geographic distribution: Over 8000 species worldwide, and several hundred in Australia, covering some 25 families. Some exotic species have become pests in Australia, or were introduced to control certain weeds, while others were originally native to limited parts of Australia but have become pests elsewhere.
Habitat: Most species feed on plants as larvae, and are short-lived nectar feeders as adults. Species can be highly selective about which host plant they will feed on, with native species feeding on native plants. Some sawflies are parasites of wood boring insects
Pest status: Some species like the bottlebrush sawfly, Pterygophorus cinctus, and the cherry slug are garden pests, and may skeletonise and defoliate mature tees, and kill small ones. The eucalyptus leaf-blister sawfly, Phylacteophaga froggatti, is an eastern states species that has become a pest in Western Australia, eating the insides of eucalyptus leaves and seriously weakening young trees.
The noxious chemicals regurgitated by Pergid sawflies can irritate skin or eyes, but are not as poisonous as common folklore suggests.
Treatment: Spitfires may be removed by hand, or controlled by natural predators, parasites, and diseases. Biological and chemical insecticides, and insecticidal soaps and oils, may also be effective, if used as directed. Severely damaged or leaf-mined foliage may have to be pruned.
Daniel Heald, technician and entomologist (image credit: Daniel Heald)