Great balls of spitfires

By Nikki Galovic, Juanita Rodriguez

16 November 2018

3 minute read

Sawfly larvae gather in groups to appear larger, deterring potential predators. Photograph by Gnangarra.

Remember when your teachers would tell you to keep away from the big tree in the back corner of the oval because of spitfires? In our young minds we imagined miniature dragons spurting fire at any poor soul that got too close. Some of the braver (or stupider) kids might have poked the strange mass of insects with a long stick and then run for their lives. But have you ever heard of spitfires since primary school? There are even myths that spitfires were just something teachers made up to scare children. Well we’re here to tell you that they do indeed exist and, aside from the fact that they don’t literally spit fire, what they’re all about.

Larvae child

The term spitfire is most commonly a slang term for several species of sawfly larvae from the family Pergidae. Despite the name, the larvae are not from a fly at all but actually a wasp with four wings and no stinger. And the larvae, while they might look like it, aren’t really caterpillars. The baby sawfly larvae make their homes in gumtrees feeding on eucalyptus leaves and gather in large clusters to appear larger and help protect themselves from predators like birds. The larvae grow to a length of about 5 cms. They pupate in a dark brown cocoon in the leaf litter, and the pupal duration can be two or three years before an adult wasp emerges.

Despite their caterpillar-like appearance, this sawfly larvae won’t grow into a beautiful butterfly.

Spit it out

Spitfires don’t actually spit, they dribble. When threatened, they wriggle their tails and regurgitate from their mouth a thick mustard-coloured goop that is made of concentrated eucalypt oils that they collect from their diet, and looks like fire. Despite our fears, spitfires, their goop and the grown sawfly are harmless to people and animals.

Part of the trouble of common names over scientific names is that they often get confused for multiple species. For example, some people use the term ‘Spitfires’ for an actual caterpillar – Doratifera vulnerans (also known as the mottled cup moth), which sticks out stinging hairs when disturbed. These little grubs don’t actually spit anything either, but the sting from the hairs can feel a bit like a burn which could be how they got the nickname.

I saw an ancient fly

Sawflies are probably closest to the ancestral form that all hymenopterans (ants, wasps, bees and sawflies) evolved from, which lived about more than 250 million years ago. Scientists at the Australian National Insect Collection are actually studying sawfly fossils from NSW that lived in the Jurassic, when dinosaurs were around! Their name comes from the female’s saw-like egg-laying tube, which she uses to make a slit in a plant leaf or stem, into which she lays her eggs.

Adult sawflies are distinct from wasps due to the broad connection between the abdomen and the thorax.

Most sawflies are females and like all other wasps lay fertile eggs without mating. Girl power! These eggs turn into male sawflies. When sawflies mate -however- they produce females. The eggs hatch in two to eight weeks to form small spitfires. Once the spitfires reach a peak size, they crawl down the tree and burrow in the soil where they use their goop to create a cocoon and incubate for a few months. Then, if they’re lucky, the bug emerges as a sawfly, but only lives for around seven to nine days. Why is that so lucky? It’s because of parasitic wasps. Parasitic wasps lay eggs in or on spitfires and once these eggs mature the parasitic wasps’ babies eat the spitfire. Bleak.

So next time you see kids swarming around a spitfire party, you can look like the bravest person in the world and confidently stroll up to the mass of bugs without a care in the world. You could also explain to the kids the bugs are harmless but then you’d lose your hero status and help end the myth that has perpetuated through the ages!