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February 2011

Clustering ‘caterpillars’

Can you identify the caterpillars that are gathered together in a clump and eating the leaves of our gum tree? When we disturbed them they ‘pulsed’ all together at about a human heart rate. Are they dangerous at all?


The ‘caterpillars’ in your photos are the larvae of sawflies, a type of primitive wasp. If you look closely you can see the larvae have six or more prolegs (fleshy leg-like structures at the front of the body). Butterfly and moth caterpillars never have more than five prolegs.

These wasps are called ‘sawflies’ because the females have a saw-like tip to their ovipositor (egg-laying apparatus) which they use to insert their eggs into plant tissue.

There are 176 known species of sawflies in Australia and the largest family, Pergidae, contains 140 species. The adults are solitary insects; however their larvae can be extremely gregarious.

‘Spitfires’ are the most well known of these social larvae. Spitfire larvae feed at night and move together in a writhing cluster. When searching for fresh foliage they keep in touch with each other by ‘tapping’ their tails. If disturbed while resting during the day, they rear up their heads and regurgitate a repugnant fluid, which has given them the name spitfires.

Fully grown larvae leave their feeding trees en masse to pupate in the soil. The adult wasps can take a year or more to emerge.

 Further reading:

  • Living Insects. R.D. Hughes. William Collins, Sydney, 1974.
  • Wildlife of Australia. Densey Clyne. Reed New Holland, 1999.

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