Steel-blue Sawfly - Perga dorsalis


This page contains pictures and information about Steel-blue Sawflies that we found in the Brisbane area, Queensland, Australia. 

Body length 25mm
Steel-blue Sawfly looks like a stout body wasp. Steel-blue Sawfly is dark brown in colour with yellow spots on shoulder and on thorax. The legs are orange in colour. The orange antenna are relatively short. 
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On Dec 2008, we saw this Steel-blue Sawfly on gum leaves. Look closely we saw some scratched marks on the leaf surface. We believe the sawfly was trying to cut open the leaf surface by it saw-tooth like ovipositor and will lay some eggs inside the leaf. This sawfly was very slow moving. It did not move a bit even we watched very closely. 
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From reference information, Adult sawflies do not feed. They live for 1-2 weeks during which time they lay their eggs. Most of the sawfly adults are females, males are rare. Mating is not necessary for sawfly for the production of fertile eggs.  
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Steel-blue Sawfly larvae are pied in blue-black colour when young. They become all blue-black when matured. The head is black in colour. They feed on gum leaves. They store eucalyptus oil inside body used for deference. They aggregate on leaves, branches or trunks by days, disperse and feed during the night. They pupate in dark brown cocoon in soil and leaf litter.  
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Steel-blue Sawfly larvae are also known as 'spitfires' as they can eject an irritating fluid from their mouth. This defence method ensures predators avoid them. When disturbed, larvae tap their abdomens up and down and regurgitate the thick yellow fluid. The above pictures show the larvae before and after disturbed.  

1. What wasp is that? - An interactive identification guide to the Australasian families of Hymenoptera, 2007.
2. Steel-blue sawflies - Australian Museum.
3. Perga dorsalis Leach, 1817 - Australian Caterpillars, Don Herbison-Evans & Stella Crossley, 2008.
4. Spitfires - Defoliating Sawflies - PIRSA Forestry, 2010. 

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Last updated: October 18, 2010.