Steel Blue Sawfly: Perga dorsalis

Perga dorsalis Leach, 1817
Steel Blue Sawfly
PERGIDAE, SYMPHYTA, HYMENOPTERA

Don Herbison-Evans
(donherbisonevans@yahoo.com )
and
Stella Crossley

(Photo: courtesy of Merlin Crossley, Melbourne, Victoria)

These are not true Caterpillars, but are the larvae of a wasp, or more accurately a Symphytan. When young, these larvae are so gregarious they are often found in a knotted ball of many individuals. When disturbed, they all wriggle their tails and exude a nasty yellowish fluid from their mouths.

(Photo: courtesy of Sharon Adnum, Bowral, New South Wales)

This latter habit has given them the common name of "Spitfires", although they do not actually spit the fluid, just dribble it. They use the tapping of their tails to communicate with each other.

(Photo: courtesy of Aura)

They have a blue-black body, sometimes with white areas, with the body tapering towards the tail. The larvae are covered in short white bristles.

(Photo: courtesy of the Macleay Museum, University of Sydney)

The larvae are often found feeding on:

Gum Trees ( Eucalyptus, MYRTACEAE ).

Other Sawfly species feed on other plants.

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 years.

(Specimen: courtesy of the Macleay Museum, University of Sydney)

An adult insect (it is misnamed as a 'fly') is big and dark brown or black, with a white spot on the thorax, and a wing span of about 4 cms. The female lays her eggs in a slit she cuts between the upper and lower surfaces of a leaf of a food plant.

The larvae and adults of this family are quite harmless to people. They do not sting, as their cousins the communal wasps do.

This species can be found in

Tasmania, and

Various species of Sawflies are ubiquitous, being found in :

Australia, and

the rest of the world.

Further reading :

William Elford Leach,
Descriptions of new, or interesting animals,
The Zoological Miscellany,
London : E. Nodder & Son, Vol. 3 (1817) p. 117, sp. 4, and also Plate 148, fig. 1.