About this time of the year clumps of Sawfly larvae are commonly seen clustering on eucalypt branches.
These are actually the larvae of a wasp that has a saw-like device that they use to slit open bark and leaves to insert their eggs.
Larvae congregate in groups in daylight hours for protection. When disturbed they jerk up their heads and tails and emit a foul yellow fluid smelling of eucalyptus or other oil. This is a small boy’s delight (well it was for me but I can’t vouch for the smartphone generation). At night they move in procession to young shoots, which they systematically strip of leaves.
I have seen eucalyptus sawflies in Foxes Lair in autumn, but apparently other species attack Callistomen, Callitris, Ficus, and Leptospermum.
More information - http://australianmuseum.net.au/Sawflies