Spitfire Sawfly are not true caterpillars. They are the larvae of a wasp, or more accurately a Symphytan.
These larvae are gregarious. They are often found in a mass of many individuals on the ground or on Eucalyptus tree trunks. When disturbed, they exude a nasty smelling fluid from their mouths. This latter habit has given them the common name of "Spitfires", although they do not actually spit the fluid, just dribble it.
The larvae also are inclined to tap their tails in some form of communication with the group.