Remember the grubs from hell?
Hi Christine
These are sawfly larvae, but they are not bottlebrush sawflies. They are true spitfires (subfamily Perginae), which are quite diverse and not easy to identify from the larvae (for examples of the diversity in this group see: http://www.brisbaneinsects.com/brisbane_sawflies/Perginae.htm).
The tapping behaviour that Christine has observed and filmed occurs in response to disturbance. The larvae also use this as a form of communication to reform the group after some individuals have become separated. Most species feed on eucalypts, and if the larvae are disturbed at close range on a tree, they will typically rear their heads back and exude a concentrated solution of eucalyptus oil. The larvae extract the oil from the leaves and then store it for the purposes of defence. There are two reasons for the larvae leaving their host plant as they have done in the supplied photograph. Firstly, if the plant that they were feeding on has become defoliated, the larvae will move elsewhere in search of an another food source. Alternatively, if the larvae are mature and ready to enter the next stage of development, they will leave the food plant and find a suitable place to burrow together (such as the soft organic matter at the base of a tree) before transforming into pupae. I suspect that in this case the larvae may be ready to pupate because they look quite mature, but it is hard to say for certain.
Thanks for your query and the video!! Actually would it be OK for us to use your video at the museum at some stage to show their interesting tail wagging behaviour? If so , could you confirm this be email reply.
Colleen
Colleen Foelz