These hairy, grey caterpillars are the larval stage of the bag shelter moth (Ochrogaster lunifer). During the day groups of 300 or more caterpillars hide together at the base of a food plant (often a wattle or gum tree) in a nest of silk, leaf litter and frass. As they move around, each one lays a trail of silk from the spinneret near its mouth. Other caterpillars of the same species follow the trail nose to tail, like a miniature freight train. These processions form either to find a new food source or a suitable pupation site on the ground. They live by the ‘safety in numbers’ rule. Together they present a formidable number of irritant hairs to predators, and they never get lost!
The adult moths are grey, with a yellow banded abdomen ending in a white tuft of hairs, and a wingspan of about 4cm (2″).
Burke’s Backyard does not advise anyone to touch processionary caterpillars, because their hairs can cause an itchy skin condition.