Processionary Caterpillars - Also known as Bag Shelter / Brown Tails / Boree Moths (Ochrogaster lunifer). Anna's Reservoir, Northern Territory, Australia. Numerous caterpillars all walk head to tail touching the caterpillar in front and following a thread of silk laid down by the caterpillar in front. The hairs deter predators and if touched by humans induce intense irritation caused by poison glands at the base of each hair. Processions occur when they have totally defoliated a tree, usually an Acacia, and are looking for a fresh plant to eat or when they are seeking a suitable tree in which to build a bag and pupate. Aboriginal children are reputed to nudge the lead caterpillar around until it is touching the last caterpillar. Then the caterpillars will walk in a circle for some time. .