If they have totally defoliated their food tree, the caterpillars migrate to seek out another one, leaving a silk trail. When a caterpillar of the species encounters such a trail it will follow it, especially if there is a pheromone scent associated with it. There can be a hundred or more caterpillars in a head-to-tail procession, kept together by contacting the tail hairs of the caterpillar in front.