Caterpillar Conga Line
Occurred on February 25, 2017 / Umuwa, South Australia
Info from Licensor: "I recently moved to Umuwa in Central Australia to work with Indigenous Australians in the Anangu Pitjantjatjara Yankunytjatjara Lands (pronounced ar-nan-oo pigeon-jar-uh yank-uh-jara) lands to work as an indigenous ranger coordinator, helping local people protect cultural sites and the environment. The place is teaming with life, despite being in the middle of a desert. I spotted the line of caterpillars one morning and my first thought was "what's that rope doing in my garden" followed closely by "why is it moving?" On closer inspection I found it was a line of caterpillars walking head to tail in single file. Turns out they're pretty common up here, called processionary caterpillars (Ochrogaster Lunifer). During the day the caterpillars shelter communally in a bag nest made of silk, excrement, shed skins, and other debris."
Sometimes the nest is located on a shoot at the end of a branch, or sometimes high on the trunk.
The caterpillars feed mostly on acacia (wattle) trees and Grevillea striata (Beefwood). 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. If disturbed, they curl up defensively into a tight bunch.
If two caterpillars each locate a silk trail left by the other, the pair will follow each other, and so will walk around in a circle. If a whole group does this, then they can end up in a circular mass.