Kate Taylor & husband Clint live on & manage our Bon Bon Reserve (SA). She recently noticed these creepy & dangerous sacks – home to Processionary Catepillars (Ochrogaster lunifer).
By day the caterpillars hide communally in these nests made of silk, insect poo, old skins & other debris. This stuff can cause bad skin rashes & even touching the caterpillars themselves can cause a bad reaction.
Feeding nocturnally, they leave each evening & at dawn return to their nest. You may see them in their weird processions during the day if they totally defoliate their food tree (often wattles or Beefwood) & are on the look out for another one or when they're ready to pupate (which they do away from their food tree in a silk cocoon in the ground).
As their name suggests they walk in long processions. Each caterpillar keeping in contact with the one in front. When they walk they leave a trail of silk, which helps them navigate back.
When a caterpillar of the species encounters such a trail it will follow it. There can be 100 or more caterpillars in a head-to-tail procession, kept together by contacting the tail hairs of the caterpillar in front.