Pine Processionary

Description:

It's a Pine Processionary's nest: it's one of the most destructive species of pines and cedars in Central Asia, North Africa and the countries of southern Europe. The urticating hairs of the caterpillar larvae cause harmful reactions in humans and other mammals. The species is notable for the behaviour of its caterpillars, which overwinter in tent-like nests high in pine trees, and which process through the woods in nose-to-tail columns, protected by their severely irritating hairs

Notes:

The caterpillars are highly social. At first they are nomadic, spinning and abandoning a series of flimsy shelters constructed by enveloping a few needles in silk but in the third instar they initiate the construction of a permanent nest and settle down to become central place foragers. There are no definitive openings in the shelter that allow the caterpillars to enter and exit. Rather, the caterpillars force their way through the layers of the shelter as they move in and out. The frass that is produced as the caterpillars process their meals accumulates at the bottom of the shelter.