What is an oak processionary moth caterpillar?
Caterpillars are oak processionary moth (OPM) at the larval stage of the insect’s life cycle.
They have thousands of hairs which can come off their bodies and are blown about by the wind. The hairs contain an irritating substance, called thaumetopoein, which makes pets and people itchy and can cause other problems (see below).
OPM caterpillars are found almost exclusively in oak trees and you can usually see them crawling around the branches or trunk in lines, nose-to-tail. They often cluster together and build white, silk-type nests in the branches or trunks (not in the leaves) of trees. Sometimes they walk along the ground between trees in this procession, which makes them intriguing to dogs. Unlike other caterpillars, they do not live on fences or walls.
They have some very long white hairs which are really noticeable among the rest of their much shorter hairs.
They are most likely to pose a risk to pets and people from May to July, but it’s best to keep away from them at all times.