Oak processionary moth (OPM) caterpillars have hairs containing a substance that irritates the eyes and throat. Inquisitive pets that come into contact with them may show symptoms such as excessive drooling, swollen tongue, conjunctivitis, gagging, vomiting, difficulty breathing or an inflamed or swollen mouth. The hairs can also come off their bodies and are blown about by the wind, potentially making nearby pets and people itchy. Generally symptoms are no more serious than irritating but very occasionally more severe allergic reactions can occur.
They are most commonly found in the south east of England in the UK, from May to July. They crawl around in processionary lines, nose-to-tail, which can make them intriguing to pets.
OPM caterpillars are found almost exclusively in oak trees and you can usually see them crawling around the branches or trunk in lines. They often cluster together and build white, silk-type nests in the branches or trunks (not in the leaves) of trees.
As the hairs of the caterpillar contain a hazardous substance, it’s a good idea to keep your pet (and yourself) away from them.