We have recently had a few cases involving oak processionary moth (OPM) caterpillars.
OPM caterpillars have hairs containing toxic compounds that irritate the eyes and mouth. Inquisitive pets that come into contact with the caterpillars or their nests may develop 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.
These caterpillars are most commonly found in the south east of England in the UK, and the main risk period is from April to July. They crawl in processionary lines (hence their name) which can make them intriguing to pets.