Oak Processionary

The wingspan of adult stage moth is between 25 and 35 millimetres (0.98 and 1.38 in). Their pattern of tan, brown and white makes the adults difficult to see against oak bark. Adults fly during July and August. The larvae construct communal nests of white silk from which they crawl at night in single file, head to tail in large processions to feed on foliage in the crowns of trees, returning in the same manner. Oak is its preferred food source, but the moth also eats the leaves of hazel, hornbeam, sweet chestnut, birch and beech.

The moths are widely distributed in central and southern Europe, and are occasionally found as far north as Sweden. In the southern countries of Europe the populations are controlled by natural predators, but these predators are not present in northern Europe. Their range is expanding northward, possibly or partly as a result of global warming. The moth now has an established population in the UK. The eggs arrived on oak imported to the Richmond and Ealing areas of London in 2006 and the range of the species in the UK has been steadily expanding despite efforts to eradicate it. In Ireland, an outbreak of oak processionary moth was detected in June 2023 but was successfully eradicated. Ireland subsequently retained its Protected Zone status, with the pest officially recorded as "Absent, pest eradicated" following official surveys.