OPM is harmful both to trees and to people
Oak processionary moth (Thaumetopoea processionea) is a native of southern Europe. Due to trade in live plants, oak processionary moth has become established as far north as the Netherlands and northern Germany. It was first introduced to Britain in 2005 accidentally.
Regular monitoring of oak trees is recommended so that caterpillars can be identified early to prevent a full-blown infestation. If you have, or suspect you may have, oak processionary moth in your garden, please do not touch or approach the nests or caterpillars. Given the health risks, the Forestry Commission advises contacting a pest management expert to ensure safe removal.
A professional arborist will know what to look for, including the hairy caterpillars along with the tell-tale signs of plaques on a tree's branches. For more info, visit Bartlett Tree Experts' Oak Processionary Moth pest detail page.