ScienceTree Wardens

An update on the pest affecting the UK’s treasured oak trees

Harriet Rix, Science & Research Project Manager, June 2020

Oak Processionary Moth (OPM) is one of the pests and diseases that has been introduced to the UK in the past twenty years, and the TC Science and Research team are working with DEFRA on projects to understand and limit the damage it can do.

The hairy caterpillars of OPM pose little threat to the health of a sturdy oak tree – they could munch their way through three batches of leaves and the tree would still be able to produce more. However, the risk they pose to humans and animals is more severe as the hairs cause irritation and rashes. The problem is compounded with repeated exposure, and some tree surgeons who remove the caterpillar nests from oak trees have reported very serious symptoms.

The moth has thrived on oaks as a result of hot summers and warm winters, and although initially it was confined to London it is gradually spreading across the South of England. Last year some outbreaks were intercepted as far north as Inverness (see map attached), and although it is hoped that all the outbreaks were caught there’s a possibility that they may not have been.

What can I do to help?

Forest Research is tracking the presence of OPM via Tree Alert so if you see one of the distinctive lines of hairy caterpillars processing along an oak near you, please report it. (see ID guide here) And as ever, check all your trees for pests and diseases, and make sure you buy trees that are biosecure!