Oak Processionary Moth

Oak processionary moth, often called OPM, was accidentally introduced to the UK in 2005. The moth is native to central and southern Europe but has spread into northern Europe as far as Sweden and also into parts of the Middle East. The population spread has possibly been aided by the trade and movement of infested live oak trees as well as climate change.  

In the UK the hairy caterpillars of OPM feed almost exclusively on the foliage of oak trees and if infestations are extremely heavy, they can lead to severe defoliation. Both caterpillars and nests of OPM are seen between late spring and summer, with the harmless but rarely seen adult moths flying from mid-summer to autumn. The caterpillars are generally more active at night-time, but observations of their nests and their processions between trees during the daytime, are more common.  

The caterpillars create golf ball to rugby ball sized webbed nests within which they weave their irritating hairs. These nests are found on the trunks and branches of oaks, but dislodged nests can sometimes be discovered beneath the trees. The irritating hairs can cause allergic reactions to humans and some animals and therefore any suspect OPM nest or caterpillar should always be avoided.  

In their native range OPM has its own natural predators but these have yet to synchronise their population movement with that of OPM. It has therefore been up to the UK Government to conduct continuous surveillance and introduce a control programme designed to try and minimise its population spread. 

For more information about Oak processionary moth, see the resources below.