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Oak Processionary Moth

Credit: Forestry Commission

Credit: Nigel Straw - Forestry Commission

Credit: Stephen Middleton - Observatree Volunteer

Credit: Stephen Middleton - Observatree Volunteer

Pest or disease?
Pest

Latin name:
Thaumetopoea processionea

Host trees:
Oak trees (Quercus sp.)

Present in the UK?
Yes, mainly in and around London

Tree Alert required?
Yes

Oak processionary moth, often called OPM, was accidentally introduced to the UK in 2005.

OPM is native to central and southern Europe but has spread across northern Europe, possibly aided by the trade and movement of live oak trees. The OPM caterpillars feed on the foliage of oak trees and their hairs can irritate our skin, so it is important not to touch or approach the caterpillars or their nests. The UK government is currently running a surveillance and control programme to try and minimise the population and spread.

OPM caterpillars feed on oak leaves, causing defoliation. They are identifiable by their distinctive movement, moving from their nest to feeding areas in processions. They form a line, sometimes multiple caterpillars wide and move together. Their nests can also be seen on branches or the trunk of the tree. They are made from white silk-like material and range from the size of a golf ball to a rugby ball. The caterpillars and nests are seen in late-spring and summer. The adult OPM moth is rarely seen and difficult to identify. For more information on OPM please see the resources below.