If you think you have seen OPM, you should firstly report any sightings to the Forestry Commission via TreeAlert or by email to opm@forestrycommission.gov.uk. They can then keep track of the outbreak.

Secondly, please do not try to remove the caterpillars or nests yourself. They need to be removed by an Arborist who has had the correct training and has the necessary equipment required. The nests must also be disposed of properly to avoid the pest spreading.

Life Cycle of Oak Processionary Moth


Eggs are laid from July to early September. Each female lays between 100 and 200 eggs on twigs and small branches in the canopy.


Oak processionary caterpillars can be found from April to June. There are six stages during the caterpillar feeding cycle with caterpillars getting progressively bigger during each stage.

Stages 1-3: Caterpillars are very small when they hatch, around 2mm long, and are still less than 1cm by the time they reach the third stage.

Stages 4-6: Caterpillars spin silken nests and the larvae eventually moult to the pupal stage within those nests. During this phase, larvae may also be seen massing on the trunks and branches of trees and moving in the characteristic processions that give the moth its common name.

Adult Moths

Adult moths have a wingspan of around 30-32mm and grey forewings suffused with white and some darker grey markings. This coloration provides an effective camouflage against the bark of oak trees on which the adults often rest.

Treatment Options at Key Life-Cycle Stages

There are different treatment options depending upon the life-cycle stage of the oak processionary moth. View a chart that shows recommended treatment options for each stage of OPM development.

Oak Processionary Moth Control Services

If you are looking to have your property treated by a professional, find a local Bartlett Tree Experts' office near you. Bartlett covers most areas in the UK that are affected by OPM, including the entire Greater London area.