If you think you have spotted OPM you should firstly report any sightings to the Forestry Commission using their Tree Alert tool available from www.forestry.gov.uk/treealert or by email to opm@forestry.gsi.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 require. The nests must also be disposed of properly to avoid the pest spreading.

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.

A Spreading Concern

Presence of OPM caterpillars has already been confirmed in West and Southwest London with the pest spreading steadily to new areas. Careful monitoring of OPM spread is ongoing, but unfortunately all evidence indicates that this pest is slowly spreading beyond the London area.

Beyond the damage to trees, infestations are particularly concerning as these caterpillars pose a risk to human health. Each caterpillar has thousands of tiny hairs containing a toxic compound. Contact with these hairs can result in rashes, conjunctivitis, and breathing difficulties for people and animals.

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More Information

Life Cycle

The oak processionary moth life cycle includes egg, larval, and moth stages.


OPM caterpillars have a negative impact on tree health, and are harmful to humans and animals.


A variety of treatments are available to address affected trees.