Forestry Commission alert over Oak Processionary Moth


The Forestry Commission has issued an alert to people living in parts of London and Berkshire asking them to ‘be vigilant’ for caterpillars of the Oak Processionary Moth as they emerge between now and June. Together with Public Health England and the local authorities they are warning people not to touch the caterpillars and to keep children, pets and livestock away from them and their nests. 

The caterpillars are a tree pest because they damage oak trees by feeding on the leaves but pose a risk to human and animal health because they have tiny, toxin-containing hairs which can cause itchy skin rashes, eye and throat irritations and can trigger asthma attacks. The hairs can be blown on the wind and are also left in the web-like nests found in oak trees. The larvae leave the nests and feed on oak leaves, stripping each tree bare before moving to the next, following one another in a procession, hence their name. The caterpillars pose the greatest risk from now until July, although nests should not be approached at any time.

The Forestry Commission is working with local authorities and land managers to tackle the outbreaks and is appealing to the public to alert them to any sightings. Members of the public must not attempt to remove the nests or touch the caterpillars as protective clothing and masks need to be worn and the timing of removal is important.

Any sightings should be reported to the Forestry Commission using their online form at http://www.forestry.gov.uk/treealert or using their dedicated app available from https://itunes.apple.com/gb/app/tree-alert/id582936354?mt=8

Look out for:

Caterpillars in or near oak trees. There is an identification guide on the Forestry Commission website which will assist.

Web-like nests in oak trees or on the ground nearby. The white nests are the size of a tennis ball and contain hundreds or caterpillars each about two-inches long. Nests should be reported even if there are no caterpillars as they still contain the irritating hairs.

Check the tree species: The OPM caterpillar is usually only found in oak trees and will only live in and feed off other species of oaks are scarce.

Do not:

Observe the movement: OPM caterpillars have a distinctive habit, moving in nose-to-tail processions and clustering together. 

Touch or approach nests or caterpillars

Let children touch or approach nests or caterpillars

Let animals touch or approach nests or caterpillars

Try removing nests or caterpillars yourself – call an expert


Seek medical advice if you think you or someone you care for has been seriously affected

See a vet if you think your pet or livestock has been seriously affected

Call in a pest control expert to remove infestations in your own trees

Report sightings of OPM to your Local Council or the Forestry Commission.


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