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Oak processionary moth

This non-native moth has been found in London and Berkshire. It causes a risk to human health as well as seriously damaging trees.

What are oak processionary moths?

Oak Processionary Moth (OPM) is a recent introduction into the UK. It gets its name from the distinctive processing behaviour of the caterpillars because they tend to move in nose-to-tail lines. The caterpillars of these moths feed on oak leaves leading to severe loss of foliage which can weaken the trees and make them more vulnerable to other diseases. However, the main concern with this pest is the threat to human health because the caterpillar hairs can cause severe allergic reactions.

Where is it from?

  • Caterpillars of the oak processionary moth, Thaumetopoea processionea, are a native of central and southern Europe (see Forest Research guide to distinguishing it from similar native species)
  • Probably entered Britain as eggs laid on young trees imported from Europe for planting here.


  • Found in 2005 in London and now breeding in several locations in south and west London, and in West Berkshire – including several Woodland Trust sites
  • Milder weather and reduced late frosts could enable the moth to survive and breed further north than its traditional native range. Likely that it could survive and breed in much of England and Wales.

Health precautions

  • The oak processionary caterpillars’ tiny hairs contain a toxin which can lead to itching skin lesions and, less commonly, sore throats, breathing difficulties or eye problems. This can happen if people touch the caterpillars or nests, or if the hairs are blown into contact by the wind
  • For this reason, avoid contact with the nests and caterpillars – and keep pets and livestock away from them too
  • The nest may persist for several years. Please treat these with the same caution as a live nest
  • Adults and children must see a doctor immediately if they have come into contact with OPM and begin to suffer symptoms
  • If pets or livestock come into contact, they should be removed from the area and a vet should be contacted.

Report it

If you think you’ve spotted this disease please inform the Forestry Commission using the Tree Alert reporting tool. Three good-quality digital photographs are required to aid identification.

For further information visit the Forestry Commission.