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Oak processionary moth - Thaumetopoea processionea

The Oak Processionary Moth (Thaumetopoea processionea) is native to central and southern Europe. Adult male moths have occasionally been found along the south coast of England and also on the Channel Islands, where they have presumably either flown in or been blown across from the Continent. It gets its common name from its caterpillars' striking habit of forming long lines, or ‘processions’, in trees and other substrates.

  • Photo
    Oak processionary moth larvae aggregating on trunk of an oak
    London, May 2007
  • Photo
    Group of oak processionary moth larvae feeding on an oak
    London, May 2007
  • Photo
    Defoliation of oak by oak processionary moth larvae
    London, May 2007
  • Photo
    Defoliation of oak by oak processionary moth larvae
    London, May 2007

In 2006 it was found in west London along a stretch of the A40 and in Kew and East Sheen. This was the first recorded breeding population in Great Britain.

Health risks

The caterpillars have urticating (irritating) hairs that carry a toxin which can be blown in the wind and cause serious irritation to the skin, eyes and bronchial tubes of humans and animals. They are considered a significant human health problem when populations reach outbreak proportions, such as those in The Netherlands and Belgium in recent year.

You must not attempt to handle the larvae caterpillars yourself, or disturb their nests.

Tree damage

The caterpillars can also cause serious defoliation of oak trees, their principal host, but the trees will recover and leaf the following year. On the Continent they have also been associated with hornbeam, hazel, beech, sweet chestnut and birch, but usually only where there is heavy infestation of nearby oak trees.

As with many moth species, population levels tend to vary from year to year, peaking from time to time. Although a native of southern Europe, the moth spread northwards during the latter half of the twentieth century. It was first recorded in The Netherlands in 1991, and subsequent reports of damaged trees indicate that numbers have soared, with 1996 and 2001 being particularly bad years for tree damage. Populations declined between those years, but are again reaching very damaging levels in The Netherlands and neighbouring areas of Belgium.

Further information

Addresses to contact if you think you have seen this insect

Report possible sightings of the caterpillars or their nests/webs to your local Council (Brent, Ealing, Hounslow or Richmond Upon Thames) or Forest Research (above), who will take the necessary action.

The contact details are:

If you find nests or caterpillars outside these areas, contact:

You must not attempt to handle the larvae caterpillars yourself, or disturb their nests.