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NEWS RELEASE No: 1625430 APRIL 2014

Push on to eradicate Oak processionary moth from Pangbourne

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White, silken nest of oak processionary moth (Thaumetopoea processionea) on trunk of oak tree

Forestry and local authorities are gearing up for another push to eradicate the oak processionary moth (OPM) from oak trees in the Pangbourne area.

OPM caterpillars can be a hazard to the health of oak trees, people and animals, but there are indications that they might be close to being eradicated from the area’s oak trees: no nests were found in Pangbourne oak trees in 2013, compared with four in 2012 and 61 in 2011.

However, five adult male moths were found, so the Forestry Commission and West Berkshire Council are carrying out another spring and summer control programme to prevent another generation from developing.

Alison Field, Forestry Commission Area Director, explained,

“Although the captures of five adult male moths do not necessarily mean that a viable breeding population is still present, they do indicate that the pest had not been completely eliminated from the area.

“Eradication from Pangbourne is our goal, and these results indicate that we are getting close to it. We cannot afford to give the population a chance to recover if we are to ensure that local people can continue to safely enjoy their parks, gardens and woodlands.”

Operations will include two aerial treatments of two areas of Sulham Woods, which are public woods managed by the Forestry Commission. Ms Field explained,

“Our scientists advise that the moths are most likely to have come from oak trees in these areas, and we must presume that some OPM is still present, and treat the trees.

“Access difficulties make it almost impossible to inspect or treat them effectively from the ground, so we will use a helicopter to achieve the accuracy and degree of treatment needed.”

Oak trees close to the other three sites where moths were found, and at two sites where nests were found in 2012, will be treated from the ground.

Ms Field gave an assurance about the operations’ safety, saying the most commonly used treatment product is not known to harm people, pets, livestock, crops and garden plants. It is especially formulated to affect only a small number of caterpillar species, and that populations of any other species affected are expected to recover. Modern guidance systems make helicopter spraying extremely precise, and this, combined with avoidance of windy days, should ensure minimal drift on to surrounding land.

The parts of Sulham Woods to be treated will be closed as a safety precaution while the helicopter is working. The exact dates will depend on the weather, but the Commission will keep local people informed via its website, local news media and its Twitter account,

Ms Field urged local people to help by watching for signs of OPM, such as the caterpillars’ distinctive nose-to-tail processions, and their white, silken webbing trails and dome- or teardrop-shaped silken nests in oak trees. These become discoloured after a few days. Sightings should be reported to the Commission via its Tree Alert app or on-line form, by email to, or to West Berkshire Council.

She also urged people not to approach the caterpillars or nests, and to train or restrain their pets from doing so, to avoid the health risks from contact with the caterpillars’ hairs.
Further information is available from, or from the Commission’s public enquiry line, 0845 FORESTS (0845 367 3787).


  1. OPM was first discovered in Pangbourne in 2010. It is a native of southern Europe, where local predators and environmental factors keep its numbers in check. It is believed to have been accidentally introduced as eggs laid on oak saplings before they were imported from continental Europe for planting.
  2. OPM larvae, or caterpillars, are a hazard to tree, human and animal health. They feed on oak leaves, and large numbers can strip whole trees bare, leaving them vulnerable to other threats. Their tiny hairs contain a protein which on contact can cause itching skin rashes, eye and throat irritations and, occasionally, breathing difficulties.
  3. Herridge’s Copse, a Pangbourne woodland and Site of Special Scientific Interest (SSSI) which was treated by helicopter in 2013, will not be treated again unless new evidence of OPM presence is found. The parts of Sulham Woods to be treated are not within an SSSI.
  4. The treatment product most often used to control OPM infestation is called Bt, and is derived from a naturally occurring bacterium called Bacillus thuringiensis.
  5. OPM will be deemed to have been eradicated from Pangbourne once two seasons have passed with no evidence of its presence being found.
  6. A full report on the 2013 OPM control programme in Pangbourne and London, where there are two other outbreaks, is available at

Media contacts:

  • Forestry Commission - Charlton Clark, 0300 067 5049
  • West Berkshire Council - Peta Stoddart-Crompton, 01635 519670.