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NEWS RELEASE No: 1457013 APRIL 2011

Moth pest caterpillars now emerging in Berkshire and West London

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Oak processionary moth (Thaumetopoea processionea) larva

Residents of Pangbourne in Berkshire and parts of west London are being cautioned not to touch the caterpillars of the pest oak processionary moth (OPM) that are now hatching out in oak trees there. They are also being asked to report any sightings.

The caterpillars are a forestry pest and can be a health hazard. They damage oak trees by feeding on the leaves, and their tiny hairs contain a toxin that can cause itchy skin rashes as well as eye and throat irritations.

Forestry, health and local authorities are dealing with outbreaks of the moth in five boroughs of West London and in Pangbourne, near Reading in West Berkshire.

Since the species was first found in Pangbourne in 2010 the Forestry Commission and West Berkshire Council have begun efforts to eradicate it from the area before it can spread further, as well as to protect local people from the health risks.

It has also become established in the London Boroughs of Ealing, Brent, Hounslow, Richmond upon Thames and Hammersmith & Fulham, since it was found there in 2006. Eradication from this area is now considered impracticable, so the Forestry Commission’s policy is to work to contain it within those boroughs. The Commission is therefore surveying a 10-kilometre (6-mile) buffer zone around the infested area, and will require the removal of any caterpillars or nests in the buffer zone. Control within the infested area is the responsibility of tree owners and local authorities.

Stewart Snape, deputy head of the Forestry Commission’s Plant Health Service, said the public could help, although he urged people not to touch the caterpillars or their nests.

“We welcome reports of caterpillars or their nests from the public or others, such as gardeners and tree surgeons, who are out and about in areas with oak trees,” he said.

“However, the public should not try to remove the caterpillars or nests themselves. These jobs need to be carefully timed to be most effective, and are best done by specially trained and equipped operators.”

Dr Brian McCloskey, director of the Health Protection Agency in London, endorsed this advice for health reasons, saying:

“We strongly advise people not to touch or approach the caterpillars or their nests because of the health risks caused by the toxin-containing hairs. Pets can also be affected and should be kept away as well.

“Anyone who experiences an itchy skin rash or other allergic symptoms after being near oak trees in these areas should consult their GP.”

Mr Snape also asked people who were having oak trees pruned or felled in either of the affected areas to contact the Forestry Commission’s Plant Health Service beforehand on or 0131 314 6414 for advice about safe removal of the material.

Sighting reports should include a precise description of the location. An Ordnance Survey grid reference is ideal, otherwise an accurate postal address with the full postcode, and/or a clear description of the tree's exact position, is helpful. Digital photographs may also be sent as an aid to identification.

  • Sighting reports - can be sent to Forest Research, part of the Forestry Commission, on 01420 22255 or, or to the local council (see Notes to Editor for contact details).
  • Health advice - Anyone who is worried by an intensely itchy or painful skin rash, sore throat and irritated eyes, and who might have been near oak trees harbouring OPM, should consult their GP or call NHS Direct on 0845 4647. Health information is also available from
  • Pest control - A list of local pest control operators qualified to deal with OPM is available from the Forestry Commission on 0131 314 6414 /, or the local Council (see Notes to Editor for Council contact details).

Further information is available from


1. Sightings can be reported to, and lists of pest control operators requested from, the following Council contacts:

2. The best time to tackle the moth is in the spring, after the caterpillars have hatched, and in the summer when they gather in their distinctive white, silken nests to pupate into moths. Over the next few weeks surveyors will be looking for and mapping trees with caterpillars in them in Pangbourne and the London buffer zone. Pest control operators will then remove them. Later in the summer they will also remove and destroy nests made by any remaining caterpillars, which would pupate in the nests before re-emerging as moths.

3. OPM (Thaumetopoea processionea) gets its name from the caterpillars' habit of moving about in nose-to-tail processions. A native of southern Europe, it most likely entered Britain as over-wintering eggs on semi-mature trees imported for landscaping projects.

4. Nests are always dangerous to approach because of the presence of the caterpillars’ toxic hairs. The peak danger period for human health is from mid-May to the end of June.

5. The caterpillars pupate in their nests in late June and early July and emerge as moths between one and four weeks later. The moths lay their eggs in oak trees in July and August, and the eggs hatch caterpillars the following spring. The caterpillars feed in groups, and at other times congregate in communal nests made of matted, white silk webbing - typically about the size of a tennis ball.

6. The caterpillars do not necessarily kill trees - they usually recover - but they would add another unwelcome stress to Britain's oak trees, which in some areas are already suffering from other stresses such as acute oak decline.

7. A native of southern Europe, it has become established as far north as The Netherlands over the past 20 years. Climate change might be a factor: fewer and less-severe late spring frosts, which could kill emerging caterpillars, might have improved its chances of survival in more northern latitudes.

8. The species will attack other broadleaved trees such as hornbeam, hazel, beech, sweet chestnut and birch, but usually only where they are close to severely defoliated oaks where the preferred food of oak leaves is limited.


  • Forestry Commission / Forest Research - Charlton Clark, 0131 314 6500;
  • West Berkshire Council – Arthur Cullen, 01635 519675;
  • Ealing Council – Neelum Bains, 020 8825 6323; 
  • Richmond upon Thames Council - Pete Leriche, 020 8891 7160;
  • Brent Council – Gavin Martin 020 8937 1067 or Jason Grimsley, 020 8937 5430; 
  • Hounslow Council - Jini Amarasekara, 020 8583 2186;
  • Hammersmith & Fulham Council – Jonathan Weisgard or Rob Mansfield, 020 8753 2163;
  • Health Protection Agency - Tycie West or Emily Collins, 020 7811 7243/7242;
  • Royal Botanic Gardens, Kew - Anna Quenby, Bronwyn Friedlander or Bryony Phillips, 020 8332 5607,
  • The Royal Parks – Frances Therrien, 0300 061 2128.