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NEWS RELEASE No: 1354028 APRIL 2010

Help us eradicate this pest

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Oak Processionary Caterpillars

Forestry and health authorities are once again reminding people not to touch the caterpillars of the oak processionary moth (OPM) that are now hatching in oak trees in west London, and asking the public to report any sightings.

The caterpillars, which are the larval life-stage of the moth, are pests that damage oak trees by feeding on the leaves. Their tiny, toxic hairs can cause painful skin rashes and irritations to eyes and ears and, in severe cases, breathing difficulties if they are inhaled. Animals can be similarly affected.

The affected boroughs are Ealing, Hounslow, Brent, Richmond Upon Thames and Hammersmith & Fulham. Since it was first identified in the London area in 2006, the Forestry Commission has been leading a group of authorities, including local councils and the Health Protection Agency, in an effort to contain the moth and eventually eradicate it before it can spread further.

The best time to tackle it 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 adult moths. Over the next few weeks surveyors will be looking for and mapping trees with caterpillars in them. They will be followed by specially equipped and trained pest control operators to deal with them. Later in the summer the operators will also remove and destroy nests made by any remaining caterpillars, which would pupate in the nests before re-emerging as moths.
Roddie Burgess, head of the Forestry Commission’s Plant health Service, said the public could help.

“We welcome reports of sightings of the 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.
“However, we strongly advise people not to touch or approach the caterpillars or their nests because of the health risks that the toxic hairs pose to them and their pets and livestock.

“Nor should they try to treat the caterpillars or remove the nests themselves. These jobs need to be carefully timed to be most effective, and are best done by specially trained operators.”

Mr Burgess also asked people who were having oak trees trimmed or felled in any of the affected boroughs 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 and photographs can be sent to Forest Research, the scientific research arm 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 itching skin rash, conjunctivitis or other symptoms, and who might have been near oak trees harbouring oak processionary caterpillars and their nests, should consult their GP or call NHS Direct on 0845 4647. Health information is also available from
  • Owners of affected oak trees can contact the Forestry Commission on 0131 314 6414 or, or their Council (see Notes to Editor), for a list of suitably qualified local pest control operators who can deal with them.
  • Further information is available from the Pests & Diseases area of


1. Sightings can be reported to the relevant Borough Councils as follows:

Sightings in Richmond Park can be reported to the park office, 020 8948 3209;

2. Oak processionary moth (Thaumetopoea processionea) gets its name from the caterpillars' habit of moving about in nose-to-tail processions. A native of southern and central Europe, it was first identified on oak trees in north-west and south-west London in 2006. It most likely came into Britain as over-wintering eggs on semi-mature trees imported for planting in landscaping projects. It began breeding in several locations there, including the Royal Botanic Gardens, Kew, and Richmond Park.
3. 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, when the hairs are most numerous.
4. 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.
5. 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.
6. Although a native of central southern Europe, it has become established as far north as The Netherlands over the past 20 years. Climate change might have been a factor: milder winters and, in particular, fewer and less-severe late spring frosts which could kill emerging caterpillars, might have improved its chances of survival in more northern latitudes.
7. 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.
8. About 700 nests were destroyed in 2007, 500 in 2008, and 2500 last year. Last year’s increase might have been due to the very favourable conditions for caterpillars of all species in 2009, and surveyors’ growing expertise in finding them. Despite last year’s nest numbers, no evidence was found that the species had spread beyond the five boroughs, and there was no significant change on 2008 in the numbers of adult males caught in pheromone traps after the nesting phase.


  • Forestry Commission / Forest Research - Charlton Clark, 0131 314 6500 or 07810 181067; 
  • Ealing Council – Claire Parker, 020 8825 6551; 
  • Richmond upon Thames Council - Pete Leriche, 020 8891 7160;
  • Brent Council - Peter Kendall, 020 8937 5321 / 3054; 
  • 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 7759 2834;
  • Royal Botanic Gardens, Kew - Anna Quenby, Bronwyn Friedlander or Bryony Phillips, 020 8332 5607,
  • The Royal Parks – Katy Murray, 020 7298 2128.