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NEWS RELEASE No: 144641 MARCH 2011

Containment policy decided for oak processionary moth pest in London

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Oak processionary moth (Thaumetopoea processionea) adult

The Government is to move to a policy of containing the pest oak processionary moth within five West London boroughs where it has become established since it was first discovered in the area in 2006.

This decision follows scientific advice that it is no longer practicable to eradicate the species from the core outbreak zone. It is a forestry pest because its caterpillars severely defoliate oak trees, and a health hazard because the caterpillars have minute, toxic hairs which can cause painful skin and throat rashes and irritations in humans and animals.

The Boroughs comprising the core outbreak zone are Ealing, Brent, Hounslow, Richmond Upon Thames and Hammersmith & Fulham. From now on, any action to be taken to manage the moth’s impact in the core outbreak zone comprising the five Boroughs will be up to local authorities and tree owners. The Forestry Commission will no longer issue Statutory Notices requiring the owners of trees within the core outbreak zone to have the nests and caterpillars removed from their trees on the grounds of tree health.

The Commission will, however, monitor populations of the moth within the core outbreak zone to keep an eye on trends and to try to predict bad years when the population, which increases and reduces in cycles of several years, looks likely to reach serious levels.

The Commission will also:

  • annually survey a ‘buffer’ zone extending to a radius of 10 kilometres (6 miles) outside the core zone, and will serve Statutory Notices requiring tree owners to remove any infestations found in the buffer zone;
  • co-ordinate a programme to eradicate a small, isolated outbreak of the moth found in oak trees at Pangbourne, near Reading in Berkshire in 2010; and
  • follow up the 2010 discovery of a nest and moulted caterpillar skins in Sheffield to check whether any caterpillars survived and bred in oak trees there.

Roddie Burgess, Head of the Forestry Commission’s Plant Health Service, said,

“We fully understand that local people and organisations will be very disappointed that we are no longer pursuing a policy of eradicating oak processionary moth from West London.

“However, Ministers have accepted scientists’ advice that it is no longer practicable to try to eradicate it from the area, and have asked us to move to a policy of containment and management.

“We and our partners in the local authorities, the health authorities, the Royal Botanic Gardens Kew, the Royal Parks and other managers of large properties have been very successful over the past five years in keeping the impact of this pest to a very low level. However, our experience on the ground and the scientific advice indicate that it was going to be almost impossible to completely eradicate it.

“It is therefore clear that the wisest use of the available resources is to continue to work towards keeping it contained at the lowest practicable level within the current core outbreak area and to prevent it from spreading outwards to the rest of the country.”

To help keep the pest contained within the core zone, restrictions will be imposed on the movement of oak material, such as nursery plants and tree surgeons’ prunings, out of the core outbreak zone into anywhere else in Great Britain. Further information about these restrictions is available from the Commission’s Plant Health Service on; tel: 0131 314 6414.

More information about oak processionary moth is available from the Forestry Commission website at

Notes to editor:

  1. Management of an outbreak of oak processionary moth includes treating the caterpillars with insecticide at critical stages in their development during the spring, and removing and destroying their silken nests when any remaining caterpillars congregate in them in summer to pupate into adult moths.
  2. About 700 nests were recorded in the core outbreak zone in 2007, 500 in 2008, 2500 in 2009 and 2100 in 2010, and most were destroyed before adult moths emerged. The large increase in 2009 might have been due to the very favourable conditions for caterpillars of all species that year, and surveyors’ growing expertise in finding them. Despite the past two years’ increased numbers, no evidence was found that the moth had spread beyond the five boroughs.
  3. 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 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.
  4. Health advice is to stay away from oak trees known to contain oak processionary caterpillars or their nests, and to consult a GP or NHS 24 about any unexplained skin or irritation to the skin, throat or eyes, particularly during spring and summer. The caterpillars and their nests are always dangerous to approach because of the presence of toxic hairs, which can remain present and harmful in old nests for some years. However, the peak danger period for human health is from mid-May to the end of July. Because of the health risk the public should not try to deal with the caterpillars or their nests themselves. Contact details for local pest control operators qualified and equipped to deal with the species are available from local councils. 
  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.
  6. The caterpillars do not necessarily kill trees, which usually recover from attacks, 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. The species will attack other broadleaved trees such as hornbeam, hazel, beech, sweet chestnut and birch, but usually where they are close to severely defoliated oaks where their preferred food of oak leaves is limited.
  7. 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.


  • Forestry Commission / Forest Research - Charlton Clark, 0131 314 6500;
  • Ealing Council – Claire Parker, 020 8825 6551;
  • Richmond upon Thames Council - Pete Leriche, 020 8891 7160;
  • Brent Council – Martin Gavin, 020 8937 1067;
  • 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 – Frances Therrien, 0300 061 2128.