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NEWS RELEASE No: 1649812 MAY 2015

London and Surrey people reminded about caterpillar pest in oak trees

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Procession of oak processionary moth (Thaumetopoea processionae) larvae on trunk of oak tree

People in parts of London and Surrey are being reminded not to approach caterpillars of the oak processionary moth (OPM), which are now emerging in oak trees in these areas.

They are also advised to keep children and animals away from the caterpillars and their nests, because the caterpillars’ hairs can cause itching skin rashes and other health problems. The public is also urged to report any sightings.

Affected areas include: several boroughs in West and South-West London; Bromley and Croydon and southern parts of Lewisham in South London; and Elmbridge and Spelthorne Districts in Surrey.

OPM caterpillars are a tree pest which was accidentally introduced to Britain. They feed on oak leaves, and in large numbers they can severely defoliate trees and leave them vulnerable to other pests and diseases.

Their tiny hairs contain a protein which can cause itchy skin rashes and, less frequently, eye and throat irritations and breathing difficulties in people and animals. The hairs can be blown on the wind, and left in their nests in and under oak trees. The greatest risk period is May to July, although nests should not be approached at any time.

The Forestry Commission, councils and land managers are tackling the pest with a carefully controlled programme of tree treatment and nest removal. Ian Gambles, the Forestry Commission's Director England,
said the public could play an important role in helping to control the pest by reporting sightings, but advised caution.

“We need reports of the caterpillars or their nests from the public or others, such as gardeners, tree surgeons and ground-care workers, who work or relax near oak trees,” he said.

“However, they should not try to remove the caterpillars or nests themselves. This needs to be carefully timed to be effective, and is most safely done by specially trained and equipped operators.”

Mr Gambles explained that extra surveying last year had revealed a greater outbreak area than was previously known, so the Commission had had to focus its control effort on the outer boundaries of the outbreak areas to limit spread of the pest and protect unaffected areas. He added:

“We are therefore encouraging oak tree owners and local authorities to continue helping to minimise the population and impacts in the core areas by finding and removing infestations.

“Many of them have given us strong support for several years, but we have produced on-line guidance to help those who are dealing with this pest for the first time.”

Dr Deborah Turbitt, Deputy Regional Director for Health Protection, London, endorsed the ‘don’t touch’ advice, saying:

“We strongly advise people not to touch or approach the caterpillars or their nests because of the health risks posed by the hairs. Pets can also be affected, and should be kept away as well. The Forestry Commission website has pictures to help identify the pest.

“See a pharmacist for relief from milder skin or eye irritations following possible OPM contact, or consult a GP or NHS111 for more-serious reactions. Contact a vet if animals are affected.

“We have issued advice to local GPs and health professionals to help them identify when patients have been affected by the caterpillars and to advise them on appropriate treatment.”

Trees are treated by fully qualified operators under strict health, safety and environmental controls to ensure it is safe for people and animals.

  • Sightings must be reported to the Forestry Commission, preferably with its Tree Alert on-line form available from
  • Maps of the ‘core’ and ‘control’ areas are available in the oak tree owners’ manual at .
  • Health advice is available from the “Insects that bite or sting” area of the NHS Choices website,
  • Working on oak trees – Anyone having oak trees pruned or felled in the affected areas must contact the Forestry Commission’s Plant Health Service beforehand on or 0300 067 5155 for advice about safe removal of the material.

Further information is available from

Notes to editor:

  1. Picture courtesy of Henry Kuppen.
  2. The London/Surrey outbreaks affect, or could affect, the following council areas: Barnet, Brent, Bromley, Camden, City of London, City of Westminster, Croydon, Ealing, Elmbridge, Epsom & Ewell, Haringey, Hammersmith & Fulham, Harrow, Hillingdon, Hounslow,  Kensington & Chelsea, Kingston Upon Thames, Lambeth, Lewisham, Merton, Richmond Upon Thames, Southwark, Spelthorne, Sutton and Wandsworth. An outbreak map is available at
  3. 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. Clear photographs are welcome. OPM lives almost exclusively in oak trees.
  4. It is hoped that the smaller Bromley/Croydon outbreak can be eradicated. However, it has not proved possible to eradicate the West and South-West London outbreak. The objective there is to slow or prevent its spread, and keep the population and impact as low as possible.
  5. The best times to tackle the pest are in the spring, by treating oak trees with insecticide after the caterpillars have hatched, and in the summer by removing their silken webbing nests from the trunks and branches of oak trees. (They do not make nests among the leaves). These are typically dome- or teardrop-shaped, about the size of a tennis ball or larger, and white when fresh, becoming discoloured over time.
  6. The products used to treat infested trees are safe for people, animals and the environment when used correctly. They are licensed for use by the Chemical Regulations Directorate, and are applied by trained operators who are fully compliant with all the relevant and very strict health and safety and environmental protection requirements.
  7. OPM (scientific name Thaumetopoea processionea) gets its name from the caterpillars' habit of moving about in nose-to-tail processions. It gets the first part of its scientific name from thaumetopoein, the irritating protein in the caterpillars’ hairs.
  8. A native of southern Europe, OPM has become established as far north as The Netherlands in recent years. It most likely entered Britain as eggs laid on young oak trees before they were imported from mainland Europe for planting. The moths lay their eggs in oak trees in July and August, and the caterpillars emerge from the eggs the following spring. The caterpillars feed in groups, and congregate in their nests at other times. The caterpillars pupate in their nests in June and July and emerge as moths up to four weeks later.
  9. OPM will attack other trees such as hornbeam, hazel, beech, sweet chestnut and birch, but usually only when it is short of oak leaves.
  10. This press release was amended on 28 July 2015 to add a picture credit.


  • Forestry Commission - Charlton Clark, 0300 067 5049;
  • Public Health England - Cian Daly, 020 7811 7242;
  • Royal Botanic Gardens, Kew - Bronwyn Friedlander or Tarryn Barrowman, 020 8332 5607,;
  • The Royal Parks – Sharon Donovan, 0300 061 2138;; and
  • the press offices of the local authorities in Note 1 above.