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NEWS RELEASE No: 1592229 APRIL 2013

Alert over caterpillar pest in London and Berkshire

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Oak processionary caterpillars (Thaumetopoea processionea) on Quercus robur

People in parts of London and Berkshire are being reminded by the Forestry Commission, Public Health England and local authorities not to touch caterpillars of the oak processionary moth, which are beginning to emerge in oak trees in these locations.

They are also advised to keep children, pets and livestock away from the caterpillars and their nests, and to report any sightings.

The affected areas are several boroughs in West and South-West London, Bromley and Croydon in South London, and Pangbourne in West Berkshire.

Caterpillars of the oak processionary moth (OPM), which was accidentally introduced to Britain from mainland Europe in 2006, are a tree pest and pose a threat to human and animal health.

They are a tree pest because they damage oak trees by feeding on the leaves, in some cases leaving the trees severely defoliated and vulnerable to other pests, diseases or drought.

And they pose a risk to human and animal health because they have tiny, toxin-containing hairs which, on contact, can cause itchy skin rashes in people and animals. Eye and throat irritations have also been reported as symptoms. The hairs can be blown on the wind, and left in the silken, web-like nests which the caterpillars build in oak trees. They pose the greatest risk from May to July, although nests should not be approached at any time.

The Forestry Commission is working with local authorities and land managers to tackle the outbreaks with a carefully controlled programme of tree spraying and nest removal. Ian Gambles, Director of Forestry Commission England, said the public could help, but urged caution.

“We need, and welcome, reports 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,” he said.

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

Dr Yvonne Doyle, London Regional Director of Public Health England, endorsed this advice, saying:

“We strongly advise people not to touch or approach the caterpillars or their nests because of the health risks posed by the toxin-containing hairs. Pets can also be affected and should be kept away as well. If you would like to know what these caterpillars look like, please see the Forestry Commission’s website for pictures.

“Anyone who experiences an itchy or painful skin rash or a sore throat and irritated eyes after being near oak trees in these areas should consult their GP or NHS 111.

“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.”

Tree spraying is done by fully qualified operators under strict health, safety and environmental controls to ensure it is safe for humans and animals.

  • Sighting reports – can be sent to the local council, or to the Forestry Commission, using the Commission’s Tree Alert app or on-line form at
  • Health advice - Anyone who is worried by an intensely itchy or painful skin rash, sore throat or irritated eyes, and who might have been near oak trees infested with OPM, should consult their GP or NHS 111. Health information is also available from the Public Health England website ( under ‘Oak Processionary Moth’. Anyone concerned about their pets should contact a vet.
  • Pest control - A list of local operators who can deal with OPM is available from the Forestry Commission on 0131 314 6414 /, or the local Council.
  • 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 0131 314 6414 for advice about safe removal of the material.

Further information is available from

Notes to editor:

  1. The London outbreaks affect, or could affect, the following local authority areas: Barnet, Brent, Bromley, Camden, City of London, City of Westminster, Croydon, Ealing, Elmbridge, Epsom & Ewell, Haringey, Hammersmith & Fulham, Harrow, Hillingdon, Hounslow, Islington, Kensington & Chelsea, Kingston Upon Thames, Lambeth, Merton, Richmond Upon Thames, Southwark, Spelthorne, Sutton and Wandsworth.
  2. 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 are welcome as an aid to identification. OPM is most likely to be seen in or near oak trees.
  3. The Forestry Commission hopes that the smaller Pangbourne and Bromley/Croydon outbreaks 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.
  4. The best times to tackle the pest are in the spring, with insecticide after the caterpillars have hatched, and in the summer by removing the distinctive white, silken nests in which they congregate and pupate into adult moths. The products used to treat infested trees are safe for human and animal health and the environment when used correctly. They are licensed for use by the Chemical Regulations Directorate, and are applied by fully trained operators who are fully compliant with all the relevant and very strict health and safety and environmental protection requirements.
  5. 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 chemical in the caterpillars’ hairs.
  6. A native of southern Europe, OPM has become established as far north as The Netherlands over the past 20 years. It most likely entered Britain as eggs laid on young oak trees before they were imported from mainland Europe for planting here. The caterpillars pupate in their nests in late June and early July and emerge as moths up to four weeks later. 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 at other times congregate in nests of matted, white, silken webbing, which are typically about the size of a tennis ball.
  7. OPM will attack other trees such as hornbeam, hazel, beech, sweet chestnut and birch, but usually only where oaks are severely defoliated and its preferred food of oak leaves is limited.


  • Forestry Commission / Forest Research - Charlton Clark, 0131 314 6500;
  • West Berkshire Council – Arthur Cullen, 01635 519675;
  • Public Health England - Tycie West or Cian Daly, 020 7811 7243/7242;
  • Royal Botanic Gardens, Kew - Anna Quenby, Bronwyn Friedlander or Tarryn Barrowman, 020 8332 5607,;
  • The Royal Parks – Jessica Chambers, 0300 061 2128;;
  • The press offices of the London local authorities named in Note to Editor No 1.