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NEWS RELEASE No: 162764 JUNE 2014

‘Don’t touch’ reminder over oak processionary caterpillar nests in London, Surrey and Berkshire

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Nest of oak processionary moth (Thaumetopoea processionea) under construction, showing a single larva (caterpillar) laying down more silk as part of the construction process

People in parts of London, Surrey and Berkshire are being reminded not to touch the nests which oak processionary caterpillars could be building in oak trees in these areas.

They are also being advised to protect animals from contact with the nests, and to report sightings to the Forestry Commission or local Councils.

This is because the nests contain thousands of the caterpillars’ hairs, which contain an irritating substance which can cause unpleasant skin rashes and, sometimes, eye and throat irritations in people and animals. They are also a tree pest because they eat oak leaves: large numbers can strip oak trees bare, leaving them weakened and vulnerable to other threats.
The caterpillars are the larval stages of the pest oak processionary moth (OPM), and in June they build distinctive white, silken, webbing nests and trails on the trunks and branches of oak trees. The nests become discoloured after several days.

There are three separate outbreaks of the pest: one in several boroughs in West and South-West London and the Elmbridge and Spelthorne areas of Surrey; one in the Bromley/Croydon area of South London; and one in the Pangbourne district of West Berkshire. Each outbreak is thought to have begun with a separate accidental introduction as eggs on semi-mature oak trees imported from continental Europe. 

Ian Gambles, the Forestry Commission’s Director England, encouraged local people to help tackle the pest by reporting sightings of the nests and caterpillars, but not to touch or approach them:

“We want to keep our woods and parks safe for everyone to enjoy, and the public can help us by reporting OPM nests and caterpillars to us or their local council so that they can be properly removed.

“We also advise people against trying to remove the nests themselves, even if they own the oak tree. To be as effective and safe as possible, this job needs to be timed just right and done by people with the right training and equipment, and the nests must be disposed of properly."

Dr Deborah Turbitt, London Deputy Director of Health Protection for Public Health England, endorsed the ‘don’t touch’ message, adding:

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

“We advise people to 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 pets are affected.

“We have issued advice to local GPs and health professionals to help them identify when patients have been affected by contact with OPM hairs, and to advise them on appropriate treatment.”


  1. Affected areas - The London outbreaks of oak processionary moth affect, or could affect, oak trees in 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. The caterpillars begin emerging from eggs in oak trees in April. They build nests in June and congregate in them between feeding sessions. They then pupate in the nests in late June and early July to emerge as adult 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.
  3. The peak risk period for human and animal health is from mid-May to the end of July. However, nests should not be approached at any time, because the hairs can remain active for a long period.
  4. The Forestry Commission is working with local authorities and tree owners to eradicate or contain the pest under a Defra-funded programme. It is hoped that the smaller Pangbourne and Bromley/Croydon outbreaks can be eradicated, but we currently believe it will not be possible to eradicate the larger West and South-West London outbreak, so the objective there is to slow or prevent its spread, and keep its population as low as possible.
  5. Oak processionary moth (Thaumetopoea processionea) gets its name from the caterpillars' habit of moving about in nose-to-tail processions. It derives the first part of its scientific name from thaumetopoein, the irritating protein in its hairs.
  6. A native of southern and central Europe, OPM most likely entered Britain as over-wintering eggs previously laid on semi-mature oak trees imported for planting. The three outbreaks in Britain are thought to have begun with three separate accidental introductions as eggs laid on semi-mature trees imported from continental Europe. Although a native of southern Europe, where predators and local environmental factors keep its numbers in check, OPM has become established as far north as The Netherlands over the past 20 years, aided by the trade in live plants. Climate change might have been a factor: fewer late spring frosts and lower spring rainfall, which could kill emerging caterpillars, might have improved its chances of surviving in more northern latitudes.
  7. OPM will occasionally attack other broadleaved trees such as hornbeam, hazel, beech, sweet chestnut and birch, but usually only where these trees are close to oak trees which they have stripped of leaves so that they are short of their preferred food.


  • Forestry Commission / Forest Research - Charlton Clark, 0131 314 6500 or 07810 181067;
  • West Berkshire Council – Peta Stoddart-Crompton, 01635 519670;
  • Public Health England - Cian Daly, 020 7811 7242;;
  • Royal Botanic Gardens, Kew - Bronwyn Friedlander or Tarryn Barrowman, 020 8332 5607,;
  • The Royal Parks – Jessica Chambers, 0300 061 2128;; and
  • The press offices of the London local authorities named Note to Editor No. 1.