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NEWS RELEASE No: 1659617 JUNE 2016

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

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Nests made by caterpillars of Oak processionary moth around base of oak tree

People in parts of London, Surrey and Berkshire are being reminded not to touch the nests which oak processionary caterpillars could now 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.

Oak processionary moth (OPM) caterpillars and their nests are a tree, human and animal health hazard. The caterpillars shed thousands of their tiny hairs in the nests, and these can cause itching skin rashes and eye irritations and, more rarely, breathing difficulties in people and animals. The caterpillars are 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 build their distinctive white, silken, webbing nests and trails in June on the trunks and branches of oak trees, anywhere between ground level and many metres high. The nests become discoloured after several days, and harder to see as a result. They can also fall out of trees, creating a hazard to curious children and pets, and grazing livestock.

Alison Field, the Forestry Commission’s South-East England Director, 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, parks and gardens safe for everyone to enjoy, and the public can help us by reporting OPM nests and caterpillars to us so that they can be properly removed.

“However, please don’t try to remove the nests yourself. 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 nests or the caterpillars because of the health risks, but to see a pharmacist for relief from milder skin or eye irritations if they do come into contact. Consult a GP or NHS111 for more-serious reactions, and contact a vet if pets are badly 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. A map showing where OPM is known to be present is available at
  2. The affected areas are divided into ‘Core’, ‘Control' and 'Protected' zones for management purposes. Areas around the outer boundaries of the outbreak areas form the Control and Protected Zone, where the Forestry Commission is undertaking control on private properties to prevent or minimise spread of the pest into new areas, funded by the Department for the Environment, Food & Rural Affairs (Defra). Control in the core zone is at property owners’ discretion and expense. Maps of the zones are available in the OPM manual at
  3. The caterpillars begin emerging from eggs in oak trees in March or 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 caterpillars emerge the following spring.
  4. 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.
  5. OPM (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. OPM is native to southern Europe, where predators and local environmental factors keep its numbers in check. It was most likely accidentally introduced to Britain as over-wintering eggs previously laid on semi-mature oak trees imported for planting schemes. It has become established as far north as The Netherlands and northern Germany in recent years, aided by the movement of live plants in trade.
  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 - Charlton Clark, 0300 067 5049;
  • Public Health England - Cian Daly, 020 7811 7242.