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2. Health Advice - OPM manual

Your first duty as an oak tree owner or manager in the affected areas is to protect yourself and others, and pets and livestock, from the health risks which OPM poses.

The larvae develop tiny, irritating hairs from their third (L3) stage onwards to pupation. A single, fully grown larva can carry thousands of hairs. These hairs, which are barbed, contain an irritating substance called thaumetopoein, from which the species gets part of its scientific name, Thaumetopoea processionea.

Contact with the hairs can cause itching skin rashes and, less commonly, sore throats, breathing difficulties and eye problems. This can happen if people or animals touch the caterpillars or their nests, or if the hairs are blown into contact by the wind. The greatest risk period is May to July, but they can be present on old nests, and could be blown or touched at any time of year.

Some simple precautions will help to minimise the risk:


  • touch or go near nests or caterpillars
  • let children touch or go near nests or caterpillars
  • let animals touch or go near nests or caterpillars
  • try to remove nests or caterpillars yourself. (See Section 7: Nest and larvae removal.)


  • teach children not to touch or go near OPM nests or caterpillars;
  • train or restrain pets from touching or going near nests or caterpillars
  • see a pharmacist for relief from skin or eye irritations after possible OPM contact
  • call NHS111 or see your GP if you think you or someone you care for has had a serious allergic reaction
  • speak to a vet if you think your pet or livestock has been affected;
  • call in a suitably qualified pest control expert to remove infestations in your trees
  • warn any neighbours who have oak trees that they might also have an OPM infestation

Further advice is available from the NHS Choices website.

People working on or close to oak trees in the affected areas need stronger protective measures, including personal protective equipment (PPE). See Section 7: Nest and larvae removal.

 Skin rash caused by contact with hairs of oak processionary moth caterpillar

Skin rash caused by contact with OPM caterpillar hairs.





Last updated: 20th October 2016