People in parts of London, northern Surrey, West Berkshire and South Buckinghamshire are being reminded to look out for and report caterpillars of the oak processionary moth (OPM), which could be damaging oak trees in the area.

They are also advised to keep away from the caterpillars and their nests, because their hairs can cause itching skin rashes and other health problems, and to report sightings to the Forestry Commission.

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

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 on and under oak trees. The greatest risk period is May to July, when the caterpillars are active, although nests should not be touched at any time.

The Forestry Commission, councils and land managers are tackling the pest with a carefully controlled programme of oak tree treatment and nest removal. Alison Field, the Commission’s South-East England Director, said the public could play an important role in helping to control the pest by reporting sightings.

“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,” Ms Field 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 pest control experts.”

Dr Deborah Turbitt, London Deputy Director of Health Protection for Public Health England, 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 and livestock 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 more seriously 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 treatment.”

Infested oak trees should be treated by qualified operators under strict controls to ensure it is safe for people, pets, livestock and the environment.

• Report OPM sightings to the Forestry Commission, preferably with its Tree Alert on-line form available from www.forestry.gov.uk/opm1. Anyone who cannot use Tree Alert may email or telephone reports to ku.vo1732274969g.isg1732274969.yrts1732274969erof@1732274969mpo1732274969 or 0300 067 4442.

• Health advice is available from the “Insects that bite or sting” area of the NHS Choices website, www.nhs.uk/livewell.

• Anyone pruning or felling oak trees in the affected areas should contact Forestry Commission England’s Tree Health Unit beforehand on ku.vo1732274969g.isg1732274969.yrts1732274969erof@1732274969mpo1732274969 or 0300 067 4442 for advice about safe removal of the material.

• Further information is available from www.forestry.gov.uk/opm1.