Walkers have been advised to be on the lookout for pest caterpillars that can damage oak trees and cause skin rashes and breathing difficulties.

The Forestry Commission has named several areas across London, Surrey, Berkshire and Buckinghamshire where trees are at risk from caterpillars of the oak processionary moth (OPM).

Surrey Comet:

A cluster of oak processionary moth. Pic credit: Forestry Commission

Residents are advised to keep away from the caterpillars and their nests and to report sightings to the Forestry Commission.

The government department warns that OPM’s tiny hairs can cause itchy skin rashes and, less frequently, eye and throat irritations and breathing difficulties in people and animals.

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

Surrey Comet:

An oak processionary moth nest. Pic credit: Ralph Parks

Alison Field, the Commission's south east England director, said the public should report any suspected OPM sightings.

She said: “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.

“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.”

Surrey Comet:

An oak processionary moth procession on a tree truck. Pic credit: Henry Kuppen

Dr Deborah Turbitt, London deputy director of health protection for Public Health England, advised anyone who comes into contact with OPM to visit a pharmacist, consult an GP, or dial 111 for more serious reactions. She advises pet-owners to contact a vet if animals are affected.

Dr Turbitt said: “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.

“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.”

Surrey Comet:

An oak processionary moth procession on a tree trunk. Pic credit: Henry Kuppen

To report OPM sightings, visit www.forestry.gov.uk/opm1, call 0300 067 4442, or email opm@forestry.gsi.gov.uk

For health advice, see the ‘insects that bite or sting’ area of the NHS Choices website at www.nhs.uk/livewell