They are also being asked to report any sightings.
The caterpillars are a forestry pest and can be a health hazard. They damage oak trees by feeding on the leaves, and their tiny hairs contain a toxin that can cause itchy skin rashes as well as eye and throat irritations.
Forestry, health and local authorities are dealing with outbreaks of the moth in five boroughs of West London and in Pangbourne, near Reading in West Berkshire.
Since the species was first found in Pangbourne in 2010 the Forestry Commission and West Berkshire Council have begun efforts to eradicate it from the area before it can spread further, as well as to protect local people from the health risks.
It has also become established in the London Boroughs of Ealing, Brent, Hounslow, Richmond upon Thames and Hammersmith & Fulham, since it was found there in 2006. Eradication from this area is now considered impractical, so the Forestry Commission's policy is to work to contain it within those boroughs. The Commission is therefore surveying a 10-kilometre (6-mile) buffer zone around the infested area, and will require the removal of any caterpillars or nests in the buffer zone.Control within the infested area is the responsibility of tree owners and local authorities.
Stewart Snape, deputy head of the Forestry Commission's Plant Health Service, said the public could help, although he urged people not to touch the caterpillars or their nests.
"We welcome reports of caterpillars or their nests from the public or others, such as gardeners and tree surgeons, who are out and about in areas with oak trees," he said.
"However, the public should not try to remove the caterpillars or nests themselves. These jobs need to be carefully timed to be most effective, and are best done by specially trained and equipped operators."
Dr Brian McCloskey, director of the Health Protection Agency in London, endorsed this advice for health reasons, saying:
"We strongly advise people not to touch or approach the caterpillars or their nests because of the health risks caused by the toxin-containing hairs. Pets can also be affected and should be kept away as well.
"Anyone who experiences an itchy skin rash or other allergic symptoms after being near oak trees in these areas should consult their GP."
Snape also asked people who were having oak trees pruned or felled in either of the affected areas to contact the Forestry Commission's Plant Health Service beforehand on email@example.com or 0131
314 6414 for advice about safe removal of the material.
Sighting reports should include a precise description of the location.
An Ordnance Survey grid reference is ideal, otherwise an accurate postal address with the full postcode, and/or a clear description of the tree's exact position, is helpful. Digital photographs may also be sent as an aid to identification.
Sighting reports - can be sent to Forest Research, part of the Forestry Commission, on 01420 22255 or firstname.lastname@example.org, or to the local council.
Health advice - Anyone who is worried by an intensely itchy or painful skin rash, sore throat and irritated eyes, and who might have been near oak trees harbouring OPM, should consult their GP or call NHS Direct on
0845 4647. Health information is also available from www.hpa.org.uk.
Pest control - A list of local pest control operators qualified to deal with OPM is available from the Forestry Commission on 0131 314 6414 / email@example.com, or the local Council.
Further information is available from