Oak processionary moth caterpillars (OPM), a pest species which are a hazard to tree, human and animal health, have been found in the West Wickham area of Bromley in south-east London.
The Forestry Commission believes it is a separate outbreak rather than an extension of the known outbreak in west London.
A group of infested oak trees in an area with public access were reported to the Forestry Commission on Wednesday 4 July by Bromley Borough Council. The area was immediately cordoned off to protect the public from the caterpillars' toxic hairs, and the council called in pest control operators to remove the caterpillars and their silken webbing nests.
Other oak trees in the area are now being surveyed.
OPM caterpillars - the larval stage of the moths' lifecycle - are a threat to oak trees because they eat oak leaves, and in severe cases can defoliate whole trees, leaving them vulnerable to other threats.
Alison Field, South East England regional director of the Forestry Commission, said: "It's extremely disappointing that OPM has been found in this part of London so far from the existing outbreak in west London, where they have become established since being accidentally introduced from Continental Europe about 2005.
"The distance away from the west London outbreak suggests this is a separate outbreak, although we will be investigating the pathway by which it got to Bromley.
"We are working with Bromley Council and others involved to eradicate the outbreak as quickly as possible. The location is close to the boundary with Croydon Borough, and we have alerted Croydon Borough Council."
Local people are urged not to touch the nests or caterpillars or try to remove them.
Alison Feild continued: "At this time of year the caterpillars build white, silken webbing nests in oak trees in preparation for pupating into adult moths. Tree owners should not try to remove nests themselves, because they can be full of the caterpillars' toxic hairs. To be as effective and safe as possible this job needs to be done by specially trained and equipped operators, and the nests must be disposed of properly."
Sightings of caterpillars or nests can be reported to the Forestry Commission's Forest Research agency on 01420 22255; email: christine.tilbury@forestry.gsi.gov.uk; or to Bromley Council's tree team on 0208 313 4471, or to the local Council.
People who are having oak trees pruned or felled in affected areas must contact the Forestry Commission's Plant Health Service beforehand on plant.health@forestry.gsi.gov.uk or 0131 314 6414 for advice about safe removal of the material. The Plant Health Service and local councils in outbreak areas can also supply details of suitably qualified pest control operators who can remove infestations.
Contact with the hairs can cause itchy skin rashes, itchy eyes and a sore throat. Anyone suspecting they have been exposed to the caterpillars and have these symptoms should contact their GP, or NHS Direct on 0845 4647, advising them of the possible contact with OPM hairs. Health information is available from the HPA website, www.hpa.org.uk.
About the Oak Processionary Moth
OPM is a native of southern Europe which has become established as far north as The Netherlands over the past 20 years. It has been found in Brent, Ealing, Hounslow, Richmond upon Thames, Hammersmith & Fulham, Merton and Wandsworth Boroughs since it was first found in west London in 2006.
A separate outbreak is subject to eradication action in Pangbourne, West Berkshire. Both earlier outbreaks are believed to have originated from young trees infested with OPM eggs imported from continental Europe for landscaping projects. The Forestry Commission hopes the Pangbourne outbreak, which is still small, can be eradicated.
However, it has not proved possible to eradicate the West London outbreak, and the objective there is to slow or prevent its spread, and keep its population as low as possible.
The species gets its name from the caterpillars' habit of moving about in nose-to-tail processions. Its scientific name (Thaumetopoea processionea) reflects thaumetopoein, the toxin in the hairs.
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 be sent to aid identification.
The best times to tackle the pest are in the spring, with insecticide after the caterpillars have hatched, and in the summer by removing the distinctive white, silken nests where they congregate and pupate into adult moths. Nests are always dangerous to approach because of the presence of the caterpillars' toxic hairs. The peak danger period for human health is from mid-May to late July.
The caterpillars pupate in their nests in late June and early July and emerge as moths between one and four weeks later. The moths lay their eggs in oak trees in July and August, and the eggs hatch caterpillars the following spring. Before pupation, the caterpillars feed in groups, and at other times congregate in the nests, which are typically about the size of a tennis ball.
The caterpillars do not necessarily kill trees, which usually recover, but they can add another unwelcome stress to Britain's oak trees, which in some areas are already suffering from other stresses such as acute oak decline.
The species will attack other broadleaved trees such as hornbeam, hazel, beech, sweet chestnut and birch, but usually only when they run out of their preferred food of oak leaves.