Oak processionary caterpillars - the larval form of the moth - threaten Britain's oak trees, some of which are already under stress from other factors. They do this by eating the leaves, which can lead to complete loss of foliage.
In addition, the caterpillars' hairs contain a toxin that can cause painful and sometimes serious symptoms in people and animals, and for this reason the public are advised not to touch the caterpillars or their nests, and to keep pets away from them.
The caterpillars are now hatching from eggs laid on oak trees last autumn. The Forestry Commission and its local partners want the public to help by reporting sightings of the caterpillars or the silken nests they spin on the branches and trunks of infested trees to one of the organisations listed below. Caterpillars and nests can then be treated and removed by suitably equipped and trained professionals.
Oak processionary moth (Thaumetopoea processionea) - a native of southern and central Europe - turned up on trees in west and south-west London in 2006, and began breeding in oak trees in a number of locations there, including Kew Gardens.
The Forestry Commission, working with Ealing, Richmond upon Thames, Brent and Hounslow Councils, Defra, the Royal Botanic Gardens Kew, and the Health Protection Agency London, launched an action plan last year to monitor and eliminate caterpillar populations before the infestation spreads out of London and becomes permanently established in Britain.
Armed with survey information and reports of sightings from the public and others, teams with special training and equipment - including protective suits - destroyed more than 700 nests last year. Many were destroyed during the period when the caterpillars developed into pupae in the nests from late June, before re-emerging as adult moths in August. However, subsequent pheromone trapping of male moths in the late summer indicated that not all the nests had been destroyed, and it is likely that some of the adults will have succeeded in laying eggs.
Roddie Burgess, head of the Forestry Commission's plant health service, said,
"We expected that we would not find and destroy every last nest and caterpillar last year, but we believe that we greatly reduced the potential breeding population. We therefore think we still have a good chance of getting rid of this pest while it is confined to this part of London and before it spreads any further, so we're going after the remaining ones this spring.
"If it's allowed to get established it will be a problem not only to Britain's much-loved oak trees - and possibly other trees that it can also attack - but also to human health.
"It does not necessarily kill trees - they usually recover - but it would add another, unwelcome stress to Britain's oaks, which in some areas are already suffering from conditions such as oak decline and drought. So from woodland owners' point of view, it makes sense to try to contain or, ideally, eradicate it while we still can."
In a joint statement, Councillor Martin Elengorm, Cabinet member for environment at Richmond upon Thames Council, Chris Begley, emergency planning co-ordinator for Ealing Council, Councillor Irwin Van Colle, lead member for environment at Brent Council, and Councillor Barbara Reid, executive member for environment and planning at Hounslow Council, said,
"We have a good picture of where the infested trees are, but we're still keen for the public to report any sightings of the caterpillars or their nests to us or to Forest Research (the research agency of the Forestry Commission). The more of them we know about, the better our chances of success.
"We would stress, however, that people should not try to deal with the nests or caterpillars themselves. Even old, disused nests can be hazardous, because they can be packed with the caterpillars' hairs and shed skin, so this is a specialist task needing properly equipped and trained people to ensure that it is done as effectively and safely as possible.
"People should also keep their pets away from nests and caterpillars, because animals can be affected in the same ways."
Dr Roger Gross, regional director of the Health Protection Agency London, added,
"If it becomes established here, as it has in other European countries, a lot of people might get a very itchy skin rash, and a few will get more-troublesome symptoms such as itchy eyes and breathing problems.
"If it does become an on-going problem here, we would have to advise people to avoid affected oak trees during the peak months. So we welcome the work of the Forestry Commission and the local authorities to try to eradicate this threat, and we are working closely with them.
"Advice is being issued to local GPs and other health professionals to help them to identify when patients have been affected by the caterpillars' hairs, and to advise them about appropriate treatment.
"Anyone with a severe reaction, or who is uncertain what has caused their rash, should consult their GP."
The combination of the caterpillars' sharp, barbed hairs and their associated toxin can cause irritation and allergic reactions in people and animals. Contact most commonly causes intensely itchy or painful skin rashes, but also sore throats, eye problems and breathing difficulties. These can happen because people touch the caterpillars or their nests, and because the wind can blow the hairs into contact with people.
Apart from the continuing danger from nests, the peak danger period for human health is during the caterpillars' final two stages of development, usually in late May and through June, when they are covered with thousands of the microscopic, irritating hairs.
The caterpillars then pupate within the nests in late June and early July and emerge as adult moths between one and two weeks later. The moths lay their eggs in oak trees in July and August, and the eggs hatch caterpillars the following spring. They start feeding on young leaves as soon as they hatch, and this is the best time to use active control measures, which is why this year's action plan is being launched now.
The caterpillars feed together in groups and, when not feeding, they congregate in communal nests made of matted, white silk webbing. The nests are typically about the size of a tennis ball, but can be larger, especially if the population builds up. The species gets its common name from the caterpillars' habit of moving about in the trees or on the ground in long, nose-to-tail processions.
Anyone who thinks they have found oak processionary caterpillars, or their nests, should report their sightings to Forest Research or Ealing, Richmond upon Thames, Brent or Hounslow Council, giving as precise details as possible about 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 photos sent with emailed sighting reports can help experts to confirm the sighting.
Sightings anywhere can be reported to Forest Research by telephoning 01420 22255 or by e-mail to christine.tilbury@forestry.gsi.gov.uk. Otherwise, they can be reported to the relevant Council as follows:
Further information, including pictures and a "tree pest advisory note", is available on Forest Research's website, www.forestresearch.gov.uk/oakprocessionarymoth , and the Forestry Commission's website at www.forestry.gov.uk/planthealth . Further health information is available from NHS Direct, 0845 4647, www.nhsdirect.nhs.uk.
NOTES TO EDITOR:
- An emergency measure to protect Great Britain against further introductions of oak processionary moth came into force on the 31st March 2008. It takes the form of an amendment to the Plant Health (Forestry) Order 2005, and requires that all oak trees imported from European Union (EU) Member States are accompanied by a "plant passport". The plant passports will confirm that the trees have been grown in a nursery and that they come from an area where the place of production and its immediate vicinity have been free from oak processionary moth since at least the beginning of the last cycle of vegetation. The Forestry Commission has also asked the European Commission to draft measures to protect against further introductions, and this is likely to result in the designation of Great Britain, at least, as a "protected zone". However, because it is likely to be some time before the new EU measures can be adopted, Britain's Forestry Ministers agreed to put the amendment to the Plant Health Order in place as quickly as possible to prevent further infested oak trees entering Great Britain in the meantime.
- Oak processionary moth is a native of central southern Europe, although active infestations of caterpillars have been found further north, including northern France, Belgium and The Netherlands, over the past 15-20 years. It is most likely to have entered Britain as over-wintering eggs on trees imported for planting here.
- It is possible that climate change has been a factor in the expansion of its range. Milder winters and, in particular, fewer and less-severe late spring frosts which could kill significant numbers of emerging caterpillars, might have improved its chances of survival in more northern latitudes.
- The species will attack other broadleaved trees as well as oaks, such as hornbeam, hazel, beech, sweet chestnut and birch, although usually only where these exist close to severely defoliated oak trees where the preferred food supply (oak leaves) is limited.
- The moths' populations can be very cyclic, so that a severe infestation one year can be followed by a population collapse for a number of years before the population builds up again. This has been observed in The Netherlands, where the population was very high in 1996, 2001 and 2007, but significantly lower between those years.
NEWS MEDIA CONTACTS:
- Forestry Commission / Forest Research - Charlton Clark, 0131 314 6500 or 07810 181067;
- Ealing Council - Verity Adams, 020 8825 5462;
- Richmond upon Thames Council - Cristian Marcucci, 020 8487 5049;
- Brent Council - Michelle Hyland, 020 8937 5321, ext 1066;
- Hounslow Council - Jini Amarasekara, 020 8583 2186;
- Health Protection Agency London - Claire Kennedy, or Emily Collins, 020 7759 2824 / 34;
- Kew Gardens - Anna Quenby Bronwyn Friedlander or Catherine Owen, 020 8332 5607.