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NEWS RELEASE No: 166764 JULY 2017

Reminder to report signs of threat to local oak trees

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Cluster of Oak processionary moth (Thaumetopoea processionea) larvae feeding on oak leaves

People in parts of London and the South East 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.

OPM is an invasive tree pest and feeds almost exclusively on oak leaves. In large numbers they can strip trees bare and leave them vulnerable to other pests, diseases and drought. The public are being urged to report any sightings to the Forestry Commission, who will safely remove the caterpillars and nests.

The Forestry Commission are working closely with councils and land managers in affected areas to tackle the pest and protect oak trees, through a carefully controlled programme of tree treatment and nest removal.

Alison Field, the Commission’s South East England Director said the public can play an important role in helping to control the pest by reporting sightings, saying;

 “We are working hard to protect our oak trees from the devastating effects that large numbers of these caterpillars can cause. To help us to do this, we are asking anyone who spots the caterpillars or their nests to contact the Forestry Commission.”

“However it’s vital that members of the public avoid any contact with the caterpillars or the nests. The treatment of infested oak trees needs to be carried out by specially trained experts and treatment must be carefully timed in order for it to be most effective.”

Infested oak trees should be only be treated by qualified operators under strict controls to ensure it is safe for people, pets, livestock and the environment. Hairs from the caterpillars can cause itching skin rashes and other health problems, so it is important to avoid all contact with the caterpillars and their nests. Anyone who does come into contact with the hairs should seek advice from a pharmacist. If your pet is affected, you should seek assistance from a vet.

The reports that the Forestry Commission have received to date have helped to build a better picture of OPM distribution and has meant that further control measures can be taken.


How to identify OPM


OPM caterpillars;

  • move about in nose-to-tail processions;
  • often form arrow-headed processions, with one leader and subsequent rows containing several caterpillars abreast;
  • are most likely to be found in oak trees;
  • are most likely to be seen in summer;
  • have very long, white hairs which contrast markedly with other, shorter hairs; and
  • do not live on fences, walls and similar structures, as some caterpillar species do.


OPM nests;

  • are usually roughly semi-spherical or teardrop-like in shape before they begin to collapse, when they can become bag-like;
  • occur almost exclusively on oak trees;
  • are almost always attached to the trunks or branches of oak trees; and
  • are almost never woven among the leaves. Silken webbing nests among oak leaves, or in other trees and shrubs and on other structures, are almost certainly NOT made by OPM and need NOT be reported.

If you spot any caterpillars or nests affecting oak trees in your area you can submit a Tree Alert here. Alternatively contact the Forestry Commission on or call 0300 067 4442. 



Media contact: Megan Phillips on 0300 067 4084 or email


Notes to Editor

  1. The Forestry Commission is the government department responsible in England for protecting, expanding and promoting the sustainable management of woods and forests and increasing their value to society and the environment.
  2. To date, OPM outbreaks have been confirmed in London, northern Surrey, West Berkshire, south Hertfordshire and south Essex.  A distribution map showing confirmed outbreaks of breeding of OPM is available at
  3. OPM is tackled in the spring by treating oak trees with insecticide after the caterpillars have hatched and in the summer by removing their nests from trunks and branches of oak trees.
  4. The products used to treat infested trees are licensed by the Chemical Regulations Directorate and are safe for people, pets and livestock and the environment.  They are used by trained operators who are fully compliant with all the relevant health, safety and environmental protection requirements.
  5. OPM is a native of southern Europe but has become established as far north as the Netherlands in recent years. It most likely entered Britain as eggs laid on young oak trees before they were imported from mainland Europe for planting.
  6. The moths lay their eggs in oak trees in July and August and the caterpillars emerge the following spring. They feed in groups and congregate in their nests at other times.
  7. OPM will attack other trees such as hornbeam, hazel, beech, sweet chestnut and birch but usually only when it is short of oak leaves.