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Oak Processionary Moth caterpillar sightings confirmed


Thursday, 18 July, 2019

There have been several confirmed sightings of Oak Processionary Moth (OPM) caterpillars in parts of the borough and residents are being reminded to avoid all contact with this hazardous tree pest.

Oak Processionary Moths have been present in the UK since 2012 with infestations found in London and parts of the South East in recent years.

Their nests are typically dome or teardrop-shaped, ranging in size – from a ping pong ball to as large as a rucksack. They are white when fresh, but soon become discoloured and brown. The caterpillars have black heads and bodies covered in long white hairs that contain proteins which can cause itchy rashes, eye, and throat irritations. They can also occasionally cause breathing difficulties in people and pets, so should not be touched under any circumstances.

The greatest risk period is May to July when the caterpillars emerge and feed before pupating into adult moths, but nests, even old ones, should not be touched at any time. The caterpillars feed on oak leaves, which can leave the trees vulnerable to other pests and diseases and drought.

Cllr Kevin Davis, Portfolio Holder for the Environment, said: “Officers have found infestations on several council sites across the borough, which we are dealing with in the correct manner to minimise harm to the public. The likelihood of there being nests on private land is high, which is why we’re reminding residents what to look out for, and not to have any contact with them. All sightings of caterpillars and nests need to be reported to the Forestry Commission, which has a programme in place to tackle the pest.”

Do not touch or approach OPM nests or caterpillars and do not try removing nests or caterpillars yourself. All sightings need to be reported to the Forestry Commission:

You will need to give a precise location as to where the infestation was sighted and if possible, provide a photo.

What to look out for

  • OPM moths, the adult form of the species, are undistinctive brown moths similar to other species, and are difficult to accurately identify. They are not a health hazard and do not need to be reported unlike their junior forms.
  • OPM caterpillars have a distinctive habit of moving about in late spring and early summer in nose-to-tail processions, from which they derive their name. They live and feed almost exclusively on oak trees and can sometimes be seen processing across the ground between oak trees. They have very long, white hairs which contrast markedly with the much shorter, almost undetectable irritating hairs; have a grey body and dark head. Older larvae have a central dark stripe with paler lines down each side.
  • OPM nests are built in early summer; are made on the trunks and branches of oak trees; are made of distinctive, white, silken webbing, which are accompanied by white, silken trails on the trunks and branches of oak trees. These become discoloured after a short time, and more difficult to see as a result, as do the silken trails. Several nests can occur on the same tree or branch, anywhere from ground level to high in the oak tree.