Borough Insight

Oak processionary moth

The caterpillars of the oak processionary moth can affect the health of people and animals (and oak trees).

This invasive species has been identified at sites in Epsom & Ewell in the last couple of years.OPM trunk

A protein in the caterpillars' tiny hairs can cause skin and eye irritations, sore throats and breathing difficulties in people and animals who come into contact with them. The caterpillars can shed the hairs as a defence mechanism, and lots of hairs are left in the nests, which is why nests should not be touched without protective clothing.

Do not:

  • touch or approach nests or caterpillars
  • let children touch or approach nests or caterpillars
  • let animals touch or approach nests or caterpillars
  • try removing nests or caterpillars yourself.

You should see a pharmacist for relief from skin or eye irritations after a suspected contact or call NHS111 or see a doctor if you think you or someone in your care has had a serious allergic reaction. You should consult a vet
if you think your pet has been seriously affected.

OPM nestThe species derives its common name from the fact that the caterpillars move about in nose-to-tail processions and live primarily on oak trees. The caterpillars feed on oak leaves, and large populations can strip trees bare, leaving them weakened and vulnerable to other threats.

The moth is a native of southern Europe, where predators and environmental factors usually keep its numbers in check and minimise its impact. the moth was first accidentally introduced to Britain in 2005, almost certainly as eggs which had been laid on live oak plants imported from continental Europe. 

The images show (top) a typical procession and (bottom) nests wrapped in their protecting cocoon webbing on the base of on an oak tree.

For further information, including your responsibilities if you have an infected oak tree on your land, see the Forestry Commission website.


Images: caterpillars procession on trunk Copyright H Kuppen, nests on trunk Crown Copyright. Used with permission.


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