Oak Processionary Moth

Oak Processionary Moth - The Blue Tree Company

Whilst recently tree surveying at an education centre in the region, I came across a rather peculiar occurrence on one of their majestic mature oak trees. A swathe of undulating fur travelling up the main stem of the tree. Upon closer inspection, I noticed they were actually individual caterpillars, slowly marching as a tight-knit army. This could only mean one thing: Oak Processionary Moth and I knew I need to keep well away!

What is the Oak Processionary Moth?

The Oak Processionary Moth (OPM) is thought to have been accidentally introduced in 2005 on imported trees from continental Europe. They are almost exclusively found on the main stems and limbs of Oak trees. Oak trees are easily identified by their distinctive leaves and acorns.

These furry little fiends feast upon the oak leaves in large quantities and heavy infestations can completely defoliate the trees, leaving them weak and vulnerable. Stripping the trees bare of leaves is not the only problem – the hairs are the caterpillars main defence mechanism and coming into contact with them can cause skin and eye irritations, sore throats and breathing difficulties in people and animals.

The core zone of infestation centres around London, and is spreading out to neighbouring regions.

How to identify their nests

Their nests look like silken sacks that may more commonly be associated with spiders, and range in size from a golf ball to a rugby ball. These nests can be found on the main trunk and underside of structural limbs, where-as the caterpillar itself will be found travelling in convoy (hence the name processionary) to the leaves or within the leaf canopy. There can be many nests within one tree. These must be avoided as hairs from the caterpillars become trapped in the silk. It is also important to note that the nests can be very low down, near the ground so can be problematic for children and pets. Nests must be removed by trained professionals using specialist equipment, to ensure the safety of all concerned.

What can I do?

The Forestry Commission recommends the following health precautions:


• touch or go near to the nests or caterpillars;
• let children touch or go near to nests or caterpillars;
• let animals touch or go near to nests or caterpillars;
• attempt to remove the nests or caterpillars yourself.


• teach children not to touch or approach the nests or caterpillars;
• be vigilant and train or restrain pets from touching or approaching them;
• keep horses and livestock a safe distance from infested oak trees. If needed, covering or stabling livestock can help;
• visit a pharmacist for relief from skin or eye irritations if you suspect OPM contact;
• call NHS111 or visit a doctor if you suspect you or someone in your care has had a serious allergic reaction;
• speak to a vet if you think your pet or livestock is affected;
• contact an expert to remove infestations in your own trees;
• report any sightings to The Forestry Commission

If you suspect you have seen some OPM, ensure you follow the precautions above or for further help and advice, please contact Alan at The Blue Tree Company. Call 01462 450203 or email info@thebluetreecompany.com

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