Oak Processionary Moth [OPM] – Spraying and Nest Removal

Caterpillars in procession


Infestations of OPM caterpillars were first surveyed and monitored in Richmond upon Thames in 2006.  Since then the population has gradually expanded within South-East England. OPM is of a major concern for several reasons.  In the later stages of its caterpillar development, between late May and early June, the caterpillars are covered in minute hairs that contain a toxin.  If those hairs come into contact with skin, various persistent symptoms can occur.  This includes an itch rash, sore throats, conjunctivitis and respiratory problems.  These hairs collect in nests and are so tiny they can be blown about by the wind.

The female adult Oak Processionary Moth lays around 300 eggs in small strips or “plaques” usually in the canopy of a free-standing mature or semi-mature oak tree.  Detection at this stage is near impossible and even close up the 2-4cm long plaques are difficult to spot.  Not all the eggs will necessarily hatch in the same year.  Once hatched, the caterpillars pass through six instars [stages].

Stage 1: [April-May]  the freshly hatched caterpillars are 3mm long, red and have no toxic hairs.

Stage 2: [Early-mid May]  they have turned black but still lack hairs.

Stage 3: [Mid-late May] the caterpillars “process” down from the top of the tree and begin developing urticating hairs.

Stage 4: [Early June] they start to form silken nests, incorporating hairs and frass.  They develop orange dots on their backs.

Stage 5: [June-early July] silken trails are visible from the nest back up to canopy where they return to feed.

Stage 6: [Mid June-July] they have reached their maximum length of 35mm.  From mid June to September, they pupate in the nests, from which the adult moth emerges.  It lives for 4-5 days.

If you suspect you have come into either direct or indirect contact with OPM, you should contact either NHS Direct or a General Practitioner.


We use environmentally friendly Forestry Commission endorsed chemical called Dipel DF.  it is a living bacterium [Bacillus thuringienis] which when applied is ingested by the caterpillars.  We apply the chemical when it is most efficient between mid April – June.  For large sites and multiple trees, we use our specialist 4 x 4 Ultra Low Volume sprayer which can reach heights of 30m.  For single spot treatments we use a portable knapsack sprayer.  Later in the season we switch to manual nest removal with the aid of industrial vacuum cleaners to literally “suck” the nests and caterpillars off the trees.  The bags are then removed under contract by a specialist waste transfer company for incineration.

ATS specialises in OPM nest removal and we are the primary contractor for the Forestry Commission for the control of Oak Processionary Moth. Our experienced staff can offer a flexible, comprehensive and professional solution to your OPM control needs.  Please call us on 01483 210066 or email info@atstrees.co.uk for pricing enquiries.


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