Oak Processionary Moth

Oak Processionary Moth - The Blue Tree Company

If you’ve spotted our teams at work around an Oak Processionary Moth nest this information will help you learn more about why we are there and what we are doing.  

Oak Processionary Moths are pests of oak trees, and a hazard to human and animal health. 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.

What is the OPM?

OPM is the common term for the Oak Processionary Moth (Thaumetopoea processionea). They were thought to have been accidentally brought over from imported trees from continental Europe in 2005.  It was first confirmed in Richmond in 2006. This led to an investigation by the Environmental Health Service. Worryingly, it is spreading in all directions rapidly and now inhabits all boroughs of London and the adjoining counties.

OPM eat almost exclusively Oak leaves and spin spiderweb like nests to protect themselves in large groups. These can range in size and be as big as a rugby ball. They can be found at ground level as well as in anywhere in the main canopy.

opm in a group


When migrating from the nest to the feeding grounds the caterpillars travel in a chain nose to tail giving rise to the name Oak Processionary Moth.

opm nest


How can you 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.  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.

Oak Processionary Moth - The Blue Tree Company

What’s the problem with OPM?

There are health risks when we come in to contact with OPM or more specifically their hairs, also known as urticating hairs, that protect the caterpillars from predation.

Each individual hair, and there can be hundreds of thousands on each caterpillar, are tipped with a sharp barb loaded with a protein called Thaumetopoiene which acts as a toxin when introduced to the body. The hairs can remain active for many years even after they have been shed from the host.

The most common complaint from contact with the OPM hairs are a rash or blisters on the skin which can be very uncomfortable for several days, or even months, after contact. The problems can be a lot worse if the hairs get in to the eye or throat. Other less common symptoms that have been reported are fever, dizziness and vomiting.

Why can’t we control the spread?

This species has been particularly difficult to control due to a number of factors. In fact, Holland have been trying to eradicate OPM for 30 years without success.

  1. The frequency that the eggs hatch. Eggs will typically be laid from July To September. In rows a single egg deep with a distinct scale appearance. This can have a significant number of eggs, up to 300, in a plaque formation. Some, but not necessarily all the eggs, will hatch the following spring. It is the eggs that decide not to hatch from the same plaque, in the same year, that make it difficult to target with eradication methods such as insecticide spraying.
  2. There are currently no insecticides that only target OPM. This means that treatment of large woodland areas rich in Oak trees would also decimate the other native species so vital to our eco system. This is something we cannot do and means that populations are allowed to survive in order to protect others.
  3. This a relatively new invader and is still is relatively unknown, even within the arboricultural industry outside of London, let alone the private tree owners. This would suggest that populations of OPM are either misdiagnosed or missed completely.

What are the control methods available?

Identified nests can be removed by trained personnel under highly controlled conditions.  Given the serious nature of coming into contact with OPM hairs specialist protective clothing is worn to safely remove the nests.  

What should you do if you find a nest?

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.  We have trained professionals on our team here at The Blue Tree Company who can safely remove nests. Please contact Alan Randall on 01462 450203 or email info@thebluetreecompany.com

Brian WrightBrian Wright
17:46 04 Mar 22
The team worked very closely with us throughout their visit to give us exactly what we were hoping for in our small garden.Tidying up was excellent as usual.
kern joneskern jones
13:49 04 Mar 22
I am delighted to say what a great service the teams from The Blue Tree Company always provide. They are skilled and conscientious and always leave the property looking so much better than before they arrived. Not a stray twig left on the grass or in a bush - everything tidied away. Fantastic work.
Marianne BondMarianne Bond
23:13 01 Mar 22
Knowledgeable, personable and tidy up afterwards. We've used them several times for various tree work and always found them good.
16:35 19 Nov 21
Blue Trees were recommended to me by a neighbour who has been using them for several years. I was impressed with the professionalism, knowledge and punctuality of the whole team-from Fred who came to quote, through to the three men who came to carry out the job. They worked quickly and tidily and made sure I was completely happy before leaving. I have no hesitation in recommending Blue Trees to family and friends and would certainly use them again in the future.
Annabel PearceAnnabel Pearce
21:21 18 Aug 21
Job done very well. Helpful and approachable company. Thankyou.
Linda DenningLinda Denning
09:16 02 Jul 21
We have used Blue Trees on a number of occasions now and most recently yesterday to take down a tall tree. As ever they are very professional, neat and tidy and reasonably priced. We had requested they leave the wood with us and my husband would chainsaw it for our neighbours. The fact that they left the whole tree in very manageable chunks without being asked was a real bonus as it will save my husband a huge amount of time and effort. Thank you to all the team. We will use you again and would not hesitate to recommend you to others.
David DeeDavid Dee
11:39 02 Mar 21
We employed the Blue Tree Company to remove a couple of Laurel Hedges and grind out the stump of a 30 year old Birch tree that we had felled last year all in preparation for new turfing. The guys turned up on time on the day as planned, carried out the works efficiently and when finished cleared up behind them.We had an invoice query that was resolved promptly to our satisfaction.All in all we had a very positive experience of The Blue Tree Company
Tracy LynchTracy Lynch
21:21 10 Sep 20
Professional company from first contact. Quote provided on basis of photos during lockdown. Future appointment booked due to bird nesting season. Update email to confirm attendance/appointment time day before. 3 friendly capable staff Mark Callum and Brandon. Explained what they were doing reassured us. Cut very ugly tree to look as pleasing as possible from our side. Cleared up the site before leaving. Would definately recommend.

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