Oak Processionary Moth (OPM)

The Oak Processionary Moth (OPM) has been present as a pest in many European countries since 1995. Firstly originating from the Iberian Peninsula and spreading north through France, Belgium, Germany and Holland and is exclusively associated with oak trees. In Southern Europe, distribution of and the associated health and environmental issues associated with OPM are statistically less significant in comparison to Northern Europe. This being due to the presence of natural predators and to a lesser extent a more acclimatised niche in southern climes. Attributing dramatic global climate changes have pushed the range of OPM northwards. Without the presence of comparative natural predation an alarming amount of populations of the moth have sprung up and successfully colonised as far north as Sweden. Infestations of OPM caterpillars were first surveyed and monitored in Richmond upon Thames, London in 2006. Since then several monitoring and surveying bodies in addition to the Forestry Commission have been established to document and record the infestation.

The outbreak has reached disturbing proportions and the population of OPM has now broken out of the M25 in a number of areas, despite major and serious attempts of eradication. Slowing down the spread is now the realistic situation and avoiding outbreaks further afield in the United Kingdom. Advanced Tree Services is one of only three Forestry Commission endorsed contractors employed to tackle the pest via a number of resolutions. Our contracts include but are not restricted to; London Borough of Hammersmith and Fulham, Ealing, Merton, Epsom & Ewell, Royal Borough of Kingston upon Thames, Royal Parks and Wandsworth. Firstly though, why is it justifiable to remove the Oak Processionary Moth?

Tree Health Issues

It’s in the name; the Oak Processionary Moth. Oak trees are predominantly used as the host by the moth (Pedunculate/English oak Quercus robur, Sessile oak Quercus petraea and Turkey oak Quercus cerris mostly). Once populations of the larvae establish the emerging caterpillars strip and defoliate the tree. This reduces the trees capability to photosynthesise and repeated attacks, year on year, can place the tree under stress. This in turn can deplete the trees stored energy and natural defence systems, rendering it more vulnerable to other pests and diseases.

Health Issues

The following information is the product of direct advice and relevant research conducted by the Department of Health. The OPM is of a major health concern for several reasons. In its later stages (3rd to 6th instar growth stage) of its caterpillar development between late May and early June, the caterpillars are covered in minute hairs that contain an urticating toxin (thaumetopoein). If those hairs come into contact with the skin various persistent symptoms can occur. This includes but is not restricted to; an itchy rash, sore throats, conjunctivitis and respiratory problems and can therefore cause increased issues to those with pre-conditions. Stand alone, these symptoms are statistically non-fatal and usually predominantly leads to general uncomfortableness for up to 6 weeks after first contact (subjective). However, anaphylactic reactions are not unknown. Treatment is easily applied via the use of antihistamines despite the hairs remaining toxic for several years. If you suspect you have come into either direct or indirect contact with OPM, you should contact either NHS (111) or a General Practitioner. It is important to note that OPM has not caused any directly attributed fatalities. Animals including cats, dogs and horses can also be affected by the caterpillars irritating hairs and should be kept away from infested trees or fallen nests.

Example of OPM Rash


Once the window of pesticide application has closed (generally mid April to the end of May), we switch to nest and caterpillar removal operations. The nests can be located in all above ground areas of a tree, but prefer sheltered areas to nest, under branches on the trunk and even at the base of a tree. For heavily infested trees or areas with a high density of Oaks, our tracked Mobile Elevated Works Platform (M.E.W.P) can access rough terrain that may cause difficulties for other vehicles. With our trained and professional operatives we can adapt to any situation to succeed in the oak processionary moth removal. We have experienced extremely good feedback using this method as we aim for efficient removal with minimal damage and disturbance.

Oak Processionary moth nest removal can be undertaken using a high suction Type H industrial vacuum where possible. Our highly skilled climbers undertake manual removal higher in the canopy and the aim is to remove all evidence of nests, caterpillars and webbing. The bags of the vacuum, PPE and any manually collected nests are removed from site and disposed of. As the nests and Oak Processionary Moth are defined as hazardous biological waste, we use a hazardous waste carrier to destroy them. ATS adhere to the correct use of the essential Personal Protective Equipment (PPE). We aim for an efficient, environmental and ecologically friendly treatment unique to the situation.


At ATS, we use an environmentally friendly pesticide and specialist machinery to undertake the job of Oak Processionary Moth Treatment effectively, correctly and with minimal risk environmentally and ecologically. This coupled with our trained, competent and experienced operatives therefore ensures a professional and efficient treatment.

The pesticide we use is a living bacterium, Bacillus thuringienis (DiPel DF) which, when applied is ingested by the caterpillars. The bacteria breaks down the alkalinity of their stomach which leads to paralysation of their digestive organs and the caterpillar starves. Dipel DF is one of two pesticides endorsed by the Forestry Commission as a control method, the other one being Dimlin Flo.

At ATS we exclusively use Dipel DF as it targets caterpillars solely and breaks down easily within the food chain. It can be used over bodies of water and doesn’t affect aquatic organisms making it environmentally and ecologically friendly. We do pesticide applications when it is most efficient (between the 1st and 3rd instar (growth)) stages which is generally mid-April to the end of May. To apply the pesticide, we have two methods depending on the site and the degree of infestation. For large sites with multiple trees and vehicle access, we use our specialist 4X4 mounted Ultra Low Volume spray units which have a spray range of up to 30m. Imported from Italy and used during OPM treatment works since 2013, we have found these machines both invaluable and incredibly efficient. The Ultra Low Volume feature enables a dramatic reduction of water and pesticide usage and in addition to this, the spray unit is electrostatic. This means the treatment is positively statically charged and attracted to the tree leaves thus reducing drip and drift of the chemical once applied, further reducing the quantity of water and pesticide used. For single spot treatments and inaccessible areas, we use a backpack mister worked by an experienced operative. All our spraying operators are fully qualified to use the equipment. ATS adhere to the use of the correct Personal Protective Equipment and we provide a friendly, professional and efficient service unique to the situation.

OPM Nest Treatment