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Oak Processionary Moth OPM

The Oak Processionary Moth is a notorious pest that primarily targets oak trees. Originating from mainland Europe, OPM has gradually spread to different regions, causing significant concerns for the health of oak populations. The caterpillars of these moths pose a severe threat to both human health and the condition of oak trees.

Please do not attempt to remove the caterpillars or nests as these pose a threat to human health.

If you suspect you have a tree with OPM contact us and our team will be happy to assist.

OPM is currently being tracked by the Forestry Commission to help track outbreaks and its prevelance. Sightings of OPM nests or caterpillars should be reported to the Forestry Commission which can be done via TreeAlert.

01629 824079
Thompson Tree Services Pruning Trees

Identifying Oak Processionary Moth (OPM)?

Identifying an OPM infestation is crucial to initiate timely and effective measures. Key features of OPM infestation include:

  1. Nests: Oak Processionary Moth caterpillars build distinctive white, silken nests, usually found on the trunks or branches of oak trees.
  2. Caterpillars: The caterpillars are dark in colour, covered in fine white hairs, and move in processions, hence the name.
  3. Health Decline: Infested oak trees may show signs of stress, leaf loss, and decline in overall health.

Life Cycle

Oak Processionary Moth (OPM) undergoes a fascinating lifecycle, but unfortunately, this captivating process can lead to severe implications for oak trees and human health. Understanding the different stages of the OPM lifecycle is crucial in combatting infestations and protecting both our cherished oak trees and ourselves.




The lifecycle of the Oak Processionary Moth begins in the form of eggs. Adult female moths lay their eggs in characteristic clusters on the leaves, small twigs, or branches of oak trees during the late summer months. These clusters are covered with a protective layer of tiny hairs from the female's abdomen, providing insulation and safeguarding the eggs from external threats. The eggs remain dormant throughout the winter, with the onset of spring triggering their development. As temperatures rise, the eggs hatch, giving rise to the infamous OPM caterpillars.

The larval stage of the Oak Processionary Moth is the most destructive and notorious phase of its lifecycle. After hatching, the young caterpillars undergo several moulting stages as they grow. They emerge from their eggshells and immediately begin to feed on oak leaves, consuming vast quantities of foliage as they progress through their life cycle. One distinguishing feature of OPM caterpillars is their characteristic processionary behavior. They move in long, nose-to-tail lines, resembling a procession, which lends to their name. This behavior is particularly pronounced during their foraging expeditions and when they move to new feeding sites, seeking fresh leaves to sustain their rapid growth. The caterpillars' bodies are covered with thousands of tiny, barbed hairs, which are a major source of concern for human health. These hairs, when released, can become airborne and cause skin irritation, allergic reactions, and respiratory issues in humans and animals that come into contact with them.

After a few weeks of intense feeding and growth, the Oak Processionary Moth caterpillars reach full maturity. At this stage, they enter the pupal stage, wherein they encase themselves in silken cocoons for protection and transformation. Within the safety of their cocoons, they undergo metamorphosis, developing into adult moths. The adult moths have a wingspan of approximately 30 to 35 mm and are predominantly nocturnal creatures, meaning they are most active during the night time hours. Unlike their destructive larval counterparts, adult OPM moths do not pose any direct threat to oak trees or humans. Their primary focus is on reproduction and ensuring the continuation of their species. The female moths release a pheromone to attract male moths, and after mating, the females will lay their eggs, completing the lifecycle of the Oak Processionary Moth, and starting the cycle anew.

Our Specialised OPM Services

At Thompson Tree Services, we undertsand the urgency of dealing with an OPM infestation promptly and safely. Our specialist services include:

  1. Assessment: Our experienced arborists will conduct a thorough inspection of your oak trees to indetify any signs of OPM infestation. Surveys can be conducted throughout the year but are recommended from late March to May, as this is between the caterpillars emerging from eggs and starting to build their nests.
  2. Safe Removal and treatment: We employ safe and efficient methods to remove OPM nests and caterpillars from oak trees, minimising the risk to both your trees and your health. We offer preventative treatments to protect your oak trees from future OPM infestations, ensuring their long-term health and vitality.
  3. Education and Awareness: Our team is committed to educating our clients about OPM, offering insights on identifying early signs and promoting safe methods.

More information on treatement and removal can be found below:

Spray Treatment

Spray treatment is an essential tool in the fight against OPM caterpillars. This method involves applying carefully selected and environmentally friendly insecticides to the affected oak trees. The timing of the spray treatment is crucial and must coincide with the early stages of OPM caterpillar development to achieve maximum effectiveness.

Our certified arborists use targeted spraying techniques that minimise any potential impact on other beneficial insects and wildlife. The treatment is designed to specifically target the OPM caterpillars, interrupting their life cycle and preventing further damage to your oak trees.

Nest Removal

Nest removal is a critical step in controlling OPM populations and reducing their impact on oak trees and human health. OPM caterpillars construct distinctive silken nests on tree trunks and branches, and these nests house large numbers of caterpillars.

Our experienced arborists are equipped to safely remove OPM nests, following strict safety protocols to avoid direct contact with the caterpillars and their irritating hairs.

Specialised equipment and protective clothing are used to prevent any health risks to our team during the removal process. By eliminating the nests, we disrupt the caterpillars' feeding and breeding patterns, limiting their destructive impact on your oak trees and reducing the risk of exposure to the irritating hairs for both humans and animals. Once removed we follow strict guidelines to dispose of the hazardous waste.

Pheromone Trapping

Pheromone trapping is an innovative and environmentally friendly method to monitor and control the OPM adult moth population. Female OPM moths emit pheromones to attract male moths for mating. By strategically placing pheromone traps near oak trees, we can lure and trap male moths before they have a chance to mate, thus disrupting the reproduction cycle.

The pheromone traps are designed to be highly effective at attracting male moths, while ensuring they do not pose any harm to other beneficial insects. This method helps in reducing the number of eggs laid by female moths, thereby controlling the population of OPM caterpillars in subsequent generations.

Get in touch with us today

No obligation quote on the work

We assess the work required and aim to give you a quote within 2 working days of the site visit.
On acceptance of our quote, our team will undertake the statutory checks.
We will arrange with you a convenient date and time to carry out the work.
Our professional team will arrive at the agreed time and undertake the work.

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01629 824079

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