Oak Processionary Moth (Thaumetopoea processionea), commonly known as OPM, is a regulated pest in the UK that poses risks to oak trees, public health, and animals.
Do not touch OPM caterpillars or their nests.
If you suspect OPM activity in your oak tree(s), Connick Tree Care’s trained and competent arboriculturists can provide professional support. The appropriate management approach depends on the stage of the OPM life cycle.
- During the larval stage (typically April–May), control may involve the use of approved biological or growth-regulating treatments, applied in line with current legislation and best practice.
- Outside of the larval window, management may involve the specialist manual removal of nests, undertaken by operatives with the correct training, equipment, and controls in place.
Connick Tree Care does not support the use of pyrethroid-based insecticides, due to their significant adverse impacts on pollinators and other non-target species.
OPM was first identified in the Elmbridge and Spelthorne areas of Surrey in 2006 and has since spread across much of Greater London and parts of South East England. As such, ongoing monitoring and management are essential.
Although named the Oak Processionary Moth, it is the caterpillar stage that presents the primary risk. After hatching, caterpillars feed on oak foliage, progressively defoliating the crown. Repeated or severe defoliation can weaken trees, increasing susceptibility to secondary pests and disease.
OPM caterpillars possess thousands of fine, toxic hairs that can cause skin irritation, rashes, eye problems, and, in some cases, respiratory issues in people and animals. These hairs are easily shed, can be carried by the wind, and accumulate in nests, creating a long-lasting hazard even after caterpillars have moved on.
For sites with a large oak population, Connick Tree Care’s arboricultural consultancy team can undertake structured surveys, record tree data, assess risk, and develop proportionate management plans to optimise resources and ensure compliance.
Timing is critical to effective OPM control. Interventions must align with the pest’s life cycle to ensure treatments are both effective and lawful. If you have concerns or require advice, please contact Connick Tree Care and one of our professional arboriculturists will discuss your requirements.
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