Oak Processionary Moth (OPM): Risks & Control in the UK

Oak Processionary Moth (OPM) in the UK

Threats to Oak Trees and Public Health

The oak processionary moth (OPM) is an invasive pest that poses significant threats to oak trees and human and animal health. Accidentally introduced to England in 2005, OPM larvae (caterpillars) feed on oak leaves, potentially defoliating entire trees and making them susceptible to other diseases and stressors.

Government Control Measures and Protected Zones

The UK government has implemented a comprehensive program to monitor, control, and minimize the spread of OPM. Most of Greater London and some surrounding counties are established OPM areas. To prevent further incursions, the rest of the UK is designated as a Protected Zone (PZ) under European Union regulations, with restrictions on the movement of oak plants.

The Forestry Commission, Animal and Plant Health Agency (APHA), and devolved administrations have taken swift action to eradicate newly introduced OPM populations. Ongoing efforts include tracking and inspecting oak imports, conducting field surveillance, and destroying infested trees and caterpillars. As a result, stricter import regulations for most oak species have been introduced to enhance protection against this pest. For more details, refer to the 'Official Action' - July 2019 section below, which also includes information on the OPM-free area declared in Italy in 2019.

Health Risks and Vulnerable Groups

OPM caterpillars develop hairs containing thaumetopoein, a protein that can cause severe skin irritation, rashes, eye problems, sore throat, breathing difficulties, and in rare cases, allergic reactions in humans and animals. The risk of exposure is highest in May and June when caterpillars shed hairs if disturbed or threatened. These hairs can become airborne, accumulate in nests, and stick to surfaces like logs, branches, grass, clothing, and equipment used by forestry and tree care workers.

Vulnerable groups include:

• Children and pets
• Individuals working near oak trees
• People spending time in infested areas
• Grazing livestock and wildlife

The image above illustrates the defoliation caused by OPM caterpillars on a London oak, while the other image depicts the characteristic rash resulting from contact with the hairs.