Warnings have been issued by local authorities across parts of England following an increase in sightings of oak processionary moth (OPM) caterpillars. These invasive insects, identifiable by their nose-to-tail movement and distinctive white hairs, pose a public health risk due to their toxic bristles. Councils are advising residents to exercise caution and avoid any contact with the caterpillars or their nests.
The caterpillars, which feed primarily on oak leaves, were accidentally introduced to England from mainland Europe in 2006 via imported oak trees. Since then, they have gradually spread, most commonly being observed in late spring and early summer. Their nests, made of a silk-like material, can vary significantly in size, from that of a 50p coin to a melon, and discolour to a dirty brown by August.
The danger from OPM caterpillars stems from their thousands of tiny, barbed hairs, which contain a toxin. If touched or inhaled, these hairs can cause a range of symptoms including itchy skin rashes, sore throats, breathing difficulties, and eye irritation. Public Health England has previously highlighted concerns about the potential for these hairs to trigger anaphylaxis-like reactions in some individuals.
Even without direct contact, the hairs can be shed by the caterpillars when disturbed and then carried by the wind, attaching to clothing, grass, and other surfaces. Groups particularly vulnerable to these health hazards include children, pets, people who work near oak trees, and anyone spending extended periods in infested areas. Grazing livestock and wild animals are also at risk.
If contact occurs and leads to skin or eye irritation, it is recommended to consult a pharmacist. For more severe allergic reactions, individuals should seek medical advice from a doctor or call 111. The Department for Environment, Food and Rural Affairs (Defra) leads a programme of surveys and controls to manage the OPM population and its spread, with current monitoring efforts in areas such as Derbyshire and Dorset where sightings have occurred.
The most crucial advice for the public is to avoid touching or approaching OPM nests or caterpillars. Children and pets should be kept away from affected trees, and no attempts should be made to remove the insects or their nests. Sightings on council land should be reported directly to the local authority, often with a photograph, though without risking direct contact.