Health Warnings Issued as Toxic Caterpillar Outbreaks Spread

The Forestry Commission is currently managing outbreaks of oak processionary moth (OPM) caterpillars, which possess toxic, hair-covered bodies capable of causing significant skin and respiratory irritation. These pests, which descend from oak trees in head-to-tail processions, have prompted official health warnings due to the risk of allergic reactions and skin rashes in humans and pets.

How to Identify Oak Processionary Moth Caterpillars

According to the Forestry Commission, OPM caterpillars are characterized by their black heads and bodies covered in long, white hairs. These hairs contain proteins that can trigger intense itching, eye irritation, and throat discomfort. In some cases, exposure can lead to breathing difficulties. Their nests are typically dome or teardrop-shaped and roughly the size of a tennis ball. While these nests appear white when fresh, they often become discoloured and brown over time.

Managing the Spread of Infestations

The Department for Environment, Food and Rural Affairs (Defra) is actively monitoring affected areas, including parts of Derbyshire and Dorset. The presence of the moth in Dorset was confirmed in 2025, marking an expansion into an area previously free of the pest. Authorities have responded to these sightings with extensive surveys and targeted control measures, such as the robust treatment of infested trees. The moth was originally introduced to England via trees imported from Europe for planting.

Public Safety and Prevention

Health officials advise the public never to touch the caterpillars or attempt to dispose of nests themselves. Because the toxic hairs can remain a hazard even after the caterpillars have moved or the nest has been abandoned, avoidance is the most effective precaution. If you spot a suspected nest on an oak tree, you should report it to the relevant local authority rather than attempting to remove it.

Key Takeaways for Public Awareness

• Health Risk: The hairs on the caterpillars contain proteins that cause itchy rashes, eye irritation, and potential breathing issues.
• Identification: Look for dome or teardrop-shaped nests on the trunks or undersides of branches of oak trees.
• Action: Never touch the insects or their nests. Report sightings to local authorities to ensure professional management.
• Environmental Context: The OPM is an invasive species in England, first introduced in 2006, and is now established in parts of the South East and Greater London.

As warm spring weather continues to favor the development of these insects, monitoring and management remain critical priorities for environmental agencies. By remaining vigilant and avoiding contact with infested oak trees, the public can minimize the risk of adverse health reactions during the active season.