Caterpillars of the oak processionary moth (OPM)

OPM caterpillars eat oak leaves and when present in large numbers, they can strip whole trees of their leaves, leaving them vulnerable to other threats and less able to withstand events such as drought and flood.

However, OPM caterpillars can be hazardous not only to oak trees, but to humans and animals in the vicinity. These caterpillars are covered in tiny, shedding hairs which can be blown on the wind and when they come into contact with people or animals, can cause irritating skin rashes, sore throats, inflamed eyes and in some cases, breathing difficulties.

OPM is a native species of southern Europe which was accidentally introduced to England and left uncontrolled, it would spread across much of Britain, risking our oak tree population and exposing people and animals to suffering. It is important therefore, that any sighting of the OPM caterpillar is reported to the council or Forestry Commission. Elmbridge Tree Services’ team of experts can help identify these pests and control them.

Caterpillars start emerging in April from eggs laid in oak trees the previous summer and the most effective control method is to spray affected oak trees with insecticide during the spring and summer while the caterpillars are present. The insecticide we use is not known to harm people, pets, or livestock. We also remove the caterpillars’ nests using vacuum equipment when the caterpillars are pupating into adult moths.

Oak Processionary Moth Caterpillars can be identified quite easily as they live almost exclusively in oak trees and move in nose-to-tail processions – a behaviour that gives them their name. The caterpillars also cluster together and build while, silken webbing trails and nests, which are usually dome or tear-shaped, on oak trunks or branches but not among the leaves.
If you think you have spotted these pests DO NOT APPROACH THE AREA.

For more information on the Oak Processionary Moth Caterpillar, visit