Oak Processionary Moth caterpillars

Oak Processionary Moth

Important information on Oak Processionary Moth and what you should do if you find the caterpillars or their nests.

What is the Oak Processionary Moth?  

The Oak Processionary Moth is an invasive insect pest of oak trees. Originating in central and southern Europe, it was accidentally introduced to the UK in 2006.

Cluster of Oak Processionary Moth caterpillars
A cluster of Oak Processionary Moth caterpillars

Why are they considered a problem?  

The caterpillars of the moth are covered in small hairs which can be a threat to human and animal health, causing persistent itchy skin rashes, eye and throat irritation and sometimes breathing difficulties in people and animals.  

In high numbers, the caterpillars can also cause extensive defoliation of oak trees, leaving them vulnerable to other pests and diseases, drought and climate change.  

When are the caterpillars active?  

The eggs of the moth hatch on oak trees in April. The caterpillars then develop through six stages during May, June and July, before retreating in to webbed nests to pupate. The adult moths then emerge in mid-August.  

Summer is the time of year when the processing caterpillars (following in line) are on the move and most visible. They may be found on the ground, and low on the trunk and branches of oak trees before forming webbed nests on any part of the tree.

How is The Royal Parks dealing with Oak Processionary Moth?  

The Government’s approach to Oak Processionary Moth is to control, not eradicate, the moth in the established outbreak zone and we adopt a rigorous management programme to control the moths and ensure the safety of park users and animals as far as is reasonably practical.  

In April and early May a limited and carefully targeted insecticide spraying programme takes place on some of the oak trees in the affected parks. In Richmond and Bushy Parks (as nationally designated nature reserves) this takes place with the consent of Natural England. The insecticide used is classed as non-hazardous to people but may be a temporary irritant during application. During the spraying operation some areas of the park may be temporarily closed to the public and marshals will be in place to direct people away from the area. Please follow any instructions on signage or given by the marshals to ensure a safe and enjoyable visit.  

This is followed by systematic surveying of oak trees for caterpillar nests during June, followed by nest removal In July/August which is carried out by specialist operatives using protective clothing and equipment. Although every effort is made to control the moth, some nests may still be present.  

What if I spot Oak Processionary Moth caterpillars or their nests?  

If you come across the caterpillars or their webbed nests, please do not touch them, keep children and pets away.

It is important that you:  

  • Do not touch or approach the caterpillars or nests 
  • Do not try to deal with them yourself. This requires specialist expertise and careful timing 
  • Warnchildren not to touch or approach caterpillars or nests
  • Keep pets away

If you or your child have already come into contact with an Oak Processionary Moth caterpillar or nest please seek medical attention. Similarly, if your dog has come into contact with a nest on the ground please seek advice from a qualified veterinarian as soon as possible.