Oak Processionary Moth (OPM)

Oak processionary moth (Thaumetopoea processionea) is a species introduced to London from southern Europe in recent years.

The caterpillars have thousands of tiny hairs which can cause irritation to human and animal skin and less commonly sore throats, breathing difficulties and eye problems. Severe caterpillar infestations can defoliate trees leading to a reduction in overall tree health.

For more information and advice about the symptoms and spread of oak processionary moth in England please see the Forestry Commission website.

Where is it located in the Borough?

Welwyn Hatfield Borough has been included in the "established zone" as it has spread outwards from London.

In the past years, we have found OPM in Northaw Great Woods near Cuffley, the Alban Way, Briars Lane in Hatfield and The Commons area of Welwyn Garden City. 

What should I do if I discover it?

Check on the Forestry Commission web site for identification images and videos of the moth in all it's different life stages.

  • do not touch or approach OPM nests or caterpillars
  • do not let children or animals touch or approach nests or caterpillars
  • do not try removing nests or caterpillars yourself and
  • avoid or minimise time spent under or downwind of infested oak trees, especially on windy days in summer
  • teach children not to touch or approach the nests or caterpillars
  • train or restrain pets from touching or approaching them
  • keep horses and livestock a safe distance from infested oak trees – cordoning off infested trees, covering and stabling can help.

If you suspect you have found an OPM nest or caterpillars anywhere in England, Scotland or Wales, please report it to us immediately via TreeAlert. Your reports will be assessed by the Forest Research scientists and forwarded to the plant health authorities for appropriate action.

What to do if you think you have come into contact with the caterpillar hairs

  • see a pharmacist for relief from skin or eye irritations after suspected OPM contact
  • call NHS on 111 or see a doctor if you think you or someone in your care has had a serious allergic reaction – tell the doctor you suspect OPM contact
  • consult a veterinary surgeon if you think your pet or livestock has been seriously affected – tell the vet you suspect OPM contact.