Most Unwanted: Oak Processionary Moth

Human health risk: the caterpillars are covered in toxic irritating hairs. Do not get close to larvae or their nests. Take notice of any warning signs in place.

Can you identify the Oak Processionary Moth (Thaumetopoea processionea)?


  • Newly-hatched caterpillars have a brown body and dark head. As they grow, they lighten in colour
  • The caterpillars build nests (8 cm or larger) that form white silken clumps visible on Oak tree trunks from April to June, and leave white trails up stems
  • They also show a distinctive habit of moving about in late spring and early summer in head-to-tail processions, hence their name.

Plants affected:

  • Oak trees
  • They feed on many species in the family, including English Oak, Sessile (also known as Welsh Oak) and Turkey Oak.

UK status and other information:

  • They have a limited distribution in the UK
  • They were first found in trees in the west and south west of London in 2006. By July 2012, they had also been found in south London and Berkshire
  • They were accidentally imported on large Oak trees from continental Europe
  • There was a successful attempt to eradicate the caterpillars in Berkshire but they are more established in London
  • Oak Processionary Moth is native to central and southern Europe but is moving northwards, potentially due to climate change.

Why will any findings be important?

  • Oak Processionary Moth caterpillars feed on the leaves of oaks causing serious leaf loss. Large populations can strip whole trees bare of leaves, leaving them vulnerable to attack by other pests and diseases and less able to withstand other problems such as drought or floods.
  • They also pose a threat to human and animal health, as contact with the hairs can cause skin rashes and, less commonly, breathing difficulties and eye problems.

Could be confused with:

  • The Pine Processionary Moth, which has some similarities, but is more likely to be found on Pine trees, and seen at different times of year.

Useful links:


Images all © Forestry Commission