Quick facts

Common name: oak processionary moth

Scientific name: Thaumetopoea processionea

What does it affect?: oak species (species in the genus Quercus)

Areas affected so far: Greater London

Origin: central Europe

What does oak processionary moth damage look like?

The oak processionary moth feeds and lives almost exclusively on oak trees.

Symptoms include:

  • Caterpillars in procession on the trunk nose-to-tail in late spring and early summer. The procession is sometimes arrow-shaped with one leader and rows of caterpillars following.
  • Nests on trunks and larger branches of oak trees. They are made of distinctive white silken webbing that fades to a light brown colour.
  • Dislodged nests on the ground near oak trees.

What is the oak processionary moth?

The oak processionary moth is a species of moth with caterpillars that nest on oak trees. The caterpillars are covered in small hairs which can cause health risks in humans.

To minimise health risks:

  • Do not touch or approach oak processionary moth caterpillars or their nests.
  • Do not let children or animals touch or approach the caterpillars or nests.
  • Do not try and remove the caterpillars or nest yourself.
Oak processionary moths feeding on oak leaves

Credit: Blickwinkel / Alamy Stock Photo

What does it do to the tree?

There is one generation of oak processionary moth per year. The caterpillars hatch in spring and go through several instars, eventually developing the irritating hairs. The caterpillars descend lower down the tree as they develop, stripping the tree of its leaves as they go, leaving it vulnerable and weakened.

In summer, they retreat into nests and pupate. The adult moths emerge in late summer, living for only four days in order to mate. The female lays her fertilised eggs high in the tree canopy and the cycle begins again.

Where has the oak processionary moth impacted?

The oak processionary moth was mostly confined to Greater London, but in 2019 further imports of the pest led to expansion of its range.

Oak processionary  moth nest on a tree trunk

Credit: D Mark / Alamy Stock Photo

How did the oak processionary moth get here and what impact will it have?

The oak processionary moth was first found in London in 2006 and has been spreading ever since. 

It was accidentally imported to the UK in egg form in the canopy of trees for planting.

What are we doing about it?

To combat the spread and introduction of pests and diseases like the oak processionary moth we have:

  • Developed a UK and Ireland Sourced and Grown assurance scheme to make sure that all the trees we plant and sell are produced in the UK.
  • Lobbied the government to improve biosecurity at border points to stop new pests and diseases entering the UK.
  • Partnered with Observatree, a tree health citizen science project which trains volunteers to spot pests and diseases, thereby helping tree health authorities identify and manage outbreaks early.
Horse chestnut tree discoloured to yellow after a leaf miner infestation

Trees woods and wildlife

What we are doing about tree pests and diseases

We are fighting back against pests and diseases. Find out what we're doing to prevent the spread and protect the UK’s trees. 

Learn more

What to do if you spot it

If you spot the signs and symptoms of this pest outside, report it to the plant health authorities via TreeAlert if you are in Britain and TreeCheck if you are in Northern Ireland.

More pests and diseases: