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Pine processionary moth (Thaumetopoea pityocampa)

Feeding on the needles of pine trees, the pine processionary moth is seriously destructive. They can rapidly strip trees of their needles in forests in Asia, Africa and southern Europe, leaving them vulnerable. Now, there are fears it’s heading north to the UK.

Pine processionary moths build characteristic fluffy nests in trees.

Credit: Daniel Heuclin / naturepl.com

Quick facts

Common name: pine processionary moth

Scientific name: Thaumetopoea pityocampa

What does it affect?: pine trees

Areas affected so far: not present in the UK

Origin: North Africa, southern Europe and the Middle East

What does pine processionary moth damage look like?

Symptoms include:

  • Presence of the large hairy caterpillars.
  • The caterpillars' nests in the branches and foliage of pine trees. They are white, silky webs that can reach the size of a football.
  • Discoloured needles (yellow and then brown) or completely eaten needles which leads to defoliation of the tree.
  • The extent of damage increases with severity of infestation and these signs and symptoms only become noticeable when populations are large and infestations severe.
  • If there are enough caterpillars they can defoliate the whole tree.

Credit: Dave Watts / naturepl.com

What is the pine processionary moth?

Adult moths have cream forewings with brown markings, white hindwings and a wingspan of 31–45 mm. The adults are difficult to distinguish from other species of moth.

The adults emerge from soil where they pupate and fly in the summer, no further than 1.7km. They live for only one to two days, during which time they mate and lay their eggs on pine needles. Females lay batches of 70–300 eggs. The eggs hatch in the autumn after 30–45 days and the emerging caterpillars feed on the needles of the trees. They then overwinter in their tent-like nests high in pine trees, and form processions on the ground in early spring before pupating in the soil until late summer, when they emerge as adult moths.

Where has the pine processionary moth impacted?

It is not currently thought to be present in the UK but is widespread throughout Europe. This pest has been expanding its range north through France since the 1990s, and is now breeding near Paris, so is getting closer to the UK.

Credit: Dave Watts / Nature Picture Library

How did the pine processionary moth get here?

The pine processionary moth has not reached the UK. The main risk of spread is during pupation as this occurs hidden in the soil and so is not obvious. Pupae may be present in the soil all year round as this stage can remain dormant and extend to two or three years, sometimes even longer. Worryingly, inspection is unlikely to detect pupae in the soil.

The main risk of spreading comes from imported plants. There could even be a risk of natural spread to the UK, since adult moths fly. Female adults can fly on average 1.5km in their lives, but the risk is still low compared to plant imports.

What impact will the pine processionary moth have?

This pest has the potential to reduced productivity of trees due to defoliation of the needles. It also weakens the tree which means it is more susceptible to other pests and diseases. Importantly these caterpillars also pose a significant threat to human health; they have toxic hairs, which can cause itching skin rashes, eye and throat irritation and breathing problems.

What are we doing about it?

To combat the spread of pests and diseases like the pine processionary moth, the Woodland Trust has:

  • Developed a UK 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.

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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. 

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What to do if you spot it

If you've spotted the signs and symptoms of the pine processionary moth report it to TreeAlert if you're in Britain or TreeCheck if you're in Northern Ireland.

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