CJS Focus on Trees & Hedges

Published: 19 November 2007

Logo: The Tree Council

In Association with: The Tree Council for National Tree Week

A new threat: Oak Processionary Moth (Thaumetopoea processionea), a native of southern and central Europe, has been found on oaks in London.  The moth was first noticed in the UK during the summer of 2006 breeding on oak trees in several west-London locations.

The caterpillars of the moth pose two problems. Firstly, their feeding can cause serious defoliation of oaks and secondly, they readily release tiny barbed hairs containing a toxin that causes severe skin irritation and allergic reactions in some people.

It is thought very likely that the moths were introduced as eggs on imported, semi-mature fastigate oaks used in a landscaping project.  The eggs are extremely difficult to spot and on hatching, the young caterpillars or larvae have a ready food source on the very trees with which they were imported.

Larvae may be found between April and July, feeding during the day in groups and congregating at night in communal nests.  The common name of the moth is derived from the larval habit of forming a single-file ‘procession’ between nest and feeding place.

Nests are made of silk webbing hanging under a branch or spun on the trunk, variable in size and form.  New nests are white and rather flimsy, while older larvae create larger, more solid looking structures, which darken as shed larval skins and hairs accumulate inside.  Empty nests remain a toxic hazard for a considerable time and should be treated with caution.

Larvae pupate in July and adult moths fly during August and September.

Oak processionary moth is not the only web-producer to be found in the UK. Apart from the brown tail moth, Euproctis chrysorrhoea, our native species do not cause any problems.


Further information and photographs of the oak processionary moth can be found on Forestry Commission website http://www.forestry.gov.uk/oakprocessionarymoth

By: Forest Research

Updated: Jan17

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