Researching Irish peatlands, fens and wetlands - their ecology and conservation

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Oak processionary (Thaumetopoea processionea) is a moth whose caterpillars can be found in oak forests, where they feed on oak leaves, causing significant damage. 

They travel in nose-to-tail processions (hence their name), often arrow-headed, with a leader followed by rows of several caterpillars abreast. They are a human irritant because of their venomous setae (specifically urticating hairs), which can cause skin irritation and asthma.

Oak is its preferred food source, but the moth also eats the leaves of hazel, hornbeam, sweet chestnut, birch and beech.

In early summer they build silk nests on the trunks and branches, but not in the leaves, of oak trees, and leave silk trails on the trunks and branches. The nests and trails are originally white and visible, but soon become discoloured and hard to see. The caterpillars stay in these nests during the day between feeding periods, and later in the summer they remain in the nests to pupate into adult moths.

The moths pose an increasing nuisance to humans as their range is extended. The backs of older caterpillars (3rd to 6th instars) are covered with up to 63,000 pointed defensive bristles, sized between 0.2 and 0.3 millimeters, which contain an urticating toxin. These setae break off readily, become airborne and can cause skin irritation and itching, conjunctivitis and, if inhaled, respiratory distress, including asthma or even anaphylaxis.

The caterpillars are dealt with by biological pest control. (Source: Wikipedia)

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  • About me

    I am a Chartered Ecologist and a full member of the Chartered Institute of Ecology and Environmental Management (CIEEM). I am the author of numerous books and scientific reports and have published extensively in scientific literature.

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