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Oak Processionary Moth

The Department of Agriculture, Food and the Marine (DAFM) announced another finding of Thaumetopoea processionea, commonly known as the Oak Processionary Moth (OPM) in Ireland. Oak Processionary Moth caterpillars were found on four Oak trees in a Dublin housing estate in June 2023. The nests and four trees have been destroyed.

The first finding of this pest on the island of Ireland was discovered in a public park in Dublin in July 2020. 

Ireland is recognised as a Protected Zone under EU legislation for this pest based on years of official survey data. Ireland is the last EU Member State to be free from OPM. A Protected Zone is an area of the EU which is free from a quarantine organism despite favourable conditions for them to establish themselves.

The caterpillars (larvae) of this moth are mainly associated with feeding on the foliage of Oak (Quercus) tree species. However, when there are limited oak trees available, larvae have been observed to feed on other tree species (Acacia, Birch, Hornbeam, Hawthorn, Hazel and Beech) but it is uncertain whether they can survive on these species and complete their lifecycle development to adults. The caterpillars (larvae) feed on leaves and can cause severe defoliation leaving trees weakened and open to secondary infections from other pest and diseases.

In addition, this moth also poses a potential risk for human health and animal health, as the body of the caterpillar is adorned with numerous irritating hairs. Contact with the hairs can provoke allergic reactions which manifest as skin rashes, conjunctivitis and respiratory problems such as pharyngitis and asthma. Health problems can occur even if the larvae are not handled as the hairs break off readily and are dispersed in air currents. Abandoned nests contain shed skins, pupal cases and vast numbers of detached hairs and should be treated with extreme caution. 

Do not

  • touch or approach nests or caterpillars
  • let children touch or approach nests or caterpillars
  • let animals touch or approach nests or caterpillars
  • try removing nests or caterpillars yourself


  • warn children not to touch or approach the nests or caterpillars
  • seek medical advice if you think you or someone you care for has been seriously affected
  • see a vet if you think your pet or livestock has been seriously affected

Relevant publication

Further information