Oak Processionary Moth

Featured image: © By Luc hoogenstein, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=74852056

Issued by: The Department of Agriculture, Food & the Marine (DAFM).

Reason for issue: to notify the recent discovery of the Oak Processionary Moth caterpillars in Dublin, June 2023.

What was seen and when: Caterpillars of the Oak Processionary Moth were first reported in Ireland in June 2020 from a public park in Dublin, they were immediately removed and eradicated. A separate second finding of four Oak Processionary Moth caterpillars on Oak trees in a Dublin housing estate on 12th June 2023 was announced by the Department of Agriculture, Food and the Marine (DAFM). The nests and four trees have been destroyed.

Invasive status:

The Oak Processionary Moth has been risk assessed as a high impact invasive species. It is a regulated invasive pest under EU Plant Health legislation. Ireland has a Protected Zone status under the EU Plant Health legislation for this species. A Protected Zone is an area of the EU which is free from a harmful organism.

Summary of potential impacts:

• The caterpillars (larvae) feed on leaves and can cause severe defoliation leaving trees weakened and open to secondary infections from other pest and diseases.
• This invasive pest 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.

Identification features:

Note: Caterpillars of the Oak Processionary Moth can be confused with similar native species. See our ID guide for further details.

Caterpillars – Oak Processionary Moth

• Grey body and dark head
• Long white hairs protruding from reddish-brown warts along length of body
• Older caterpillars have a dark stripe along middle of back and whitish line along each side.
• Found living and feeding on ask tress
• Caterpillars cluster together while feeding forming ‘nose-to-tail processions’

Adult – Oak Processionary Moth

• Mottled grey to brown coloured wings
• Comma shaped marking in the centre of forewing
• Camouflaged well against the bark of an oak tree
• Wingspan is 30 – 40mm

Nests – Oak Processionary Moth

• Distinctive white webs
• Usually positioned on the underside of branches or on the trunk
• Small nests are typically tennis-ball sized but can grow much large

Introduction status: Two introduction events of the Oak Processionary Moth have been recorded, rapid response and eradication occurred on both occasions. Wider intensified DAFM survey did not yield additional findings in June 2020. In June 2023 surveying for this pest around the infected site has commenced and an intensive survey campaign using trapping methods and visual examinations of oak trees will continue over the coming weeks and months.

Pathway of introduction:

The first finding of this pest on the island of Ireland in June 2020 involved the discovery of a single OPM nest found on one imported, planted amenity tree. DAFM investigations are ongoing for the more recent sighing in June 2023 of caterpillars of the Oak Processionary Moth on oak trees in a Dublin housing estate. The main pathway of introduction is the importation of live oak trees for planting (horticulture).

Vector of spread:

The main vector of spread is planting live infested oak trees and secondary natural spread from an area of introduction.

Circumstances of the discovery:

The Department of Agriculture Food and the Marine announced that Oak Processionary Moth caterpillars were found on four Oak trees in a Dublin housing estate.

Management actions taken to date for this sighting:

• The Department of Agriculture, Food and the Marine have issued a press release and trader notice about the sighting and provided information to the general public on steps to take should any suspected sightings arise.
• The Department of Agriculture, Food and the Marine have commenced an investigation into this infestation. Surveying for this pest around the infected site has commenced and an intensive survey campaign using trapping methods and visual examinations of oak trees will continue over the coming weeks and months.
• The National Biodiversity Data Centre have developed information and identification profiles.
• The National Biodiversity Data Centre maintains an online reporting function: https://records.biodiversityireland.ie/record/invasives

Where might I see it? 

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.

What should I do?

• Suspected sightings in Ireland should be treated with extreme caution and notified immediately to the Department of Agriculture, Food and the Marine with your contact details and geolocation of the sighting by emailing [email protected] or by telephone 01-505 8885.
• Please circulate the species identification profile on this webpage.

Additional Resources:

• DAFM press release 2023 on Oak Processionary Moth
• DAFM Plant pest factsheet on Oak Processionary Moth
• Invasive Species Northern Ireland page for  Oak Processionary Moth.
• CABI ISC datasheet on  Oak Processionary Moth.

For queries relating to this discovery of Oak Processionary Moth in Ireland:

Contact the Department of Agriculture, Food and the Marine [email protected]

For general queries or information relating to invasive alien species:

Contact the National Biodiversity Data Centre Invasive Species Team: [email protected]

or email the NPWS [email protected] and see National Parks & Wildlife Service (npws.ie) or email [email protected]