Oak Processionary Moth (OPM)

OPM is a species of moth native to Southern Europe which was accidentally introduced to England in 2005-2006 and has since spread to the counties around London.

The caterpillars construct white webbing nests on trunks and branches of oak trees which resemble candy floss or cotton wool.

The caterpillar of this moth emerges in April every year and their tiny hairs can pose a health risk to humans and pets. The risk of exposure to these hairs is highest in May and June.

If you do come in contact with the caterpillar or its hairs please follow the NHS health advice.

See Forestry Commission interactive distribution map to see affected areas.

All sightings of the oak processionary moth should be reported to the Forestry Commission immediately.

Types of oak affected

Oak Processionally Moths (OPM) live almost exclusively in the following types of oak trees (Quercus):

Turkey Oak	Holm Oak	Turner’s Oak
English Oak	Sessile Oak	Algerian Oak
White Oak	Cork Oak	Italian Oak

Moth and Caterpillar life cycle

The moth lays eggs on an Oak tree in late August.
The eggs hatch between March – April (around Easter time) and caterpillars emerge and start to “process” around the tree looking for food.
By late Spring to early Summer the caterpillars become larger (20-25 mm) and are dark in colour covered with many white hairs.
Caterpillars retreat to the nest around late June-August to pupate.
New moths emerge a few weeks later in August and the nest is left redundant.
The new moths lay eggs on a nearby Oak within days of emerging and the cycle starts again.

Method of Treatment

There are two main options for dealing with the pest:

Manual removal of nests.
Pesticidal treatment: this is only suitable for early-stage caterpillars. The Forestry Commission may offer support for this.

Manual Nest Removal Timings

May-June: Generally caterpillars are nocturnal and so nest removal could be carried out during the day in this period; however, there is no guarantee that the caterpillars are in the nest so this may not be an effective time.
June-August: removing nests at this time is much more effective as all the caterpillars are likely in the nest in pupae stage.
After August: removing nests after the moths have emerged is not effective in controlling the spread of caterpillars but the nests do contain hairs so may be a threat to people and animals. In this case it might be wise to remove them but if there is no immediate risk to people and pets then the recommendation is to the leave the nests in situ.

Risks

It is the protein in the caterpillar hair which can cause irritation and allergic reaction in people and pets. In addition to being on the caterpillar the hairs may be loose or left in the active or dormant nest.

Symptoms to exposure to the hairs may include:

Itchy skin rash
Eye and throat irritation
Occasional breathing difficulties
In rare cases allergic reaction

Please follow the NHS health advice in the event of symptoms following exposure.

Nest removal procedure

⚠ DO NOT TRY AND REMOVE THE CATERPILLARS OR NESTS YOURSELF. ⚠

Full PPE must be worn by operatives in the tree where OPM is present including boiler suits, face masks, head covering, gloves etc. This PPE will be disposed of as bio-hazard waste following the removal operation.
Special OPM climbing kit will be used. This will be throughly cleaned after each removal and disposed of at the end of each season. This special OPM kit is not used for any other tree operations to avoid cross contamination.
Nests are sprayed with adhesive to ‘set’ the hairs to the nest and avoid contamination to workers, kit, and the surrounding area.
Nests are removed and controlled and are then dealt with as bio-hazard waste and sent off for incineration.