The oak processionary moth (OPM, lat. Thaumetopoea processionea) is a defoliating pest of oak trees. The oak processionary moth has been spreading throughout Germany for approximately 20 years and is increasingly found in urban areas also. The caterpillars of the oak processionary moth have poisonous setae which pose a health hazard to people and animals because they contain the urticating toxin thaumetopoein. The setae are very small (around 0.2 mm in length, around 0.005 mm in diameter). They will easily break away on contact and can remain toxic for several years. The setae are not only present on the caterpillars themselves which congregate in processionary groups from May to July, but they can also be found on the paths trodden by them and in their exuviae. They are also left in the cocoons which the caterpillars build prior to their pupation. Furthermore, the setae can spread through wind.

Upon contact, the urticating toxin thaumetopoein triggers irritations and inflammations to the skin and mucosa, including eyes and lungs. On the skin, particularly on directly affected areas such as arm, leg, neck and face, swelling and strong itching generally occurs within 24 hours. If untreated, such symptoms last for between two days and two weeks, depending on the degree of contact and the constitution of the individual in question. Inhalation of setae can cause inflammation of airways and breathing difficulties. Conjunctivitis and corneal inflammation can occur following contact with eyes. Systemic complaints such as dizziness, fever, and in rare cases, shock, have also been reported.

Protective measures against the risks to health posed by the setae

Organisational measures to prevent potential damage to health

• Avoid spending time in infested areas
• Oak trees are to be checked for infestation prior to forestry work
• All skin contact with caterpillars and cocoons is to be avoided
• Infested areas are to be isolated with the use of warning signs
• Do not eat, drink or smoke in infested areas
• Wash your hands regularly, even with suspicion of having touched the setae, and follow the skin care guidelines according to the skin protection plan
• Do not enter social areas during breaks when wearing contaminated work clothing
• Remove personal protection equipment (PPE) correctly and immediately after use, e.g. fold up protection suits with their outside facing inwards, and place in resealable bags, carriers or other containers
• PPE and any work equipment contaminated with setae, including motor vehicles, are to be cleaned appropriately
• To deactivate the urticating toxin, contaminated clothing is to be washed at a minimum temperature of 60 °C

Personal protective equipment (PPE, recommendation)

PPE should only be used as a protective measure if

• other measures, such as the avoidance of access, are impossible, or
• work such as pest control or tree cutting is only possible by accessing the infested area.

We also recommend:

• as a minimum, respiratory and eye protection should consist of an FFP2 respiration mask with exhalation valve and safety goggles (see BGR 190 and BGR 192).
• a protective suit which includes protective headgear, for example, a chemical protection suit according to DIN EN 14605 type 4B as well as closed, easily cleaned shoes, for example, Nitrile boots according to EN 13832-3 and impermeable protective gloves with mechanical durability appropriate to the intended work, should be worn.

Action in the event of physical complaints

In the event of physical complaints caused by the setae, or their suspicion, contact a doctor. Notify the doctor that EPS setae may be responsible for your physical complaint.

The oak processionary moth: pest control

Effective OPM control measures include biocidal treatments against caterpillars and the removal of cocoons.

Caterpillars are treated with chemical or biological biocides, ideally between hatching and third instar. Poisonous setae are present on caterpillars from third instar onwards. There are up to six instar stages until pupation. Further protective measures may be necessary in addition to the protective measures stated above.

In general, the following applies: Cocoons should be removed using a vacuum cleaning system (dust class H, possible pre-separator), as this reduces the risk of rendering setae airborne in comparison with other procedures.

The Federal Environment Agency has further information on the oak processionary moth, on protection against the caterpillars' setae and on control of the oak processionary moth.