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Oak processionary moth (OPM) caterpillars, or larvae, are covered with thousands of minute, irritating hairs. These can be released as a defence mechanism, or blown off by the wind, and come into contact with people and animals. Contact can cause symptoms ranging from a mildly itching rash to allergic reactions.
The caterpillars build communal nests on the trunks and branches of oak trees to protect themselves from predators. Once released, the hairs can persist in the nests and the environment, such as on tree bark or grass, for a year or more, posing a long-term nuisance to people and animals unfortunate enough to come into contact with them.
To protect tree, public and animal health, the Government encourages owners of infested trees to engage tree or pest control professionals to destroy OPM caterpillars and nests. These workers, as well as others who work on or close to oak trees in the affected areas, are exposed to an occupational health risk which must be managed.
Picture: Henry Kuppen
Contact with the hairs, which contain an urticating (irritating) substance called thaumetopoein, is known to cause a number of conditions, including:
In very rare cases it can cause severe allergic reactions.
Some people can become sensitised by repeated exposure to the hairs, meaning that the symptoms become worse with repeated exposure.
Forestry workers and tree surgeons are at greatest risk of exposure because their work brings them into close contact with trees. Arborists, landscapers, gardeners and ground-care professionals, such as greenkeepers, are also at heightened risk because of the nature of their work and the amount of time they spend close to trees.
These workers should take particular care to protect themselves when working with or close to oak trees with OPM nests or caterpillars.
Such workers must therefore be vigilant, and their employers must employ an adequate occupational health monitoring system.
Before starting work on trees in the OPM-affected areas, consider the likelihood and risk of exposure to OPM and any mitigating measures which might be needed, for example:
When working in areas where OPM is known to be present:
The PPE required for those involved in nest removal is:
All of these items are readily available from good safety equipment suppliers.
Employers have certain responsibilities for their own and their employees’ safety. Their legal responsibilities are covered by the following legislation:
In general terms, employers are responsible for:
If in doubt, always consult a GP about OPM-related health incidents. Tell the doctor that you suspect contact with OPM caterpillar hairs.
For skin symptoms:
For eyeball and internal mouth, throat and nose symptoms, including breathing difficulties:
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