The larvae, or caterpillars, of Oak processionary moth (OPM) are a pest because they pose a threat to oak trees and to human and animal health. OPM caterpillars can strip whole oak trees bare of leaves, leaving them vulnerable to attack by other pests and diseases, and less able to withstand adverse environmental factors such as drought and flood. The caterpillars have thousands of tiny hairs contain an urticating, or irritating, substance called thaumetopoein, from which the species derives part of its scientific name. Contact with the hairs can cause itching skin rashes and, less commonly, sore throats, breathing difficulties and eye problems. This can happen if people or animals touch the caterpillars or their nests, or if the hairs are blown about by the wind. Further information about OPM can be found on the Forestry Commission website:
Last July a significant outbreak of OPM was discovered in the grounds of Royal Bethlem Hospital, at the Shirley end of Beckenham, in Monks Orchard Road. 4000 nests were removed from the Bethlem site alone. Within 24 hours Bromley tree officers also discovered 3 infected trees situated on Council property, and the nests were removed. Fortunately the number of local infected oaks has not risen as yet. However it is at this time of year that the grey hairy caterpillars are most likely to be seen ‘processing’ in their hundreds one behind the other on branches or along the ground.
The Bromley/Croydon OPM outbreak is being managed separately from other outbreaks in west London and elsewhere. The policy here is eradication while we still have a realistic chance of success. The Forestry Commission is currently co-ordinating a programme of chemical treatment to all infected trees in the London area and those within a 50 metre buffer zone of them. Specialist contractors are working around the clock in order to treat all the infected trees within the short window of opportunity in the caterpillars life cycle when the chemical is effective. The chemical, Bacillus thuringiensis (Bt), is derived from a micro-organism which occurs naturally in soil. It has been selected because it only affects a small range of species, namely just certain types of caterpillars. It is harmless to humans and animals such as dogs, cats and farm animals.
Please check any local oak trees that you know of. If you find or suspect OPM on a tree DO NOT TOUCH IT or go near it, please report it immediately. The contact details for reporting OPM are as follows:
- If oak is on public land – 020 8464 3333 Extn 3225 Julian Fowgies, Bromley Council
- If oak is on private land – 0131 314 6414 Forestry Commission Plant Health Section