If you go down to the woods today, watch out for oak processionary moths, advises Sutton. Sutton residents are being advised by Sutton Council to be on the lookout for oak processionary moth caterpillars when visiting the borough’s parks this spring as the moths can cause an allergic reaction.
The oak processionary moth (Thaumetopoein processionea) is a pest that was recently identified in the Worcester Park area in the west of the borough. The moth was introduced to England from mainland Europe and first identified in London in 2005.
The oak processionary moth caterpillars emerge around May, coinciding with bud burst when leaves emerge from trees at the start of the growing season. In their early stages of growth, the newly-hatched caterpillars feed exclusively on oak leaves and it is possible for large populations to strip whole trees of their leaves. On a healthy oak tree, this generally will not cause any permanent damage, but it can leave trees vulnerable to other pests and diseases, and less able to withstand events such as drought and flood.
As the caterpillars develop they produce thousands of tiny barbed hairs containing a substance called thaumetopoein that can cause itching skin rashes, eye irritations and sore throats in people and animals that come into contact with them. In rare cases the barbed hairs can cause breathing difficulties and allergic reactions. However, symptoms are not usually serious and can be treated by a pharmacy.
The hairs can be shed by the caterpillars as a defence mechanism, be blown off by the wind, and left in the silken webbing nests the caterpillars build on the trunks and branches of oak trees, sometimes at or close to ground level. These nests can fall to the ground, and hairs can stick to the trunks and branches of oak trees.
The oak processionary moth caterpillars have a distinctive habit of moving about in or under oak trees in nose-to-tail processions, which gives them their name. The silken webbing nests are white when new, and often have silken trails leading to them. They quickly become discoloured and harder to see against the dark colour of oak-tree bark.
Sutton Council’s Parks Service is monitoring the situation closely and has a term contractor to deal with both spraying and nest removal.
Cllr Jill Whitehead, Chair of the Environment and Neighbourhoods Committee at Sutton Council, said:
“If you see any oak processionary moth nests or caterpillars, do not approach or touch them. Report them immediately to the council or the Forestry Commission, which is leading efforts to control its population, spread and impact.”
The main risk period is between now and July, when the caterpillars are active. However, borough residents are advised to avoid nests, even “spent” nests, at any time, because the hairs in them can remain irritating for many months.