Oak caterpillars defeat eradication effort
7 March 2011
The government has decided it is no longer practical to try to eradicate the growing numbers of oak processionary moth caterpillars, now established on oak trees across a wide area of west London not only defoliating the trees but also causing harmful allergic reactions in humans.
Instead, the Forestry Commission will try to limit populations to the five London boroughs where they are becoming an increasingly common sight, monitoring numbers and restricting the movement of oak out of the area, whether as plants or tree surgeons' prunings. The Commission is also establishing a buffer zone 10km (6 miles) around the area where any new outbreaks will be eliminated.
'Our experience on the ground and the scientific advice indicate that it was going to be almost impossible to completely eradicate it,' said the head of the Forestry Commission's Plant Health Service, Roddie Burgess. 'It is therefore clear that the wisest use of the available resources is to continue to work towards keeping it contained at the lowest practicable level within the current core outbreak area.'
Oak processionary moth (Thaumetopoea processionea) arrived in the UK from central and southern Europe about five years ago, probably on imported plant material. Its caterpillars move about trees in long nose-to-tail lines, giving the moth its name, and strip the foliage from a wide range of oak species and hybrids. Their tiny hairs, so light they can be blown about by the wind, also contain toxins which can cause painful rashes and asthma in anyone coming in contact with them.
There have been outbreaks in both Richmond Park and the Royal Botanic Gardens, Kew, where during a particularly bad infestation in 2009 the caterpillars attacked about 500 oak trees and 800 nests were destroyed.
Treatment includes spraying affected trees early in May to kill the caterpillars before they produce their poisonous hairs, and removing nests at the end of June and early July.
If you think you have seen an outbreak, however, don't try to handle the caterpillars or their nests yourself: instead report the sighting to the local council if in West London, or to Forest Research.