Oak Processionary Moth (OPM) caterpillars are considered a pest by the government's Forestry Commission (FC) who have urged Londoners not to touch them "under any circumstances".
The FC said that late spring to midsummer i.e. May, June and July was the "greatest risk period" for OPM caterpillars as this is the time of year they emerge and feed before turning into moths.
In a statement that described some of the risks posed by the moths, a spokesperson for the FC said:
"The oak processionary moth was first identified in London in 2006, and has since spread to some surrounding counties.
"The caterpillars and their nests contain hairs which can cause itchy rashes, eye and throat irritations, and should not be touched under any circumstances.
"The greatest risk period is May to July when the caterpillars emerge and feed before turning into adult moths."
Oak Processionary Moths are described as "pests", carry the risk of health problems as should not be touched "under any circumstances". Image: Environment Agency
The FC said OPM caterpillars can be identified by their nests, which are typically dome or teardrop-shaped, averaging the size of a tennis ball. "They are white when fresh, but soon become discoloured and brown," the spokesperson said.
The caterpillars themselves have black heads and bodies covered in long white hairs which "contain proteins which can cause itchy rashes, eye, and throat irritations".
"They can also occasionally cause breathing difficulties in people and pets, so should not be touched under any circumstances," they added.
FC Operations Manager Andy Hall added that some extra vigilance from people now hoping to enjoy greenspaces with the better whether is key to helping minimize risk when it comes to this particular pest.
He urged anyone who spotted the caterpillars to report them via the Tree Sightings website here.
Any sightings of the caterpillar should be reported to the Forestry Commission via its Tree Alert online portal.
Alternatively, people can email opm@forestrycommission.gov.uk or call 0300 067 4442.
