A breed of moths that feed on oak trees has infested several parks across London, causing allergic reactions to passers-by, and could cost up to £250,000 to remove.
The cost of dealing with a new pest which causes allergic reactions could cost as much as a quarter of a million pounds in the parks and open spaces cared for the City of London.
A new report also cautions that the infestation of oak processionary moth is reaching “a tipping point” at Hampstead Heath, which is a popular open space for Londoners and tourists alike.
The oak processionary moth is thought to have first arrived in the UK via trees imported from Europe in 2006.
Two years later it was recorded in Richmond Park and Kew Gardens; and experts believe it may have reached Hampstead Heath by 2014.
Caterpillars and nests can cause an allergic reaction in humans and dogs.
The moth feeds on oak trees, and “in extreme numbers” can strip the leaves from trees, according to the City Corporation’s director of open spaces Colin Buttery.
This financial year the authority’s parks team is likely to spend £100,000 stripping the nests from trees and spraying pesticide when eggs appear in the spring.
Mr Buttery warned that as the problem increases it could cost the City £250,000 a year.
In a report he said: “We are now reaching a ‘tipping point’ at some properties, such as Hampstead Heath, where nest numbers have grown exponentially in 2018.”
There were 15 nests on 13 trees on the Heath in 2015, but this had soared to 2,013 last year when nests were spotted on 680 trees.
He pointed out, however, that the number of reported health problems has remained low. People can suffer allergic rashes if they come into contact with the nests.
Mr Buttery said the number of nests is “relatively low” at Ashtead Common, in Surrey, which is a National Nature Reserve and has more than 2,000 ancient oak pollards.
There are also low numbers reported at Epping Forest and the City Cemetery & Crematorium, but he warned there are “likely” to be large increases in the number of nests and distribution of the pest over the next few years.
The City Corporation has “taken a zero risk approach” when nests are near places the public would be most at risk.
This means it is removing nests near car parks, popular paths, cafes and children’s play areas and sports facilities in the parks and open spaces it looks after.