Thousands of pounds are being spent to exterminate an invasive caterpillar able to destroy trees and cause allergic reactions in humans.

The Oak Processionary Moth (OPM) was introduced to the UK from Europe accidentally on an oak tree for a development project in Richmond, West London.

By 2008 the moth and its caterpillar form had spread to Richmond Park and Kew Gardens, where it had built communal nests and begun eating away at trees' leaves.

The tiny hairs on the caterpillars can cause severe asthma attacks and allergic reactions both by direct and indirect contact, leading the City of London Corporation - which runs the two green spaces - to tackle their numbers by spraying pesticides and removing nests.

While the process had kept populations at bay, a "tipping point" was reached in 2018 when best numbers grow hugely in places like Hampstead Heath, Highgate Wood and Queens Park - rising from 15 nests in 2015 to 2013 nests last year.

The Corporation's Open Spaces director Colin Buttery said: "At Ashtead Common; the City Cemetery & Crematorium and Epping Forest numbers are currently relatively low, but these properties are likely to follow the same trajectory of large increases in the number of OPM nests and distribution of this pest species over the next few years.

"The staff time resource and contractor costs will also increase markedly even with the targeted risk zone approach being taken."

As it continues its fight against the moth the Corporation is increasing its anti-pest investment tenfold compared to last year, spending £100,000 on nest removal, pesticide spraying, pheromone trapping and survey inspections.

In Epping Forest alone £8,000 will be spent to stop the currently small population getting out of hand.