A tree-wrecking caterpillar that delivers a painful sting to humans, pets and livestock is spreading across the UK.

Caterpillars are covered in toxic hairs

The Government has admitted that attempts to eradicate oak processionary moth (OPM) from streets, parks and gardens in London have failed. It has now spread as far afield as Reading and Sheffield.

Caterpillars of the OPM are a menace to human health. Each 20-25mm bug is covered with 62,000 toxic hairs. The hairs easily penetrate clothes, causing skin irritation for up to a month.Other symptoms include vomiting, dizziness and fever.

In France, it’s reported that people have been blinded by OPM after its hairs came into contact with eyes.

OPM arrived from Europe on imported trees in 2006 and has been defoliating trees in five west London boroughs: Ealing, Brent, Hounslow, Richmond-upon-Thames and Hammersmith and Fulham.

“The only possible way to eradicate OPM is to cut down all oaks, and that isn’t going to happen,” said Henry Kuppen, who has pioneered caterpillar treatment in Holland.

Caterpillar hairs remain toxic for up to five years. Hairs are blown from trees and contaminate grass and soil. If fruit and vegetables are growing nearby, crops may be ruined.

OPM is tricky to control

Moths are airborne between July and September. They commonly spread along rivers and railway lines.

Tree expert Mark Townsend, of arboriculture firm Gristwood and Toms, said: “OPM survived extended freezing. There is no notion that cold winters will solve the problem – it will survive.”

The pest is so serious in Belgium that 30,000 moths were caught in just one night using traps. In Germany, police have sealed off infested areas and deployed helicopters fitted with sprayers to drench tree canopies with insecticide.

The Forestry Commission (FC) said it is no longer possible to enforce eradication in the London outbreak zone.

Council tree managers met last week to discuss the crisis. One described the FC’s move as “unbelievable”. Another said: “It’s a recipe for failure, a major threat to human health, and to the London Olympics.”



The insecticide deltamethrin, applied by specialists, has proved successful. In one region, only one nest survived in 19 trees treated. However, spraying chemicals into tree canopies is controversial and requires specialist kit and environmental impact assessments.

Blow torch

Popular in early outbreaks, nests were drenched with hairspray or glue to immobilise the hairy beasts, which were then fried with a blowtorch. The downside is that young trees were seriously burnt while the technique can spread toxic hairs over 100 metres.

Hoover ‘em up

In Holland, giant vacuums have been used to suck nests of caterpillars from trees, with their contents disposed of as hazardous waste. Mobile burning units have been deployed, where nests are vacuumed from trees and burnt on-site at 600°C, using incinerators (pictured above).



A natural parasite for OPM has proved to be 85 per cent effective. But it cannot completely eradicate caterpillars, while nematodes have to be sprayed into trees twice in the evening time.