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People are being advised to beware of the oak processionary moth, a species that not only damages trees but also causes health problems for humans and animals. Now summer is here and we're spending more time outdoors, don't be tempted to go near the fluffy cocoons of caterpillars that may appear on oak trees. Never be fooled into thinking the unusual caterpillars with spiky hair are simply quirky but harmless. On the contrary, if you come into contact with them, they can cause rashes and even breathing difficulties. Should your dog inadvertently brush past a nest during a walk, you must visit the vet as a matter of urgency, as the consequences can be serious - and possibly even fatal.   What is the oak processionary moth? The caterpillars of the oak processionary moth are officially labelled as "pests" in the UK, due to the fact they are harmful to oak trees and people's health. They live almost solely on oak trees, building their nest and moving in nose-to-tail processions up and down the trees, or across the ground. This is how they got their name. Often clustered together, they build white, silken webbing nests and trails. The nests are commonly teardrop-shaped and can be seen on oak tree trunks, or on the branches. They do not build nests on the leaves, as the leaves form part of their staple diet. If a large number of caterpillars attack an oak tree, they can strip it bare fairly quickly. This leaves the tree vulnerable to other threats.   How many of the moths are found in Britain? A native species of southern Europe, the OPM was introduced to England by accident in 2006. It was first found in London. It was transported to the UK in egg form in trees shipped over from Europe for planting. If left uncontrolled, it would spread rapidly across Britain, leaving many of our wild oak trees in peril. The risks to human health could also deter people from visiting woodlands. Wild animals and pets could also be exposed to harm. As the number of moths grew, it would become increasingly expensive to try and control the population. According to the Forestry Commission, the oak processionary moth was once found at 70 UK sites, but a "swift and coordinated response" saw all of the infected trees and materials destroyed.   What are the main tree pests and diseases in Britain? Unfortunately, tree pests and diseases are common in the UK, aside from the oak processionary moth. One of the most prevalent diseases is Dutch elm disease, which has changed our landscape forever and is still known to be spreading in the north of the country. It has wiped out millions of elm trees over the past four decades. Another dangerous pest is the great spruce bark beetle, which severely damages spruce trees when it tunnels into their bark. No one is sure how it arrived in the UK, although it was first found here in 1982 - there is evidence it may have been here as early as 1973. Like the oak processionary moth, it may have been accidentally transported here in untreated wood shipped over from Europe and Asia. The beetle is now established in the west of England, southern Scotland and Wales. When a large number of beetles infest a tree, it can become so badly damaged that it can no longer carry water up from the roots. A wound can appear, which will not heal. Everything above it will ultimately die. This can be disastrous if the main trunk is damaged. Scientists and wildlife experts are doing everything in their power to control the pests and diseases affecting Britain's trees, with the oak processionary moth being one of the most serious risks to people and nature.   What health problems does the moth cause? Thousands of minute hairs contain a substance called thaumetopoein, which can irritate people and animals. If your skin comes into contact with the hairs, it can cause itching and rashes. Other less common symptoms can include a sore throat, eye irritations and even breathing difficulties, in both people and animals. This is why vets advise dog owners to quickly move pets away from oak trees if they spot an infestation. If you're out walking and your dog comes into contact with the caterpillar, there's a good chance the hairs will get into your pet's nose or mouth and become trapped there. The initial reaction can be drooling, followed by swelling of the tongue.   What is being done to eradicate the danger? Some local authorities put up warning notices in an area where there is known to be an infestation of oak processionary moths. You should heed the warnings and try to avoid the area. At the very least, don't let your dog off the lead, or allow him to sniff around in potentially infested areas. The Woodland Trust, the Forestry Commission, landowners and local authorities have joined forces across the UK to control this pest. The aim is to protect our oak trees and enable people to safely enjoy woodlands, parks and gardens. The government is coordinating the national programme to minimise the threat of the moth. It has collaborated with various wildlife charities, including Observatree and the UK Plant Health Service, to carry out measures to protect our woodlands. The joint task force has eradicated the majority of threats from the moths by reacting quickly to sightings. While the moth is still established in much of Greater London and some of the surrounding counties, the rest of the UK has been designated a Protected Zone. When the government's Department for Environment, Food and Rural Affairs is notified about oak processionary moths in the Protected Zone, they seek the source, identify how big the problem is, notify counterparts in other parts of the UK and then eradicate the infestation swiftly. In June 2019, during a regular inspection of oak trees, the government's plant health inspector noticed newly planted trees from the Netherlands were infested with the OPM caterpillars. The outbreak was nipped in the bud, thanks to the routine inspection. Since the programme began, more than 2,000 shipments of oak from the Netherlands, Belgium and Germany have been found to contain the caterpillars. As a result, the government advised plant nurseries and landscapers to urgently check their trees. Volunteers from Observatree, the network of more than 200 specialist volunteers, undertook further survey activities to spot the tree pests. Emergency measures were introduced to strengthen the legislation following the most recent outbreak in 2019.   What should you do if you spot the moths? The Woodland Trust and the Forestry Commission are helping to coordinate the eradication programme and advise the public to report any sightings of the dangerous moths. This includes if you see the nests or caterpillars, whether on oak trees, or walking along the ground in their familiar "procession". You can report a sighting online via https://treealert.forestresearch.gov.uk/ or email the details to [email protected] – these are the preferred methods of making a report. Alternatively, you can ring 0300 067 4442. When submitting a report online, please include photographs. Always give precise details of the location. No one wants our ability to enjoy woodland walks to be compromised due to the risks posed by the oak processionary moth, so join the national campaign to keep its numbers down and report any sightings.