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Toxic caterpillar sightings soar 60 fold in a year, threatening Britain's oak trees

Author:  Sarah Knapton
Last Updated:  31/07/2019

Cases of toxic caterpillars which could wipe out Britain’s oak trees have risen 60 fold in a year, leading Britain’s Chief Plant Health Officer to issue an urgent plea for the public to look out for the pests.

In the last 12 months some 60 incidents of oak processionary moth have been reported inside Britain’s protected zone, compared to just one in the previous year.

The caterpillar – the larval form of the moth – feeds on leaves particularly from the European oak and if there are sufficient numbers can completely defoliate the tree, leaving it vulnerable to other pests, diseases and drought.The hairs from the caterpillars can also trigger asthma attacks and cause a mild rash and shortness of breath. Gardeners working near to infested oak trees have even reported becoming violently sick.

Nicola Spence, the government’s Chief Plant Health Officer, said:

“Our oak trees are under increasing threat from a dangerous tree pest – known as oak processionary moth.

“Members of the public and anyone working in green spaces can make a real difference by reporting any suspected oak processionary moth sightings.

“We are already doing a great deal to slow the spread of this pest in areas where it is present, in and around London, and eradicate findings when they happen elsewhere.

“Through our checks we have intercepted infested trees imported from other countries and introduced national legislation in 2018 to further strengthen import controls and checks.

“These interceptions have been vital due to the expansion of the pest’s populations in Europe, including the Netherlands, from where many oak trees are imported.

“Yet strong biosecurity relies on everyone playing their part, which is why I am calling for the public to check their trees and report any signs of oak processionary moth”

The species is believed to have arrived in Britain accidentally in 2005 via Dutch trees imported for a landscaping project at a housing development in Kew, South West London.

It has since taken hold in London and a protection zone has been drawn up around the capital to prevent infested oaks moving to other parts of Britain.

Since 2014 the UK has also had EU “Protected Zone” status around its borders, which restricts the import and movement of oak within the majority of the UK.

Imported oak plants in England have to be declared to UK Plant Health authorities so targeted checks for pests and diseases can be carried out.

But Defra is now so concerned about the possible spread that earlier this month it also banned imports of oak trees from any countries that are infected and will only allow specimens that have been monitored their whole lives.

Members of the public are urged to look out for nests which are typically dome or teardrop-shaped, about the size of a tennis ball. They are white when fresh, but soon become discoloured and brown.

The caterpillars have a grey body, dark head and long white hairs. They also move about in processions, from which they get their name and can sometimes be seen moving between oak trees on the ground as well as on the tree itself.

Matt Elliot, Conservation Advisor at The Woodland Trust said:

“We are extremely concerned to hear about the increased cases of oak processionary moth although we have not recorded any further incidences within our woodlands as yet. This pest is yet another pressure on our already stressed oak trees.

“Unfortunately oak processionary moth (OPM) has been imported once again into the UK on large oak trees from Germany and the Netherlands, despite the implementation of stronger import regulations last year.

“This pest, which causes allergic reactions in people and animals, could have been kept out of the UK if we had stopped importing large oak trees when the pest was first intercepted in 2005.”

The Woodland Trust warned that thinking of purchasing trees should consider where the trees may have come from and buy UK sourced and grown stock wherever possible to prevent such incursions in the future.

People should avoid approaching them but instead report them to the government tree health portal, Tree Alert or alternatively email opm@forestrycommission.gov.uk

Following the recent interceptions of OPM on recently planted oak trees, the <span class="bold blue&quot;>OPM webpage has now been updated to include the number of outbreak sites and 10km interception map.

July 2019 – Around 60 interceptions of OPM have been identified in the UK on recently imported oak trees. Affected counties in England include Cambridgeshire, County Durham, Devon, Dorset, Essex, Gloucestershire, Greater Manchester, Hampshire, Hertfordshire, Kent, Lancashire, Leicestershire, Lincolnshire, London, Merseyside, Middlesex, Nottinghamshire, Oxfordshire, Southampton, Staffordshire, Suffolk, Surrey, Warwickshire, West Midlands, Wiltshire and Yorkshire. Welsh Government have confirmed three cases in Glamorgan and Flintshire. Scottish Government have confirmed three cases in Fife, Inverness and Lanarkshire.

The regulations FAQ for stakeholders has also been published online.