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Volunteers are hunting down an invasive species of bug threatening trees lining the streets of UK cities like London.

The plane lace bug damages trees by sucking out their sap, weakening the tree and making them vulnerable to other pests and diseases.

The bugs are particularly attracted to plane trees, which are a cross between American sycamores and Oriental planes.

They're a popular choice to plant in cities as they're tough and don't react too badly to pollution.

Environmental charity The Woodland Trust are now calling on 'Observatree' volunteers to look for the native North American bug, as they've been sighted in the UK for the first time in 18 years.

Observatree is a project set up by an organisation called Forest Research.

It aims to protect UK trees, woods and forests by identifying and reporting threats.

The Woodland Trust say the sightings are of "serious concern", and are asking people to keep a lookout for a yellowing on leaf veins which the bugs cause.

Vicky Bolton, Woodland Trust Citizen Science Officer, told ����ý Newsround: “The plane lace bug is an insect which is a big pest to plane trees. There are lots of these trees in London and other cities around the country.

“The adult bugs have milk-white lacy wings with some brown but they are tiny – only 2 to 4mm – like the size of a grain of rice. For such little critters they can cause huge damage when they attack a tree by feeding on its sap.

“They’re also really great at hitchhiking on vehicles, clothing or bags and with lots of planes (trees) in cities they can spread very quickly.”