Question
hello i am in the UK recently i have seen two examples of what i can only describe as huge areas of webs on trees - example one was in the lake district on the back of skiddaw, a tree seemed to be "moving" from a distance, when approaching it we saw long hanging webs and pockets of webs literally all over the tree and hanging to ground level, the webs contained millions of black/brown maggots the tree was literally crawling, the tree looked as though it had been eaten alive, very little green foliage left and what was left was literally being eaten in front of us
tonight when out walking locally, we noticed a hedge (dyke as we refer to them locally) with webs over it, that part of the hedge is brown, devoid of any leaf, on close inspection the webs have tiny black spots in the centre i presumed to be eggs, looking higher, there again were these pocket webs with the maggots hanging, very few moving, must just be developing, i feel sure within 24hours that hedge will be crawling, the hedge is probably 200m long, could these things devour the whole hedge and what is this pest / disease we have seen, at 46years old and having lived rurally for many years we have never seen this before
thanks
MB

Answer
These are called The Lackey moth (Malacosoma neustria) is common across southern Britain and central Europe. Malacosoma species are notable for their caterpillars which are brightly coloured and form silken tents to regulate their temperature. Malacosoma neustria caterpillars are brown with blue, orange and white stripes. The adults are a fairly uniform brown. The larvae feed mainly on trees and shrubs from within their tents.

Tent caterpillars hatch from their eggs in the early spring at the time the leaves of their host trees are just unfolding. The caterpillars establish their tent soon after they leaf out. The tent is constructed at a site that intercepts the early morning sun. The tent covers the foliage and the caterpillars eat all the leaves in the tent and near the tent. The black specks are the fecal mater from the caterpillars.

A close relative is here in the US and is controlled with the use of an insecticide called Bt. Destroying the webs will also reduce the caterpillar population.