Also known as Hawthorn Webber.   There are two species of moths with caterpillars that can cause extensive defoliation of Cotoneaster and Hawthorn.   Small brown caterpillars feed beneath silk webbing.

The foliage becomes brown and dried up where small, dark brown caterpillars have grazed away the leaf surface, giving the impression that branches have died.   However affected areas will usually produce another flush of leaves and recover.  Hawthorn Webber moth larvae cover their feeding area with extensive sheets of fine white silk webbing.   Larvae of the moth live inside dense silk tunnels which incorporate leaf fragments and excrement pellets; this can be less obvious than the webbing of the Hawthorn Webber.

Whilst the appearance of this insect can be alarming and almost all of the foliage can become covered in webbing and turn brown; the plants usually recover without treatment and so control is not necessary.  Forceful spraying will be needed to penetrate silk webbing.