Hedgerow defoliated by Caterpillars

Hedgerow defoliated by Caterpillars

Observation - Hedgerow defoliated by Caterpillars - UK and Ireland. Description: Several stretches of hedgerow, composed mainly of Hawthorn and Hazel, almost completely stripped of leaves. What is the caterpillar and is this degree of 'destruction' common?

Several stretches of hedgerow, composed mainly of Hawthorn and Hazel, almost completely stripped of leaves. What is the caterpillar and is this degree of 'destruction' common?