The picture above shows a Brown Tailed Moth Caterpillar on a young hawthorn in late September 2008.
This is the typical Brown Tailed Moth 'tent'. The adult female lays eggs in late Aug/early September and the very small caterpillars that hatch then collect together to form a gossamer 'tent' on twigs on the hawthorn. Between 100 and 200 little caterpillars then take up residence and overwinter. Removal of these 'tents' in late autumn and winter effectively removes the infestation and damage that these caterpillars wreak in the next spring; they will strip plant after plant of all leaf.