The Lackey, Malacosoma neustria is a common species in the southern half of the UK.
The caterpillars hatch in the spring from over-wintered eggs and spin a silken web on a variety of foodplants such as Hawthorn (Crataegus monogyna), Blackthorn (Prunus spinosa) and Bramble (Rubus fruticosus agg.).
When small they live as a community inside the web where they grow rapidly before dispersing to find sheltered places to pupate. The adults fly later in the summer, in July and August.
Other moth caterpillars can be seen in the gallery of British moth caterpillars