I spotted this web on a Hawthorn branch and went to investigate.
Small Eggar Moth Caterpillars
This is now a scarce and local species, due to the gradual destruction of the hedgerows. The adults which fly in February and March are rarely seen, but the larvae, live gregariously, on the Blackthorn and Hawthorn branches in the hedgerow.
It is now restricted to a few scattered collonies in England and Ireland and a few in Wales.
Such a fantastic find!