Why did so many caterpillars cross the road?

1st May 2011, Sunday

pale-grass-eggar
For the last few days there have been exceptional numbers of enormous (up to 60mm) hairy caterpillars crossing the private road along the Beach Reserve. These are unprecedented numbers of the Pale Grass Eggar Lasiocampa trifolii subsp. flava known only from shingle beaches in Kent and East Sussex. The larva feeds on a variety of grasses and plants including broom, creeping willow, heather and bramble. This glut of caterpillars is being enjoyed by Rooks and Cuckoos.

… and in more natural habitat!
on shingle