A processionary caterpillar, Thaumetopoea processionea (family Thaumetopoeidae), which bears irritant hairs and can cause serious defoliation of oak trees.
Origin
1980s.
Definition of oak processionary in US English:
oak processionary
noun
A processionary caterpillar, Thaumetopoea processionea (family Thaumetopoeidae), which bears irritant hairs and can cause serious defoliation of oak trees.