processionary moth

from The Collaborative International Dictionary of English v.0.48

Processionary \Pro*ces"sion*a*ry\, a. [Cf. LL. processionarius,
   F. processionnaire.]
   Pertaining to a procession; consisting in processions; as,
   processionary service.
   [1913 Webster]

   {Processionary moth} (Zool.), any moth of the genus
      {Cnethocampa}, especially {Cnethocampa processionea} of
      Europe, whose larv[ae] make large webs on oak trees, and
      go out to feed in regular order. They are covered with
      stinging hairs.
      [1913 Webster]