The Collaborative International Dictionary of English v.0.48:

Cockchafer \Cock"chaf`er\, n. [See Chafer the beetle.] (Zool.)
   A beetle of the genus Melolontha (esp. Melolontha
   vulgaris) and allied genera; -- called also May bug,
   chafer, or dorbeetle.
   [1913 Webster] Cockcrow

WordNet (r) 3.0 (2006):

cockchafer
    n 1: any of various large European beetles destructive to
         vegetation as both larvae and adult [syn: cockchafer,
         May bug, May beetle, Melolontha melolontha]