An insect in the genus Melolontha, colloquially known as the Maybug, Maybeetle, or doodlebug. There are three species: the common cockchafer, the forest cockchafer, and the large cockchafer. They're an agricultural pest.

As for the name...

The name "cockchafer" derives from late 17th century usage of "cock" (in the sense of expressing size or vigour) + "chafer" which simply means an insect of this type, referring to its propensity for gnawing and damaging plants. The term "chafer" has its root in Old English ceafor or cefer, of Germanic origin and is related to the Dutch kever, all of which mean "gnawer" as it relates to the jaw. As such, the name "cockchafer" can be understood to mean "large plant-gnawing beetle" and is applicable to its history as a pest animal.