The Collaborative International Dictionary of English v.0.48:

Dor \Dor\, n. [Cf. AS. dora drone, locust, D. tor beetle, L.
   taurus a kind of beetle. Cf. Dormouse.] (Zool.)
   A large European scaraboid beetle (Geotrupes stercorarius),
   which makes a droning noise while flying. The name is also
   applied to allied American species, as the June bug. Called
   also dorr, dorbeetle, or dorrbeetle, dorbug,
   dorrfly, and buzzard clock.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Dorbeetle \Dor"bee`tle\, n. (Zool.)
   See 1st Dor.
   [1913 Webster]

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):

dorbeetle
    n 1: Old World dung beetle that flies with a droning sound