The Collaborative International Dictionary of English v.0.48:

June \June\, n. [L. Junius: cf. F. Juin. So called either from
   Junius, the name of a Roman gens, or from Juno, the goddess.]
   The sixth month of the year, containing thirty days.
   [1913 Webster]

         And what is so rare as a day in June?
         Then, if ever, come perfect days.        --Lowell.
   [1913 Webster]

   June beetle, June bug (Zool.), any one of several species
      of large brown beetles of the genus Lachnosterna and
      related genera; -- so called because they begin to fly, in
      the northern United States, about the first of June. The
      larv[ae] of the June beetles live under ground, and feed
      upon the roots of grasses and other plants. Called also
      May bug or May beetle.

   June grass (Bot.), a New England name for Kentucky blue
      grass. See Blue glass, and Illustration in Appendix.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

June bug \June" bug`\, n. (Zool.)
   1. See june beetle.
      [PJC]

   2. A firefly. [Chiefly Northern U. S.]
      [PJC]

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]

WordNet (r) 3.0 (2006):

June bug
    n 1: any of various large usually brown North American leaf-
         eating beetles common in late spring; the larvae feed on
         roots of grasses etc. [syn: June beetle, June bug, May
         bug, May beetle]