The Collaborative International Dictionary of English v.0.48:

Scarabaeus \Scar`a*bae"us\, n.
   Same as Scarab in both senses.

WordNet (r) 3.0 (2006):

scarabaeus
    n 1: scarabaeid beetle considered divine by ancient Egyptians
         [syn: scarab, scarabaeus, Scarabaeus sacer]

The Devil's Dictionary (1881-1906):

SCARABAEUS, n.  The sacred beetle of the ancient Egyptians, allied to
our familiar "tumble-bug."  It was supposed to symbolize immortality,
the fact that God knew why giving it its peculiar sanctity.  Its habit
of incubating its eggs in a ball of ordure may also have commended it
to the favor of the priesthood, and may some day assure it an equal
reverence among ourselves.  True, the American beetle is an inferior
beetle, but the American priest is an inferior priest.