Source : Webster's Revised Unabridged Dictionary (1913)

Flea \Flea\, n. [OE. fle, flee, AS. fle['a], fle['a]h; akin to
   D. ?, OHG. fl?h, G. floh, Icel. fl?, Russ. blocha; prob. from
   the root of E. flee. ? 84. See {Flee}.] (Zo["o]l.)
   An insect belonging to the genus Pulex, of the order
   Aphaniptera. Fleas are destitute of wings, but have the power
   of leaping energetically. The bite is poisonous to most
   persons. The human flea ({Pulex irritans}), abundant in
   Europe, is rare in America, where the dog flea ({P. canis})
   takes its place. See {Aphaniptera}, and {Dog flea}. See
   Illustration in Appendix.

   {A flea in the ear}, an unwelcome hint or unexpected reply,
      annoying like a flea; an irritating repulse; as, to put a
      flea in one's ear; to go away with a flea in one's ear.

   {Beach flea}, {Black flea}, etc. See under {Beach}, etc.

Source : WordNet®

Pulex irritans
     n : the most common flea attacking humans