gadfly

noun[before a noun]5

1. •
   Any dipterous (“two-winged”) insect or fly of the family Oestridae (commonly known as a bot fly) or Tabanidae (horse fly), noted for irritating animals by buzzing about them, and biting them to suck their blood; a gadbee.

   • Light fly his slumbers, if perchance a flight / Of angry gad-flies fasten on the herd; […] — 1749
2. •
   (figurative) A person or thing that irritates or instigates.

   • VVhat gad flye tickles so this Macrinus, / That vp-flinging thy tayle, he breakes thus from me. — 1620
3. •
   (figurative) A person who upsets the status quo by posing novel or upsetting questions, or attempts to stimulate innovation by being an irritant.

   • There is a function for the gadfly who poses questions that many specialists would like to overlook. Polemics is healthy. — 1977
4. •
   (disapproving, figurative) A person who takes without giving back; a bloodsucker.

   • He’s a regular gadfly and takes advantage of his friend’s generosity.
5. •
   (figurative) Synonym of gadabout (“a person who restlessly moves from place to place, seeking amusement or the companionship of others”).

   • VVhat VVinnie? VVife, I say? out of dores at this time! vvhere should I seeke the Gad-flye? — 1605