gadfly

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

He that made that ryme in jeſt, little conſidered what a gad-fly may doe in earneſt. It is ſmall wiſedome to contemne the ſmalleſt enemy; the gad-fly is a little creature, but ſome little creatures be ſtingers; […]

Light fly his ſlumbers, if perchance a flight / Of angry gad-flies faſten on the herd; […]

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.

A person or thing that irritates or instigates.

There is a function for the gadfly who poses questions that many specialists would like to overlook. Polemics is healthy.

What was required now was the intervention of some men who were not gadflies. […] The logic of [Charles] Pearson's arguments was accepted, up to a point, by a consortium of businessmen. In August 1854, […] the consortium obtained royal assent for […] the Metropolitan Railway. […] In 1859, when it looked as though the Metropolitan Railway Company would be wound up with no line built, he [Pearson] wrote a pamphlet: A Twenty Minutes Letter to the Citizens of London in Favour of the Metropolitan Railway and City Station. Gadfly he may have been, but by this 'letter' he persuaded the Corporation of London to invest £200,000 in the line, a most unusual example of a public body investing in a Victorian railway.

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?

VVhere are thoſe gad-flies going? to ſome Junket novv; […]

A person who takes without giving back; a bloodsucker.

He’s a regular gadfly and takes advantage of his friend’s generosity.