1853 in the literal sense (witch-hunting is from 1630s), from witch (n.) + hunt (n.). The extended sense is attested from 1919, American English, later re-popularized in reaction to Cold War anti-Communism.
Senator [Lee S.] Overman. What do you mean by witch hunt?
Mr. [Raymond] Robins. I mean this, Senator. You are familiar with the old witch-hunt attitude, that when people get frightened at things and see bogies, then they get out witch proclamations, and mob action and all kinds of hysteria takes place. ["Bolshevik Propaganda," U.S. Senate subcommittee hearings, 1919]
type of poisonous spider (Latrodectus mactans) in U.S. South, 1904, so called from its color and from the female's supposed habit of eating the male after mating (the males seem to get eaten more often before they mate, when they first enter the webs of the females, which have very poor eyesight). Sometimes also known as shoe-button spider. The name black widow is attested earlier (1830s) as a translation of a name of the "scorpion spider" of Central Asia.