Source : Webster's Revised Unabridged Dictionary (1913)

Jigger \Jig"ger\ (j[i^]g"g[~e]r), n. (Zo["o]l.)
   Any one of several species of small red mites (esp.
   {Tetranychus irritans} and {T. Americanus}) which, in the
   larval or leptus stage, burrow beneath the skin of man and
   various animals, causing great annoyance. [Southern U. S.]