Old English stingan "to stab, pierce, or prick with a point" (of weapons, insects, plants, etc.), from Proto-Germanic *stingan (source also of Old Norse stinga, Old High German stungen "to prick," Gothic us-stagg "to prick out," Old High German stanga, German stange "pole, perch," German stengel "stalk, stem"), perhaps from PIE *stengh-, nasalized form of root *stegh- "to stick, prick, sting."
Specialized to insects late 15c. Intransitive sense "be sharply painful" is from 1848. Slang meaning "to cheat, swindle" is from 1812. Old English past tense stang, past participle stungen; the past tense later leveled to stung.
Old English stincg, steng "act of stinging, puncture, thrust," from the root of sting (v.). Meaning "sharp-pointed organ capable of inflicting a painful puncture wound" is from late 14c. Meaning "carefully planned theft or robbery" is attested from 1930; sense of "police undercover entrapment" first attested 1975.