Extremely restless, jumpy. This vivid metaphor no doubt has survived because of its rhyming character, just as alliteration enhanced its seventeenth-century forerunner, a breeze (gadfly) in one’s breech(es). Several twentieth-century writers are credited with popularizing the phrase; among them are George Kaufman and Moss Hart, in The Man Who Came to Dinner (1939): “I’ll get the ants out of those moonlit pants.” The cliché also gave rise to the slangy adjective antsy, for restless or jumpy.