How robbing starts

Robbing needs two things at once: a dearth outside and a target inside reach. The target is almost always one of three kinds of colony:

• A weak colony, with too few bees to guard every inch of its own entrance, cannot hold a determined attack.
• A queenless colony often stops defending altogether within days, its guards demoralized along with everything else.
• An exposed colony, one that has been opened for too long, had syrup spilled near it, or left with wet supers or bare comb sitting out, is broadcasting an invitation whether it is weak or not.

Strong, queenright, undisturbed colonies are rarely robbed out; it is nearly always the weakest hive in the row, or the one handled carelessly that morning, that pays for the dearth.