A jackal; a foil to another man's wit, a humble friend who plays into your hand to show you to best advantage. The jackal feeds on the lion's leavings, and is supposed to serve the lion in much the same way as a dog serves a sportsman. The dog lifts up its foot to indicate that game is at hand, and the jackals yell to advertise the lion that they have roused up his prey. (See Jackal.)
... the poor jackals are less foul, As being the brave lion's keen providers. Than human insects catering for spiders.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894