MYIAGRUS DEUS, in the heathen mythology, a name given sometimes to Jupiter, and sometimes to Hercules, on occasion of their being sacrificed to for the driving away the vast numbers of flies which infested the sacrifices on certain public occasions. The word is usually spelt Myiagrus; but this must be an error, as this word does not express the fly-destructor, but the mouse-destructor; and we have it sufficiently testified by the ancients, that flies were the only creatures against whom this deity was invoked. Pliny calls this deity also Myiodes; and tells us, that the flies which used to pester the Olympic rites went away in whole clouds on the sacrificing a bull to this god. We find in Athenaeus also, that this sacrificing to the god of flies at the Olympic games was a constant custom. Some distinguish these two deities, and tell us that the latter or Myiodes, used to visit the nations in vengeance, with a vast multitude of flies; and that, on paying him the due honours of a sacrifice, they all went away again; and this seems to agree with what Pliny tells us in some places.

At the time of the Olympic games, Jupiter was worshipped under the name of Apomos or Myiagrus Deus, to supplicate the destruction of those troublesome creatures. This happened only once in many years, when the sacrifices were performed there; but the Elians worshipped him continually under this name, to deprecate the vengeance of heaven, which usually sent, as they expressed it, an army of flies and other insects, toward the latter end of the summer, that infested the whole country with sickness and pestilence.