1. The very torment of which they are so capable may be turned into a visitation of _judgment_. When Isaiah refers to the scattering of the Ten Tribes, he exclaims, "The Lord shall hiss for the fly that is in the uttermost part of the rivers of Egypt, and for the bee that is in the land of Assyria" (Isa. vii. 18). And the children will remember that the ten plagues which fell upon Egypt included "swarms of flies" in all the houses of the Egyptians. These little insects were used as the scourges of mankind to wreak the vengeance of a broken law on the heads of the transgressors. And especially is this the case with the law of cleanliness. The one sin that the fly will not tolerate is the sin of laziness and dirt. Wheresoever the filth is, there will the flies be gathered together. Those who despise this first law of their being will not offend with impunity; and if no other scourge be available, that little torment—the common fly—will be commissioned to undertake the duty. 2. But the sword they wield is double-edged. It not only flays the law-breakers, it also slays the infection and the fever which have followed in their train. They are _the scavengers of the atmosphere_. They do for the air what the pariah dogs of the East do for the earth—they gather up and remove everything that offends, everything that occasions or breeds disease. Let no one say that the swarms of flies bring the cholera and the fever. They are the camp-followers who tread on the heels of those dreaded foes, and they feed upon and do their best to remove the foulsome odours. We need not grudge the spider his savoury morsel, but it will be a dark hour for the earth if he should gain the mastery. If he should prove too much for the fly, we shall be left to the miasmas and pestilences from which the presence of the fly relieves us. 3. Even in its death the fly renders a most substantial service. It forms the food of innumerable song-birds, which, apart from the fly, would never be found in our land at all. How dull and lifeless would the months of the summer be without the swallow, the willow-warbler, and the fly-catcher. And yet these feed almost entirely on flies. "And if the trout had not discovered what a savoury morsel the fly is that dances on the stream, what a very dull, stupid amusement would fishing be! Many a schoolboy would lose the greatest treat of a summer holiday if there were no flies, and no trout that appreciated them." The niche filled by the fly is therefore a very important one. It neither lives a useless life nor dies a useless death. Its sphere of usefulness is as striking and suggestive as the wondrous delicacy of its form and structure, and they both point us to the Great Creator whose greatness and goodness are manifested through all His works— "Who sees with equal eye, as God of all, A hero perish, or a sparrow fall."