14 Therefore, let no one deceive you, when perchance you suffer annoyance from flies. For some have been mocked by the devil, and taken with flies. As fowlers are accustomed to put flies in their traps to deceive hungry birds, so these have been deceived with flies by the devil. Some one or other was suffering annoyance from flies; a Manichæan found him in his trouble, and when he said that he could not bear flies, and hated them exceedingly, immediately the Manichæan said, “Who made them?”
And since he was suffering from annoyance, and hated them, he dared not say, “God made them,” though he was a Catholic. The other immediately added, “If God did not make them, who made them?” “Truly,” replied the Catholic, “I believe the devil made them.” And the other immediately said, “If the devil made the fly, as I see you allow, because you understand the matter well, who made the bee, which is a little larger than the fly?” The Catholic dared not say that God made the bee and not the fly, for the case was much the same.
From the bee he led him to the locust; from the locust to the lizard; from the lizard to the bird; from the bird to the sheep; from the sheep to the cow; from that to the elephant, and at last to man; and persuaded a man that man was not made by God. Thus the miserable man, being troubled with the flies, became himself a fly, and the property of the devil. In fact, Beelzebub, they say, means “Prince of flies;” and of these it is written, “Dying flies deprive the ointment of its sweetness.”
Source: Tractates on the Gospel of John (New Advent)