Exodus 8:23

The fourth plague was the plague of flies. The Egyptians worshiped insects such as flies that seemed to be able to turn death into life, as their young seemed to emerge from decaying matter. If the Egyptians thought that insects had the secret of life, God would let them have all the insects they wanted. Some say that this infestation was the natural result of all the dead frogs, but there were no flies in Goshen (8:22), the northeastern delta area where the Hebrews lived. God’s miraculous power was clearly seen in his ability to infest one area while sparing another at will.