Exodus 8:21-24

21If you do not let my people go, I will send swarms of flies on you and your officials, on your people and into your houses. The houses of the Egyptians will be full of flies; even the ground will be covered with them.

22“ ‘But on that day I will deal differently with the land of Goshen, where my people live; no swarms of flies will be there, so that you will know that I, the Lord, am in this land.

23I will make a distinction between my people and your people. This sign will occur tomorrow.’ ”

24And the Lord did this. Dense swarms of flies poured into Pharaoh’s palace and into the houses of his officials; throughout Egypt the land was ruined by the flies.