Exodus 8:21-24

If 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. “ ‘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. I will make a distinction between my people and your people. This sign will occur tomorrow.’ ” And 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.