Exodus 8:20-22

The Plague of Flies 20Then the LORD said to Moses, “Get up early in the morning and confront Pharaoh as he goes to the river and say to him, ‘This is what the LORD says: Let my people go, so that they may worship me.

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.