Exodus 8:20-24

20Then the Lord said to Moses, ‘Get up early in the morning. Meet Pharaoh when he goes out to the river. Then say to him, “The Lord says: You must let my people go. Let them go to worship me.

21If you do not let my people go, I will send thousands of flies on you. I will send them on your servants and on your people. I will send them into your houses. The houses of the Egyptians will be full of flies. The flies will cover all the ground where people live.

22But it will be different in the region of Goshen, where my people live. I will not send flies there. Then you will know that I, the Lord, am doing my work here in this land.

23I will make a difference between my people and your people. This miracle will happen tomorrow.” ’

24That is what the Lord did. Great numbers of flies came into Pharaoh's house and into his servants' houses. The flies went all over Egypt and they destroyed the whole land.