Then the Lord told Moses, “Get up early in the morning and stand in Pharaoh’s way as he goes down to the river. Say to him, ‘This is what the Lord says: Let My people go, so they can worship Me. If you refuse, then I will send swarms of flies on you , your officials, you people, and all your houses. The Egyptian homes wil be filled with flies, and the ground will be covered by them. But this time I will spare the region of Goshen, where My people live. No flies will be found there. Then you will know that I am the Lord and that I am present even in the heart of your land. I will make a clear distinction between My people and your people. This miraculous sign will happen tomorrow.'” (vv. 20-23, NLT)
So Moses left Pharaoh’s palace and pleaded with the Lord to remove all the flies. And the Lord did as Moses asked and caused the swarms of flies to disappear from Pharaoh, his officials, and his people. Not a single fly remained. But Pharaoh again became stubborn and refused to let the people go. (vv. 30-32, NLT)