Exodus 8:21

18 The magicians tried by their secret arts to produce gnats, but they could not. So there were gnats on man and beast. 19 Then the magicians said to Pharaoh, “This is the finger of God.” But Pharaoh’s heart was hardened, and he would not listen to them, as the Lord had said.

20 Then the Lord said to Moses, “Rise up early in the morning and present yourself to Pharaoh, as he goes out to the water, and say to him, ‘Thus says the Lord, “Let my people go, that they may serve me. 21 Or else, if you will not let my people go, behold, I will send swarms of flies on you and your servants and your people, and into your houses. And the houses of the Egyptians shall be filled with swarms of flies, and also the ground on which they stand. 22 But on that day I will set apart the land of Goshen, where my people dwell, so that no swarms of flies shall be there, that you may know that I am the Lord in the midst of the earth. 23 Thus I will put a division between my people and your people. Tomorrow this sign shall happen.”’” 24 And the Lord did so. There came great swarms of flies into the house of Pharaoh and into his servants’ houses. Throughout all the land of Egypt the land was ruined by the swarms of flies.