Exodus 8:21 in the King James Version
Else, if thou wilt not let my people go, behold, I will send swarms of flies upon thee, and upon thy servants, and upon thy people, and into thy houses: and the houses of the Egyptians shall be full of swarms of flies, and also the ground whereon they are.
Context
20 The LORD said to Moses, “Rise up early in the morning, and stand before Pharaoh; behold, he comes out to the water; and tell him, ‘This is what the LORD says, “Let my people go, that they may serve me.
21 Else, if you will not let my people go, behold, I will send swarms of flies on you, and on your servants, and on your people, and into your houses. The houses of the Egyptians shall be full of swarms of flies, and also the ground they are on.
22 I will set apart in that day the land of Goshen, in which my people dwell, that no swarms of flies shall be there, to the end you may know that I am the LORD on the earth.