Exodus 8:20-24

And the LORD said to Moses, “Rise early in the morning and stand before Pharaoh as he comes out to the water. Then say to him, ‘Thus says the LORD: “Let My people go, that they may serve Me. Or else, if you will not let My people go, behold, I will send swarms of flies on you and your servants, on your people and into your houses. The houses of the Egyptians shall be full of swarms of flies, and also the ground on which they stand. And in that day I will set apart the land of Goshen, in which My people dwell, that no swarms of flies shall be there, in order that you may know that I am the LORD in the midst of the land. I will make a difference between My people and your people. Tomorrow this sign shall be.” ’ ” And the LORD did so. Thick swarms of flies came into the house of Pharaoh, into his servants’ houses, and into all the land of Egypt. The land was corrupted because of the swarms of flies.