Exodus 8:19 (KJV)

And they did so; for Aaron stretched out his hand with his rod, and smote the dust of the earth, and it became lice in man, and in beast; all the dust of the land became lice throughout all the land of Egypt.

And the magicians did so with their enchantments to bring forth lice, but they could not: so there were lice upon man, and upon beast.

Then the magicians said unto Pharaoh, This is the finger of God: and Pharaoh’s heart was hardened, and he hearkened not unto them; as the Lord had said.

And the Lord said unto Moses, Rise up early in the morning, and stand before Pharaoh; lo, he cometh forth to the water; and say unto him, Thus saith the Lord, Let my people go, that they may serve me.

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.