Exodus 8:17-19

They did so; and Aaron stretched out his hand with his staff, and struck the dust of the earth, and there were gnats on man and beast. All the dust of the earth became gnats through all the land of Egypt. The magicians tried with their secret arts to bring forth gnats, but they could not; so there were gnats on man and beast. Then the magicians said to Pharaoh, “This is the finger of God.” But Pharaoh’s heart was hardened, and he did not listen to them, as the LORD had said.