The Exodus writer began his tales of the confrontation between Aaron and Moses and the sorcerer’s of Egypt with a tit-for-tat theme. Whatever amazing feat Aaron would perform with his rod; Pharaoh would order his sorcerers to do the same, even when it meant increasing the pollutions of blood and frogs throughout all the land of Egypt. After the second plague, however, the sorcerers were stumped and had to give up. Aaron had caused "all the dust" in Egypt to become lice (or gnats or mosquitoes, depending on the translation), but somehow the sorcerers who had managed to change water that didn't exist into blood were unable to change dust that no longer existed into lice (or gnats or mosquitoes).
Exodus 8:16 Then Yahweh said to Moses, "Say to Aaron, 'Stretch out your staff and strike the dust of the earth, so that it may become gnats [lice] throughout the whole land of Egypt.'" 17 And they did so; Aaron stretched out his hand with his staff and struck the dust of the earth, and gnats [lice] came on humans and animals alike; all the dust of the earth turned into gnats [lice] throughout the whole land of Egypt. 18 The magicians tried to produce gnats [lice] by their secret arts, but they could not. There were gnats [lice] on both humans and animals. 19 And the magicians said to Pharaoh, "This is the finger of God!"