Exodus 8:17-19

They did this, and when Aaron raised the walking stick that was in his hand and struck the dust on the ground, everywhere in Egypt the dust changed into gnats. The gnats got on the people and animals. Using their tricks, the magicians tried to do the same thing, but they could not make the dust change into gnats. The gnats remained on the people and animals. So the magicians told the king that the power of God had done this. But the king was stubborn and refused to listen to them, just as the LORD had said.