Then the LORD said to Moses, “Say to Aaron, ‘Stretch out your staff and strike the dust of the earth, so that it may become gnats in all the land of Egypt.’”
16. And the Lord said unto Moses. In this place again, as before, Aaron is commanded to act as the inferior of Moses in punishing the tyrant; and this as being more ignominious than as if Moses alone had been employed. The nature of this third plague is very remarkable.
Here is a short account of the plague of lice. It does not appear that any warning was given of it before. Pharaoh's abuse of the respite granted to him might have been a sufficient warning to him to expect another plague: for if the removal of an affliction harden us, and so we lose the benefit of it, we may conclude it goes away...
Commenting on Exodus 8:16-19
And they did so,.... As follows: for Aaron stretched out his hand with his rod; as directed and ordered: and smote the dust of the earth, and it became lice in man and in beast; which shows it was a miraculous operation, since lice do not usually spring from dust, but thrive in the sweat of bodies, and the nastiness of them, through sloth and...