Jamieson, Fausset and Brown on Exodus 8:16

Ex 8:16-19. Plague of Lice.

16. smite the dust of the land, &c.--Aaron's rod, by the direction of Moses, who was commanded by God, was again raised, and the land was filled with gnats, mosquitoes--that is the proper meaning of the original term. In ordinary circumstances they embitter life in Eastern countries, and therefore the terrible nature of this infliction on Egypt may be imagined when no precautions could preserve from their painful sting. The very smallness and insignificance of these fierce insects made them a dreadful scourge. The magicians never attempted any imitation, and what neither the blood of the river nor the nuisance of the frogs had done, the visitation of this tiny enemy constrained them to acknowledge "this is the finger of God"--properly "gods," for they spoke as heathens.