'Clouds' in the Bible

For if you do not let my people go, see, I will send clouds of flies on you and on your servants and on your people and into their houses; and the houses of the Egyptians and the land where they are will be full of flies.

And the Lord did so; and great clouds of flies came into the house of Pharaoh and into his servants' houses, and all the land of Egypt was made waste because of the flies.