Exodus 8:31
And the LORD did according to the word of Moses; and he removed the swarms of flies from Pharaoh, from his servants, and from his people; there remained not one. And the LORD did according to the word of Moses; and he removed the swarms of flies from Pharaoh, from his servants, and from his people; there remained not one.
While under chastening Pharaoh promised to let Israel go three days' journey into the wilderness to sacrifice, and he asked Moses to pray for him. Moses warned him not to deal deceitfully by withholding permission to go after relief came. The Lord acted according to Moses' word and intercessory prayer and completely removed the swarms of flies from Pharaoh, from his servants, and from his people, so that not one remained. The removal extended even to their houses, leaving none behind. The complete removal showed that the fly-god could not protect Egypt or end the plague, so the Egyptians had to look elsewhere for relief. Once relieved, Pharaoh broke his word, hardened his heart again, and refused to let the people go.