This is the fourth plague. There are different interpretations of this plague between some Jewish and other scholastic sources. What is interpreted as flies is rendered as wild animals from some Jewish traditions. We will hold the King James interpretation of flies. Thus fourth plague was a judgement of Uatchit, the god of flies. This god is the equivalent of Beelzebub, an ancient Philistine god of Ekron. The thing is that between the rest of Egypt and the land of Goshen, there was a division, so that Pharaoh will know this was God. These flies were a pointer to defilement and pollution of the land. They could corrupt everything they touch. Pharaoh was forced to call a truce, but did not end the hardness of the heart. God by this act kept raising the bar. Pharaoh had to bow, and he will. The one assigned over your situation must bow too. God is taking care of the different power bases. Soon , any Pharaoh(s) assigned to supervise your case will be broken by the very things they worship. God is raising the bar.
Else, if thou wilt not let my people go, behold, I will send swarms of flies upon thee, and upon thy servants, and upon thy people, and into thy houses: and the houses of the Egyptians shall be full of swarms of flies, and also the ground whereon they are. And I will sever in that day the land of Goshen, in which my people dwell, that no swarms of flies shall be there; to the end thou mayest know that I am the Lord in the midst of the earth. Exodus 8:21-22 KJV