Wyjścia 8:20 Midrasz: Midrash Tanchuma & Shemot Rabbah

Our sages of blessed memory said: The Holy One, blessed be He, followed the military tactics employed by kings when inflicting the plagues upon them. When the people of a province rebel, a human king dispatches his legions to surround them. First he dams up their water supply. If the people repent, well and good; but if not, he orders thunderous noises to be directed against them. If they are contrite, good; but if not, he commands that arrows be shot at them. If they relent (their actions), well and good; but if not, he sends barbarians against them. If they retract, good; but if not, he orders other reprisals to be taken against them. If they are contrite, well and good; but if not, he orders naphtha to be hurled upon them. If they are repentant, good; but if not, he catapults stones upon them. If they repent, good; but if not, he turns a large population against them. If they retract, good; but if not, he imprisons them. If they relent, good; but if not, he destroys their leaders. The Holy One, blessed be He, attacked Egypt with the tactics employed by a king. The first thing He did was to cut off their water supply, as it is said: And he turned their rivers into blood. They were not contrite, and He therefore brought tumultuous noises upon them. These were the frogs. R. Yosé the son of Hanina said: Their croaking was harder to bear than the havoc they wrought. Still they did not repent, and so he shot arrows at them. These were the gnats, as it is said: And there were gnats upon man, and upon beast (Exod. 8:13). They penetrated the bodies of the Egyptians like spears. However, they did not become contrite, and so He sent barbarians against them. These were the swarms, as it is said: And there came grievous swarms of beasts (ibid., v. 20). Still they did not relent, and so He took other reprisals against them. He brought the murrain: And all the cattle of Egypt died (ibid. 9:6). Nevertheless, they did not repent, and so He poured naphtha over them. These were the boils, as it is said: And a boil breaking forth with blains upon man and upon beast (ibid., v. 9). Still they were not contrite, and so He catapulted projectiles upon them. This was the hail. But even then they did not repent, and so he stirred up a large population against them, that is, the locusts. Even so, they did not mend their ways, and so He imprisoned them. This was the darkness, as it is said: And there was a thick darkness (ibid. 10:22). When they refused to repent, He killed their important men, as it is said: The Lord smote all the firstborn (ibid. 12:19).

“The Lord did so; and heavy swarms came into the house of Pharaoh, and into the house of his servants; and throughout the land of Egypt the land was ruined due to the swarms” (Exodus 8:20).
“The Lord did so; and heavy swarms came into the house of Pharaoh” – he was afflicted first, as he began with the wicked counsel first, as it is stated: “Pharaoh commanded…” (Exodus 1:22), and then, “the house of his servants.”
“Pharaoh called for Moses and Aaron, and said: Go sacrifice to your God in the land. Moses said: It is not proper to do so, as we will sacrifice the abomination of the Egyptians to the Lord our God; behold, were we to sacrifice the abomination of the Egyptians before their eyes, would they not stone us?” (Exodus 8:21–22).
“Pharaoh called.… Moses said: It is not proper to do so” – because the Egyptians prostrate themselves to these animals as a god.
“We will go on a three-day journey into the wilderness, and sacrifice to the Lord our God, as He will command us” (Exodus 8:23).
“We will go on a three-day journey into the wilderness” – in order to mislead them.
“Pharaoh said: I will let you go, and you will sacrifice to the Lord your God in the wilderness; just do not go very far; entreat for me. Moses said: Behold, I am leaving you, and I will entreat the Lord, and the swarms will depart from Pharaoh, from his servants, and from his people, tomorrow; only let Pharaoh not continue to be deceitful by not letting the people go to sacrifice to the Lord” (Exodus 8:24–25).
“Pharaoh said: I will let you go.… Moses said: Behold, I am leaving you” – what is “behold”? The prayer will be immediate, so that the swarm will depart from you tomorrow. That is what is written: “The swarms will depart…[tomorrow].”
“Moses left Pharaoh, and entreated the Lord. The Lord did according to the word of Moses; and He removed the swarms from Pharaoh, from his servants, and from his people; not one remained” (Exodus 8:26–27).
“Moses left.… The Lord did according to the word of Moses; and He removed the swarms” – why did He bring swarms upon them? It is because they would say to Israel: ‘Go out and bring us bears, lions, and leopards,’ in order to torment them; therefore, He brought upon them swarms of beasts; this is the statement of Rabbi Yehuda. Rabbi Neḥemya said: [They were] species of hornets and mosquitoes. The statement of Rabbi Yehuda appears correct, as regarding the frogs it is written: "The frogs died” (Exodus 8:9), because there was no benefit from their skins; however, regarding the swarms there was [potential] benefit from their hides; therefore, “not one remained.” Had they been hornets or mosquitoes they could have been left to reek.