Wyjścia 7:26 Midrasz: Shemot Rabbah & Sefer HaYashar (midrash)

“The Lord spoke to Moses: Come to Pharaoh, and say to him: So said the Lord: Let My people go, and they will worship Me. If you refuse to let them go, behold, I will smite all your borders with frogs” (Exodus 7:26–27).
“The Lord spoke to Moses: Come to Pharaoh.… If you refuse to let them go, behold, I will smite…” – that is what is written: “But the advantage of a land is in every way” (Ecclesiastes 5:8), and the entire midrash as it is written in Vayikra Rabba and in “This is the statute of the law” (Numbers 19:2):¹See Vayikra Rabba 22:2; Bemidbar Rabba 18:22. Our Rabbis say: “But the advantage of a land is in every way” – even items that you view as extraneous in the world, like flies, fleas, and mosquitos, they were included in the creation of the world, regarding which it is stated: “God saw everything that He had made [and behold, it was very good]” (Genesis 1:31).
Rabbi Aḥa son of Rabbi Ḥanina said: Even items that you view as extraneous in the world, like snakes and scorpions, they were included in the creation of the world. The Holy One blessed be He said to the prophets: ‘What do you think, that if you do not go on My mission I will have no emissary? “But the advantage of a land is in every way” – I will accomplish My mission even by means of a snake, or even by means of a scorpion, or even by means of a frog.’ Know that it is so, as were it not for the hornet, how would the Holy One blessed be He exact retribution against the Emorites,²See Sota 36a. and were it not for the frogs, how would He exact retribution from the Egyptians? That is what is written: “Behold, I will smite [all your borders with frogs].”

And at the end of two years the Lord sent Moses once more unto Pharaoh, to bring forth the ‎children of Israel and to send them away from the land of Egypt; and Moses came to the ‎house of Pharaoh and he spoke unto him according to the words of the Lord, but Pharaoh ‎would not hearken unto the voice of Jehovah, and the Lord concluded to show his might in ‎Egypt, on Pharaoh and his servants. And God smote Pharaoh and his people with very terrible ‎plagues, and he turned by the hands of Aaron all the waters of Egypt into blood, and when an ‎Egyptian came to drink and drew water and he looked into his pitcher, behold it was turned ‎into blood, and also when a woman kneaded her bread or cooked her meals, all had the ‎appearance of blood. And the Lord sent again, and he caused all the waters to produce frogs, ‎so that the frogs came into the houses of the Egyptians, and when the Egyptians drank the ‎water, their stomachs were filled with frogs, and they leaped within them like in the river. And ‎all the water they used for cooking and drinking turned into frogs, and when they lay upon ‎their beds, they perspired frogs from their body. But for all that the anger of the Lord did not ‎turn from them, and his hand was still out stretched upon all Egypt, to smite them with all the ‎terrible plagues; and he sent and turned their dust into lice, so that the ground of Egypt was ‎covered with lice two cubits in height. And the lice were also upon the flesh of man and beast ‎among all the people of Egypt, and also upon the king and the queen, and Egypt was greatly ‎afflicted on account of the lice. But for all that the anger of the Lord did not turn, and his hand ‎was still outstretched over Egypt, and the Lord sent all the beasts of the field, and they came ‎and destroyed man and beast, and the trees, and all that was in Egypt. Then the Lord sent fiery ‎serpents, and scorpions, and mice, and rats, and weasels, and other vermin, that creepeth in ‎the dust, as also flies and fleas and all sorts of insects, and they came and tortured the ‎Egyptians, entering even their eyes and their ears. Then the hornets came over them also, and ‎they drove them to hide in their innermost chambers, and the Egyptians had to hide ‎themselves from the swarms of vermin and they locked the doors after them. But the Lord ‎commanded the Tulzoth, the great monster of the sea to come up and invade Egypt; and she ‎had very long arms, ten cubits in length according to the cubits of a man, and she went up and ‎unroofed their houses, and she put forth her arms into the houses and removed the bolts and ‎bars and opened the houses of the Egyptians, and the swarm of animals filled the houses of ‎the Egyptians, to torture them exceedingly.‎