(16) And the LORD said to Moses, “Early in the morning present yourself to Pharaoh, as he is coming out to the water, and say to him, ‘Thus says the LORD: Let My people go that they may worship Me. (17) For if you do not let My people go, I will let loose AROV against you and your courtiers and your people and your houses; the houses of the Egyptians, and the very ground they stand on, shall be filled with AROV. (18) But on that day I will set apart the region of Goshen, where My people dwell, so that no AROV shall be there, that you may know that I the LORD am in the midst of the land. (19) And I will make a distinction between My people and your people. Tomorrow this sign shall come to pass.’” (20) And the LORD did so. Heavy AROV invaded Pharaoh’s palace and the houses of his courtiers; throughout the country of Egypt the land was ruined because of the AROV.
לָמָּה הֵבִיא עֲלֵיהֶם עָרֹב, לְפִי שֶׁהָיוּ אוֹמְרִים לְיִשְׂרָאֵל צְאוּ וְהָבִיאוּ לָנוּ דֻּבִּים וַאֲרָיוֹת וּנְמֵרִים, כְּדִי לִהְיוֹת מְצֵרִים בָּהֶם, לְפִיכָךְ הֵבִיא עֲלֵיהֶם חַיּוֹת מְעֻרְבָּבוֹת, דִּבְרֵי רַבִּי יְהוּדָה.
רַבִּי נְחֶמְיָה אָמַר מִינֵי צְרָעִין וְיַתּוּשִׁין, וְנִרְאִין דְּבָרָיו שֶׁל רַבִּי יְהוּדָה, לְפִי שֶׁבַּצְּפַרְדְּעִים כְּתִיב (שמות ח, ט): וַיָּמֻתוּ הַצְפַרְדְּעִים, לְפִי שֶׁלֹא הָיָה בָּהֶן הֲנָאָה בְּעוֹרוֹתֵיהֶן, אֲבָל עָרֹב שֶׁהָיָה הֲנָאָה בְּעוֹרוֹתֵיהֶן, לְפִיכָךְ לֹא נִשְׁאַר בָּהֶן עַד אֶחָד, שֶׁאִלּוּ הָיוּ צְרָעִין וְיַתּוּשִׁין, הָיָה לָהֶן שֶׁיַּסְרִיחוּ.
"Why were AROV brought upon them? Since they were telling Israel, 'Go and bring us bears, lions, and leopards' in order to scare them. Therefore, God brought a mixture of wild animals," the words of Rabbi Yehudah.
Rabbi Nechemiah said, "They were species of annoying insects and midges."
And the words of Rabbi Yehudah are apparent, as it is written of the frogs, "and the frogs died" (Ex. 8:9), since they did not benefit from their skins. But there was a benefit from the skins of the AROV, therefore, none of them remained, for were there to have been insects and midges, they would have rotted.
את הערב. כָּל מִינֵי הַחַיּוֹת רָעוֹת וּנְחָשִׁים וְעַקְרַבִּים בְּעִרְבּוּבְיָא, וְהָיוּ מַשְׁחִיתִים בָּהֶם; וְיֵשׁ טַעַם בַּדָּבָר בָּאַגָּדָה בְּכָל מַכָּה וּמַכָּה לָמָּה זוֹ וְלָמָּה זוֹ; בְּטַכְסִיסֵי מִלְחֲמוֹת מְלָכִים בָּא עֲלֵיהֶם, כְּסֵדֶר מַלְכוּת כְּשֶׁצָּרָה עַל עִיר, בַּתְּחִלָּה מְקַלְקֵל מַעְיְנוֹתֶיהָ, וְאַחַר כָּךְ תּוֹקְעִין עֲלֵיהֶם וּמְרִיעִין בַּשּׁוֹפָרוֹת לְיָרְאָם וּלְבַהֲלָם, וְכֵן הַצְפַרְדְּעִים מְקַרְקְרִים וְהוֹמִים וְכוּ', כִּדְאִיתָא בְּמִדְרַשׁ רַבִּי תַּנְחוּמָא (פ' בא):
את הערב this means all kinds of wild beasts, serpents, and scorpions (a mixture [ערב] of noxious creatures) in a crowd (Exodus Rabbah 11:3) — these played havoc with them. There is a reason given in the Midrash in the case of each plague why this particular one and why that: God came against them with the tactics of warlike operations as carried out by kings in orderly sequence: a government (monarch) who is besieging a city first destroys its water supply, then they blow the trumpets and sound an alarm in order to terrify and dismay them — thus [their water supply was turned into blood], the frogs croaked and made a noise etc. - just as you will find it stated in the Midrash of Rabbi Tanchuma 2:3:4.
והערוב, I believe that the Torah describes different kinds of wolves that are called arov, since it is their way to hunt at night, as it is written, "The wolf of the desert ravages them" (Jeremiah 5:6), and it is written, "wolves of the steppe leave no bone until morning" (Tzefaniah 3:3). The fact that the wolf sets out when it gets dark, in the evening, and does not return until morning, is why this animal is referred to as ערוב, describing its habits.
וגם האדמה אשר הם עליה, a reference to the soil on which the houses stood which would become full of snakes and other creepers of the kind that inhabit the lower levels of the earth beneath its surface. The plague would result in the Egyptians feeling insecure in their homes even when they had shut every exit tightly.