Midrash Rabba Shemot parasha 10:וַתַּעַל הַצְּפַרְדֵּעַ וַתְּכַס אֶת וגו' תני רבי עקיבא אומר צפרדע אחת היתה והיא
השריצה ומלאה את ארץ מצרים אמר לו רבי אלעזר בן עזריה עקיבא מה לך אצל הגדה כלה מדברותיך ולך אצל נגעים ואהלות צפרדע אחת היתה ושרקה להן ובאו.
Shemot 7:27-28וְאִם-מָאֵן אַתָּה, לְשַׁלֵּחַ: הִנֵּה אָנֹכִי, נֹגֵף אֶת-כָּל-גְּבוּלְךָ--בַּצְפַרְדְּעִים."And if thou refuse to let them go, behold, I will smite all thy borders with frogs.
וְשָׁרַץ הַיְאֹר, צְפַרְדְּעִים, וְעָלוּ וּבָאוּ בְּבֵיתֶךָ, וּבַחֲדַר מִשְׁכָּבְךָ וְעַל-מִטָּתֶךָ; וּבְבֵית עֲבָדֶיךָ וּבְעַמֶּךָ, וּבְתַנּוּרֶיךָ וּבְמִשְׁאֲרוֹתֶיךָ
And the river shall swarm with frogs, which shall go up and come into thy house, and into thy bed-chamber, and upon thy bed, and into the house of thy servants, and upon thy people, and into thine ovens, and into thy kneading-troughs."
Shemot 8:2-4:On a peshat level, it is easy to say that the singular הַצְּפַרְדֵּעַ is a collective noun to refer to all the frogs, and that there are other Biblical instances of the same. But on a midrashic level, it is fitting to note the distinction and draw something from it.'And the frog[s] came up, and (it) covered, etc'. A brayta (See Sanhedrin page 67): R Akiva says, a single frog there was and she multiplied and filled the land of Egypt.וַיֵּט אַהֲרֹן אֶת-יָדוֹ, עַל מֵימֵי מִצְרָיִם; וַתַּעַל, הַצְּפַרְדֵּעַ, וַתְּכַס, אֶת-אֶרֶץ מִצְרָיִם."And Aaron stretched out his hand over the waters of Egypt; and the frogs came up, and covered the land of Egypt.
וַיַּעֲשׂוּ-כֵן הַחַרְטֻמִּים, בְּלָטֵיהֶם; וַיַּעֲלוּ אֶת-הַצְפַרְדְּעִים, עַל-אֶרֶץ מִצְרָיִם.
וַיִּקְרָא פַרְעֹה לְמֹשֶׁה וּלְאַהֲרֹן, וַיֹּאמֶר הַעְתִּירוּ אֶל-יְהוָה, וְיָסֵר הַצְפַרְדְּעִים, מִמֶּנִּי וּמֵעַמִּי; וַאֲשַׁלְּחָה, אֶת-הָעָם, וְיִזְבְּחוּ, ה.
And the magicians did in like manner with their secret arts, and brought up frogs upon the land of Egypt.
Then Pharaoh called for Moses and Aaron, and said: 'Entreat the LORD, that He take away the frogs from me, and from my people; and I will let the people go, that they may sacrifice unto the LORD.'"
Rabbi Elazar ben Azarya said to him, Akiva, what have you to do with Haggada? End your words and go to (the Laws) of (the impurities) of Skin Ailments and Tents. (Rather,) there was a single frog and she whistled* to them and they came.
Tanchuma Vaera, 14:כתוב אחד אומר וְשָׁרַץ הַיְאֹר, צְפַרְדְּעִים, וכתוב אחד אומר וַתַּעַל הַצְּפַרְדֵּעַ. רבי עקיבא אומר, צפרדע אחת היתה, והיו המצרים מכין אותה ומתזת צפרדעים הרבה.
One verse states 'And the river shall swarm with frogs' and the other verse states, 'And the frog(s) came up.' Rabbi Akiva says, it was a single frog, and the Egyptians hit it, and it spit out many frogs.
In terms of textual derivation of "whistled," I did mention a possible one:
Well, the verb is שרקה, whistled. I would claim there is a drash from Sharatz, with the emphatic Tzadi switching with the emphatic Kuf. R Akiva says צפרדע אחת היתה והיא השריצה, there was one frog and she hishritza, multiplied. R Elazar ben Azarya says צפרדע אחת היתה ושרקה להן ובאו, there was one frog and she sharqa, whisted. This would be based on the earlier pasuk, in which Moshe promised: וְשָׁרַץ הַיְאֹר, צְפַרְדְּעִים, וְעָלוּ וּבָאוּ בְּבֵיתֶךָ.I'm not sure of the textual basis of the Egyptians striking the frog is, or if one exists. However, what I'd like to cover here is why Rabbi Akiva and Rabbi Eliezer arrived at there particular reasons for the frog multiplying, on a thematic level.
To my mind, the fertility represented by frogs (as mentioned earlier, Heqet, the Egyptian's frog deity, was the goddess of fertility -- but this is not even necessary, as there is enough in the Torah's narrative itself) is supposed to parallel the Egyptians attitude towards the Israelites, who they felt were overrunning Egypt. As we read in the first perek of Shemot:
For Rabbi Akiva, the parallel is to the Egyptian oppression of the Israelites. Thus:
|יב וְכַאֲשֶׁר יְעַנּוּ אֹתוֹ, כֵּן יִרְבֶּה וְכֵן יִפְרֹץ; וַיָּקֻצוּ, מִפְּנֵי בְּנֵי יִשְׂרָאֵל.||12 But the more they afflicted them, the more they multiplied and the more they spread abroad. And they were adread because of the children of Israel.|
Rabbi Eliezer takes a different parallel. Besides the derivation of sharatz/ sharak, I believe that he considers the first frog to be Yosef. Yosef gained a foothold in Egypt. But then, he "whistled," and his relatives came from Canaan to overrun Egypt. Perhaps this too, can be read into the first perek of Shemot, which starts with Yosef and the 70 souls who came there, and leads to the attitude that the Israelites are too many.
midrashim literally, historically, as well? Perhaps, and perhaps not. Perhaps since Hashem works via middah kineged middah so as to send messages with His punishments, this was a way of doing so. Or perhaps the midrash is just an effective way to convey the deeper theme, but they actually held that a multitude of frogs historically came up from the river.