What hath frogs wrought

The word צפרדע (frog, or, collectively, "frogs") is found in two places in Psalms. The order of the plagues dealt the Egyptians differs in Psalms from the recounting in Exodus. One traditional explanation for this (as suggested by the Radak, R. David Kimchi) is that the true order is represented in Exodus, so there's nothing lost by a change in the order in Psalms (which according to this understanding presumably differs for rhetorical reasons). The historical-critical explanation, not surprisingly, is that different traditions, or source texts, underlie the various recountings of the Exodus tale.

This all means that variances in Psalms (when compared to Exodus) should be looked at closely. In this week's parasha, here's how Egypt is affected by the frogs:

כז וְאִם-מָאֵן אַתָּה, לְשַׁלֵּחַ: הִנֵּה אָנֹכִי, נֹגֵף אֶת-כָּל-גְּבוּלְךָ--בַּצְפַרְדְּעִים.
Exodus 7:27 And if thou refuse to let them go, behold, I will smite all thy borders with frogs.
כח וְשָׁרַץ הַיְאֹר, צְפַרְדְּעִים, וְעָלוּ וּבָאוּ בְּבֵיתֶךָ, וּבַחֲדַר מִשְׁכָּבְךָ וְעַל-מִטָּתֶךָ; וּבְבֵית עֲבָדֶיךָ וּבְעַמֶּךָ, וּבְתַנּוּרֶיךָ וּבְמִשְׁאֲרוֹתֶיךָ.
28 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.
כט וּבְכָה וּבְעַמְּךָ, וּבְכָל-עֲבָדֶיךָ--יַעֲלוּ, הַצְפַרְדְּעִים.
29 And the frogs shall come up both upon thee, and upon thy people, and upon all thy servants.'

ב וַיֵּט אַהֲרֹן אֶת-יָדוֹ, עַל מֵימֵי מִצְרָיִם; וַתַּעַל, הַצְּפַרְדֵּעַ, וַתְּכַס, אֶת-אֶרֶץ מִצְרָיִם.
Exodus 8:2 And Aaron stretched out his hand over the waters of Egypt; and the frogs came up, and covered the land of Egypt.
ג וַיַּעֲשׂוּ-כֵן הַחַרְטֻמִּים, בְּלָטֵיהֶם; וַיַּעֲלוּ אֶת-הַצְפַרְדְּעִים, עַל-אֶרֶץ מִצְרָיִם.
3 And the magicians did in like manner with their secret arts, and brought up frogs upon the land of Egypt.
ד וַיִּקְרָא פַרְעֹה לְמֹשֶׁה וּלְאַהֲרֹן, וַיֹּאמֶר הַעְתִּירוּ אֶל-יְהוָה, וְיָסֵר הַצְפַרְדְּעִים, מִמֶּנִּי וּמֵעַמִּי; וַאֲשַׁלְּחָה, אֶת-הָעָם, וְיִזְבְּחוּ, לַיהוָה.
4 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.'

Let's compare Psalm 78:

מה יְשַׁלַּח בָּהֶם עָרֹב, וַיֹּאכְלֵם; וּצְפַרְדֵּעַ, וַתַּשְׁחִיתֵם.
45 He sent among them swarms of flies, which devoured them; and frogs, which destroyed them.

"Them" refers here to the Egyptians, I think.

The question is: which destruction is meant? The emphasis in Exodus is on the frogs' unstoppable fecundity, not on their destructive power. Rashi, commenting on the word "destroyed them" (ותשחיתם) in the verse in Psalms, says שומטין את ביציהם, "they [the frogs] took away their [the Egyptians'?] eggs." The reference is unclear to me, and I bet he's referring to a midrash I can't find right now. Perhaps Rashi is making an association with the root ש.ח.ת "destruction," which is known to Jews in the phrase השחתת זרע "[wanton] destruction of seed."

Perhaps it is the case (using a historical-critical approach) that the Psalmist knew of a different tradition, in which the frogs were not fecund but destructive. Rashi is combining their two effects, if I understand him correctly: since they were so multiplicative, they stole or took away the eggs of other creatures. Unfortunately, I'm still not clear on what Rashi means and whose eggs he's referring to. Any help here?