Prior to some of the other Makos, Moshe addressed Pharaoh in the name of "Hashem, G-d of the Ivrim" (7:16). Why is the Makah of Arov introduced by the Specific Name (Havayah)?
Maharal (Gevuros Hashem Ch. 32, p. 122): Makas Arov would make it clear that the Makos were not natural occurrences, but rather from Hashem alone. Wild animals will naturally spread out at will; but during this Makah they would not enter the Land of Goshen. This showed that Hashem is unique and distinct above everything else; He has no need to operate via the rules of nature. 1 To reflect this lesson, the warning was delivered with the name Havayah. 2
The Torah will emphasize this below, "... so that you will know, that I am Hashem in the midst of the earth!" (8:18).
See above regarding Makos Dam (7:17:1.1:1) and Tzefarde'a (7:26:152:1); and below regarding Barad (9:29:3:3 and its note) and Makas Bechoros (11:4:152:1).
Why do the Makos follow a set pattern? In the first out of each set of three Makos (such as this plague of Arov), Moshe confronted Pharaoh at the Nile; in the second, at the palace; whereas the third had no warning at all?
Refer to 7:14:8:2, regarding the Makos' breakup into the categories De'tzach, A'dash, Be'achav.
