וגם את הצרעה, "and also the hornet,⁠" etc.; Remember that miracles occur on two levels, so-called "open" (supernatural) miracles, i.e. visible manifestations of God interfering with the laws of nature; secondly there are the so-called "hidden" miracles (natural) which are no less miraculous although we do not witness overt interference with the laws of nature. In the previous verse God referred to the first category of miracles, the ten plagues, etc., in which God demonstrated His mastery over the forces of the universe, the laws of nature.
Now the Torah, i.e. Moses, turns his attention to the occurrence of "hidden" miracles such as swarms of hornets which occur at regular intervals, almost like rain. Seeing that neither rainfall nor swarms of hornets are the result of changes in the laws of nature they are not regarded as miracles. This is why the Torah introduces this element with the word וגם, "and also,⁠" to say that in addition to the supernatural miracles mentioned above there will also be natural forces such as the hornet. The fact that God employs a tiny insect to drive out the powerful people of Canaan is surely enough of a miracle to register with the people who observe this. Therefore — לא תערוץ מפניהם, "You shall not be afraid of them (the inhabitants, not the hornets).⁠" The only One you shall be afraid of is the Lord your God Who dwells among you. (The author suggests reading the first 6 words in verse 21 together).

It is worth noting that the words ה' אלו-היך and the word בקרבך contain two separate praises of the Lord. They are the attributes גדול ונורא, "great and awesome.⁠" These two adjectives, i.e. attributes, refer to the two types of miracles we spoke of earlier. The word גדול describes the attribute involved when God performs "hidden" miracles, whereas the word נורא describes the attribute involved when He performs "open" miracles. When God's activities at the Sea of Reeds were reported in the Torah we read about נורא תהלות עושה פלא, "too awesome for praises, Doer of wonders" (Exodus 15,11). Presently (10,21) the Torah will refer to both kinds of miracles describing them under the heading of "את הגדולות ואת הנוראות האלה, "these awesome deeds and these great deeds.⁠" The צרעה is an insect similar to a fly which emits a poison by means of its sting. Our sages in Tanchuma Mishpatim 18 have said that a plague of such hornets occurred twice; once during the time of Moses and once during the life of Joshua. It would attack the enemies of the Israelites disabling them from offering serious resistance. The Israelites would simply kill the Canaanites without encountering resistance. There is another Midrash in Sotah 36 according to which the effect of the bite or sting of the hornet resulted in the victim becoming both blinded and impotent as if castrated. The prophet Amos 2,9 referred to this when he said: "Yet I destroyed the Emorite before them, whose stature was like the cedar's and who was as stout as an oak; destroying the boughs above and his trunk below.⁠" Onkelos also translates the word צרעה as ערעיתא, "wasp, hornet.⁠" According to Onkelos, the reason for this name may be that it encounters man like the Amalekites encountered the Israelites in the desert, i.e. אשר קרך בדרך (Deut. 25,18), compare Onkelos there.