What is the significance of the hornet?
Rashi and Ramban #1 (citing the Tanchuma): The hornet, which did not cross the Yarden, 1 shot poison into the eyes of the three nations listed in the Pasuk and killed them.
Ramban #2: Hashem filled the air of their land with hornets 2 and it became dark, thereby preventing the Cana'anim from going to fight with Yisrael.
Sotah, 36a #1 (citing Resh Lakish): The hornet did not cross the Yarden with Yisrael. 3 It 'stood' on the bank of the Yarden and and shot poison at the enemy, blinding them above, and castrating them below. 4
Sotah, 36a #2 (citing Rav Papa): There were two lots of hornets; one in the days of Moshe, the other, in the days of Yehoshua.
Accorrding to the Ramban, this hornet (as opposed to the hornet in the time of Moshe) did cross the Yarden, as the Pasuk records in Yehoshua (24:11-12). See answer #2, and see Torah Temimah, citing Sotah, 36a and note 164.
Ramban: Like He did with the locusts in Egypt and in the days of Yo'el (Yo'el, 2:25).
See Torah Temimah. Oznayim la'Torah: The eyes and the Ervah - Midah ke'Neged Midah, because they sinned in the area of Arayos, as the Torah states in Acharei-Mos, 18:27, a sin that begins with the eyes. See Oznayim la'Torah, who elaborates and offers an additional explanation..
Why specifically the Chivi, the Cana'ani and the Chiti?
Rashi: The Chiti and Cana'ani were in Ever ha'Yarden. Even though the Chivi were situated west of the Yarden, and the hornet did not cross the Yarden, it shot poison at them from the other side. 1
Ramban #1: These three are only examples, whereas in fact, the hornet attacked all seven nations.
Ramban #2: Most men of these three nations opted to remain safely in their fortified cities and not to go and fight Yisrael. So Hashem sent the hornet to destroy them in their hoMeis. 2
Oznayim la'Torah: Because these three nations sinned in the area of adultery more thann the other nations of Cana'an. 3
See Oznayim la'Torah, who queries Rashi on a number of points. See also Torah Temimah, note 164, who switches 'Chiti' and 'Chivi' in the text of Rashi.
In the same way as He sent the locusts into the houses of the Egyptians, as the Torah writes in Bo, Sh'mos 10:6. See also Oznayim la'Torah.
Refer to 23:28:1:3*. See Oznayim la'Torah, who elaborates.
How will the hornets drive the nations out of the land?
Rashi and Ramban #1: They will strike their eyes, and inject poison and kill them.
Ramban #2: Because a. They will cover the land and cause it to go dark, 1 thereby rendering them incapable of going to fight Yisrael, and b. They will devour all the produce of the land. 2 .
See Sh'mos 10:15.
As the Pasuk writes [about the locusts] in the K'lalos in Ki Savo Devarim, 28:38 & 42.
QUESTIONS ON RASHI
Rashi writes that the Chiti and Cana'ani were in Eiver ha'Yarden (on the east side). But the Navi writes in Yehoshua 9:1 that all six Cana'ani nations were on the same (west) side of the Yarden?
Emes le'Ya'akov: They were actually on the west side of the Yarden, and Sichon and Og conquered them.
