Having said that a west wind blew the locusts into the Yam-Suf, why does the Torah add that not one locust remained?
Rashi: To teach us that the wind removed even 1 the locusts that the Egyptians had salted, from their jars. 2
Ramban (to 10:14, citing R. Chananel): We learn from here that from that time on, not one locust ever entered Egypt. 3
Gur Aryeh: This is implied by the extra term "one" (Echad); even that which they had set aside (Meyuchad) for their use - disappeared.
Oznayim la'Torah (citing the Tevu'os Shor, citing the Ma'ayan Ganim): The live locusts that remained actually lifted the pickled ones from the jars and carried them away with them.
Ramban (ibid.): And if it did, it did not do any harm there. On the other hand, following the plague of Tzefarde'a (which R. Chananel translates as crocodiles), the crocodiles remained in the River Nile, where they reside to this day, as the Pasuk states in Va'era (see 8:5). And it is with regard to these miracles such as these that the Pasuk writes, "Speak of all His wonders!" (Tehilim 105:2).
Seeing as a regular east wind brought the locusts, why did it require a strong west wind to remove them?
Oznayim la'Torah #1: The Gemara in Avodah Zarah 55a explains that when Hashem sends suffering on a person, He issues it with a Shevu'ah as to which date it will depart. Consequently, when Moshe Davened for the removal of the Arbeh before the given date, it required a strong wind to remove them. 1
Oznayim la'Torah #2: In contrast to the other winds, the east wind is intrinsically powerful, as the Gemara states in Gitin 31b.
Oznayim la'Torah #3: To bring the locusts, the east wind blew gently all night, to give a chance to Pharaoh to do Teshuvah; whereas a strong west wind was required to remove the locusts as quickly as possible, in accordance with Pharaoh's request.
Oznayim la'Torah #4: To bring the locusts, a regular east wind sufficed, since the locusts were hungry and thin. But to remove the satiated locusts which had become fat and heavy, required a strong west wind.
Oznayim la'Torah #5 (citing his nephew, R Valkin of Brooklyn): A strong wind was required to remove the locusts that the Egyptians had salted from their jars. 2
Oznayim la'Torah #6: A strong wind was required according to the explanation of the Ma'ayan Ganim - Refer to 10:19:1:1**.
Rashi (in some editions) comments at this point that "Ru'ach ha'Kadim" (in 10:13) meant 'an east wind;' and Rashi discusses Egypt's geographical location. Why wait until here to explain this?
Gur Aryeh #1: According to those editions, 1 Rashi is explaining why an east wind brought the Arbeh, and then a west wind drove them away.
Gur Aryeh #2: We know that the east wind is the strongest of the winds (Rashi to 14:21). Thus, it is not surprising that although an east wind was needed to displace the Arbeh from their point of origin to Egypt, the weaker west wind was sufficient to drive them back to their place. 2 But now that Rashi has told us that even the dead and preserved locusts were blown away, it would seem that the strong east wind would be needed at the Makah's conclusion as well! Rashi therefore chooses this point to explain the geographical location of Egypt.
Gur Aryeh: In those texts, Rashi first completes the comments relevant to our Pasuk (i.e. that not one preserved locust remained), before returning to discuss Pasuk 10:13. (In our editions of Rashi, however, the discussion appears in its proper place, to 10:13).
Why does the Torah not record that the wild beasts and the locusts died, as it did by the frogs?
Hadar Zekenim #1: Because, since Hashem created the frogs specifically for the plague, when the plague terminated, the frogs died. 1 On the other hand, He brought the wild beasts and the locusts from other locations. Consequently, once they had served their purpose, He returned them back to their places. Also, so the Egyptians should not benefit from the meat and skins of the Arov [or the flesh of the Arbeh].
Hadar Zekenim #2: Hashem removed the wild beasts and the locusts rather than allow them to die, so that the Egyptians should not derive benefit from the pickled locusts and from the skins of the wild animals - as opposed to the frogs which stank, causing the Egyptians to suffer even after the plague had terminated.
Presumably, the same applies to the lice.
