וַיַּֽעֲשׂוּ־כֵ֗ן וַיֵּט֩ אַהֲרֹ֨ן אֶת־יָד֤וֹ בְמַטֵּ֙הוּ֙ וַיַּךְ֙ אֶת־עֲפַ֣ר הָאָ֔רֶץ וַתְּהִי֙ הַכִּנָּ֔ם בָּאָדָ֖ם וּבַבְּהֵמָ֑ה כָּל־עֲפַ֥ר הָאָ֛רֶץ הָיָ֥ה כִנִּ֖ים בְּכָל־אֶ֥רֶץ מִצְרָֽיִם׃
И они сделали это; и протянул Аарон руку свою жезлом и поразил прах земли, и на коме и звере были комары; вся пыль земли превратилась в комаров по всей земле Египетской.
Rashbam
דים, the letter ם at the end is an addition similar to ריק and ריקם. We explained this on Exodus 8,13 with the word כנם.
Rabbeinu Bahya
עולת שבת בשבתו, “the Sabbath burnt-offering on its Sabbath.” This means that the procedure is to take place on each Sabbath, as if the Torah had written דבר יום ביומו, “a daily procedure day by day” (Exodus 8,13).
על עולת התמיד, “in addition to (after) the daily total-offering.”
על עולת התמיד, “in addition to (after) the daily total-offering.”
Haamek Davar
And there were lice. The Torah repeats these words (from v.13) to inform that they settled on the bodies of people and animals and bit them in the manner of lice, which do not swarm but are attached to the body. This is implied by the Midrash Tanchuma: “They entered the Egyptians’ bodies like arrows”.