Why does it say "ha'Nemalim Am Lo Az"?
Rashi (31): This refers to Bavel - "Hen Eretz Kasdim Zeh ha'Am Lo Hayah" (Yeshayah 23:13).
What is the significance of ants preparing food in summer?
Rashi (31, from Sanhedrin 96a): Nebuchadnetzar did one act for Hashem's honor. Bal'adan sent letters to Chizkiyah. He wrote 'Shalom to Melech Chizkiyah, Shalom to Yerushalayim, Shalom to the great G-d.' Nebuchadnetzar, Bal'adan's usual scribe, was away. When he heard, he said 'you call Him the great G-d, and you put Him at the end?!' He ran and recalled the letter 1 . Due to this, he merited kingship. He prepared his food in the summer 2 , like an ant.
Malbim (Derech ha'Muskal): An ant eats one and a half seeds in its life. Hashem put in their nature to prepare their food in the summer. They gather storehouses of food that they do not need at all. This is for people to learn this Midah - to gather Chachmah, and not rest their entire lives from gathering the laws of Chachmah. They should be. This is the opposite of a Naval who is satiated with food (22). He is Chacham b'Einav; he thinks that he already gathered to his Nefesh more than enough laws of Chachmah.
