Radak: The enemy will consume your fortresses. Malbim - this will happen while you are trampling mud to strengthen your fortresses!

Radak: Just like locusts eat the grain until it is finished.

Rashi #1: Destruction with a broom locusts finish off all vegetation of the field.

Rashi #2: You will be covered with troops like locusts. Hiskaved is like "Am Kaved" (Bamidbar 20:20).

Radak: This is sweeping, like 'we are Mechabed between the beds' (Beitzah 2:7), Machbedos of a palm tree (Shabbos 124b). Yelek and Arbeh sweep the field [clean] of grain.

Malbim: Yelek is a kind of locust that comes out as a worm, and becomes wrapped in a covering. It stays there for a fixed time, and afterwards leaves with wings. The multitudes of merchants and nations found in Ninveh are like a Yelek that is still a worm that creeps on the ground. After Ninveh was captured, they left the covering and became a flying locust. You, Ninveh, hoped Lehiskaved k'Yelek (that the merchants will remain in you), but Hiskavdi k'Arbeh (they will fly away soon).

Radak: Hiskaved is Makor (like a gerund); Hiskavdi is a command, to Ninveh. What will it help if you increased Am Kaved (a numerous nation) - they will not help or save!

Radak citing Targum Yonasan: They will cover you like Yelek, and Yachselonayich ¹ like locusts.