Albert Barnes Commentary Jeremiah 46:23

"They shall cut down her forest, saith Jehovah, though it cannot be searched; because they are more than the locusts, and are innumerable." — Jeremiah 46:23 (ASV)

Or, They have cut down her forest, says Yahweh, for it is impenetrable, that is, just as a pathless forest must be cleared to assist agriculture and the movement of people, so must the false worship and the material prosperity of Egypt be overthrown.

Grasshoppers - The invading host advances as multitudinous as the locusts which consume the whole vegetation of the land on which they alight.