Charles Ellicott Commentary Isaiah 33:4

"And your spoil shall be gathered as the caterpillar gathereth: as locusts leap shall men leap upon it." — Isaiah 33:4 (ASV)

Your spoil ... —The words are addressed to the invader. He who came to spoil should find himself spoiled. As caterpillars and locusts devour the green vegetation, so should he (or they, the indefinite pronoun standing for the people of Jerusalem) strip his camp of all its treasures.