Charles Ellicott Commentary Joel 1:4

"That which the palmer-worm hath left hath the locust eaten; and that which the locust hath left hath the canker-worm eaten; and that which the canker-worm hath left hath the caterpillar eaten." — Joel 1:4 (ASV)

That which the palmerworm has left.— The picture is introduced suddenly and graphically. “Behold the desolation!” “Note the cause.” The earth is bared by locusts beyond all previous experience. There were different kinds of locusts; as many as ninety have been counted. The four names, palmerworm, locust, cankerworm, caterpiller, indicate different swarms of the insect. The first, Gazam, points to its voracity; the second, Arbeh, to its multitude; the third, Yelek, to its manner of “licking up” the grass like cattle; the fourth, Chasil, to its destructive effect.

The number enumerated, four, draws attention to the four sore judgments with which Ezekiel was instructed to threaten Jerusalem, and to the four foreign invasions by the Assyrians, Chaldeans, Macedonians, and Romans.