That which the palmerworm hath left hath the locust eaten; and that which the locust hath left hath the cankerworm eaten; and that which the cankerworm hath left hath the caterpiller eaten. That which the palmerworm hath left - Here he begins to open his message, and the words he chooses show that he is going to announce a devastation of the land by locusts, and a famine consequent on their depredations. What the different insects may be which he specifies is not easy to determine. I shall give the words of the original, with their etymology.
The palmerworm, גזם gazam, from the same root, to cut short; probably the caterpillar, or some such blight, from its cutting the leaves of the trees into pieces for its nourishment.
The locust, ארבה arbeh, from רבה rabah, to multiply, from the immense increase and multitude of this insect.
Cankerworm, ילק yelek, from לק lak, to lick or lap with the tongue; the reference is uncertain.
Caterpillar, חסיל chasil, from חסל chasal, to consume, to eat up, the consumer. Bishop Newcome translates the first grasshopper; the second, locust; the third, devouring locust; and the fourth, consuming locust. After all that has been said by interpreters concerning these four animals, I am fully of opinion that the arbeh, or locust himself, is the gazam, the yelek, and the chasil and that these different names are used here by the prophet to point out the locust in its different states, or progress from embryo to full growth. See the note on Joel 2:2 (note).