New Defender's Study Bible Notes
1:4 palmerworm. It is probable that the four invaders mentioned here are all different species, or possibly different life stages, of the locust.
1:4 the locust. Much of Joel’s prophecy draws on the imagery suggested by a recent plague of locusts and other insects that had devastated the land of Judah. He uses these as a type of the ultimate “day of the LORD”—a phrase occurring five times in Joel’s prophecy.