Opinions may differ as to whether the prophet means that the four swarms succeeded each other in the course of one year or over a longer period of successive years. The first is, in my view, the most obvious. The fact that Joel 2:25 mentions the years
need not be in conflict with this: after all, it may have happened that, in more than one year, one swarm followed the other (within each year).1
4 What the cutting locust left, the swarming locust has eaten. What the swarming locust left, the hopping locust has eaten, and what the hopping locust left, the destroying locust has eaten.