Israel’s growing season had two main crops. The first was planted in autumn and harvested in the spring. The second was planted during the winter and harvested in early summer. For swarming locusts to come at this time would result in famine since that which was meant to provide for the people would now be taken.1
1 This is what the Lord GOD showed me: behold, he was forming locusts when the latter growth was just beginning to sprout, and behold, it was the latter growth after the king’s mowings.