'Locusts' signify falsities in the extremes, which consume the truths and goods of the church in a person. 'The locusts' which John the Baptist ate signify truths of a most common or general nature.
(References: Apocalypse Revealed 424, 430)
Joel 1:9-11
9
The meal offering and the drink offering are cut off from Yahweh's house. The priests, Yahweh's ministers, mourn.
10
The field is laid waste. The land mourns, for the grain is destroyed, The new wine has dried up, and the oil languishes.
11
Be confounded, you farmers! Wail, you vineyard keepers; for the wheat and for the barley; for the harvest of the field has perished.
