In Joel 1:10, 12, this signifies people who worship.

(References: Amos 5, 5:16; Apocalypse Explained 652)

The head is the part of us that is highest, which means in a representative sense that it is what is closest to the Lord. Because of this the head represents what is inmost in us, the thing at the center of our being. In most cases this means intelligence and wisdom, since most of us are in a state of life in which we are led by our thoughts and reason. In the case of the Lord, however, it often represents His perfect love. And in many cases the head is used to represent the whole person.

(References: Apocalypse Explained 577; Apocalypse Revealed 538, 823; Arcana Coelestia 7859, 9656, 10011)