John Gill Commentary Judges 7:12

"And the Midianites and the Amalekites and all the children of the east lay along in the valley like locusts for multitude; and their camels were without number, as the sand which is upon the sea-shore for multitude." — Judges 7:12 (ASV)

And the Midianites and the Amalekites, and the children of the
east
The Arabians, who with the Amalekites joined the Midianites in this expedition:

lay along in the valley
in the valley of Jezreel, in their tents, which overspread the valley, or at least great part of it:

like grasshoppers for multitude ;
or locusts, which usually come in great numbers, and cover the air and the sun where they fly, and the earth where they light, as they did the land of Egypt; this army consisted at least of 135,000 men, as is clear from (Judges 8:10)

and their camels were without number; as the sand is by the sea side
for multitude ;
an hyperbolical expression, setting forth the great number of them which the countries of Midian and Arabia abounded with; and were very proper to bring with them, to load and carry off the booty they came for, the fruits of the earth; see (Judges 6:4Judges 6:5) .