Book of Joel Chapter 1 Vs. 6

 An Invasion of Locusts

For a nation is come up upon my land, strong, and without number, whose teeth are the teeth of a lion, and he hath the cheek teeth of a great lion. Joel 1:6

a nation is... The only nation that will come against Judah in the day of the Lord will be that of the future Antichrist from Syria and Babylon (Eze. 38-39; Dan. 11:41-45; 2Th. 2:3-4; Rev. 16:13-16; 19:11-21). His army of that day is called "the northern army" (Joel 2:20). A literal invasion of locusts pictured the kind of destruction and judgment inflicted by human armies.

The key word in this verse is “my”. Judah was His people. This nation could not come against God’s land, except God ordained it. God sent this vicious nation against His people and land.

Joel described these hostile, countless locusts as possessing the “fangs of a lioness,” so able were they to devour anything in their path. They are occasionally used as symbolic of violence (Gen. 49:9; Num. 23:24), and of the violent, awesome nature of God’s judgment (Isa. 30:6; Hos. 13:8).

The “teeth of a lion” speaks of the great destruction.

Pro. 30:14 “[There is] a generation, whose teeth [are as] swords, and their jaw teeth [as] knives, to devour the poor from off the earth, and the needy from [among] men.”

Like a mighty nation an innumerable (without number) swarm of locusts had invaded the prophet’s land. Their ability to devour was like that of a lion, which can rip and tear almost anything with its powerful teeth (likened to fangs).