something in a very large number that swarms to a location, often causing destruction
—On the first day of the sale, the customers filled the store like a plague of locusts.

Because the pharaoh wouldn’t let the Israelites leave Egypt, God sent ten disasters, or “plagues,” on the Egyptians. The seventh plague was a terrible hail storm. The eighth was the “plague of locusts” (grasshoppers):

The Lord said to Moses, “Extend your hand over the land of Egypt for the locusts, that they may come up over the land of Egypt and eat everything that grows in the ground, everything that the hail has left.” So Moses extended his staff over the land of Egypt, and then the Lord brought an east wind on the land all that day and all night. The morning came, and the east wind had brought up the locusts! The locusts went up over all the land of Egypt and settled down in all the territory of Egypt. It was very severe; there had been no locusts like them before, nor will there be such ever again. They covered the surface of all the ground, so that the ground became dark with them, and they ate all the vegetation of the ground and all the fruit of the trees that the hail had left. Nothing green remained on the trees or on anything that grew in the fields throughout the whole land of Egypt. (Exodus 10:12-15)

Finally, God sent a tenth plague, in which an angel killed the first-born son in every Egyptian family. But the angel passed over the home of the Israelites, not harming them. Even now, this event is celebrated by Jewish people in the yearly Passover festival.

Following this last plague, the pharaoh told the Israelites to leave. But after they were gone, he changed his mind and chased them with his army.