A large group of locusts is called a plague of locusts. Alternatively, a large group of locusts can be referred to as a locust cloud or swarm of locusts.
A group of locusts is called a plague, while a group of grasshoppers is a cloud, according to the U.S. Geological Survey. The use of the term "cloud" to refer to locusts is probably due to the similarity between locusts and grasshoppers. "Cloud" can also refer to a group of gnats. A swarm is a large number of any insect, so it can be used interchangeably for anything from bees, wasps or ants.