The main collective noun for Locust is a plague, a cloud, or a swarm. A plague of locusts is a large group of locusts that can cause extensive damage to crops and vegetation. A cloud of locusts is a large group of locusts that can darken the sky. A swarm of locusts is a large group of locusts that can move quickly and cover a large area.
The etymology of the collective nouns a plague, a cloud, and a swarm in relation to Locust is derived from the biblical story of the Ten Plagues of Egypt. In this story, a plague of locusts was sent to Egypt to punish the Pharaoh for not freeing the Israelites. The plague of locusts was so large that it darkened the sky, creating a cloud of locusts. The locusts moved quickly and covered a large area, creating a swarm of locusts.