The book of Joel is known for its use of locusts as a metaphor for coming judgment. Many of us in the Western world have little personal experience with locusts or locust plagues. And I have always wondered what the difference was between grasshoppers and locusts. An article by Harold Brodsky helps to explain.
The mature biblical desert locust has a wingspan of about 4 inches, and a body length of about 3 inches. Locusts look like large grasshoppers and are, in almost all respects, morphologically the same. Technically, what distinguishes a true locust from a large grasshopper is behavior. When conditions are right, grasshoppers that normally act as solitary individuals learn to swarm. During daylight hours they will rise as a cloud and migrate in search of moist green vegetation. Not all species of grasshoppers can exhibit this type of behavioral transformation. When they do, they can be called locusts.Harold Brodsky, “An Enormous Horde Arrayed for Battle”: Locusts in the Book of Joel,” Bible Review 6:4 (1990): 24.