Locusts

Locusts aren’t a type of animal. They are a condition some grasshoppers experience. Many species of grasshoppers become locusts when they are too crowded (literally their legs rubbing together triggers the change). Once grasshoppers start to swarm they will join up with others, physically grow larger, change color, and eat basically anything they find. Most of a swarm will be born as part of the swarm (increased mating is part of swarm behavior). This is why it often seems like locust swarms come out of nowhere. Add in the amount of calories they need to stay airborne, and in addition to devouring acres upon acres of crops, they also cannibalize each other in the air.