Locust swarms don’t happen often. In fact, they occur only when the insects undergo a remarkable transformation. In small numbers, locusts are harmless, says Hojun Song, an entomologist, or insect scientist, at Texas A&M University. The bugs don’t move around much and mostly avoid one another. Scientists call this the locusts’ solitary phase (see Locust Life Cycle).
But when locust populations start to grow in response to changing conditions in their environment, like they did in the Arabian Desert in 2018, the insects go through a dramatic change. Their colors shift from dark green to bright yellow and black. The insects also group together and become more active. When a locust transforms, “It’s like the Hulk,” says Song. The insects enter a gregarious, or social, phase. They form swarms with a single purpose: finding food.