But why does the desert locust go gregarious, when the vast majority of grasshopper species remain solitarious? That might have something to do with the dry environments these species call home. Desert locusts only lay eggs in moist soil, to keep them from drying out. When heavy rains come in to saturate the desert, locusts—ever the opportunists—breed like mad and fill the soil with their eggs, perhaps 1,000 per square meter of soil. When those eggs hatch, they’ll have plenty of vegetation to eat, until things dry up once again.As soon as things start getting crowded, desert locusts become gregarious and migrate away in search of more food. “If they were to stay locally, one potential is that there are too many of them and they would run out of food,” says Cease. “And so they migrate to find better resources.” By doing so in swarms, the locusts find safety in numbers—any individual is less likely to get eaten. But for farmers in surrounding countries, the locusts’ newfound mobility can spell ruin.
To adapt to this new social life, the locusts’ bodies transform, inside and out. They change color from a drab tan to a striking yellow and black , perhaps a signal to their predators that they’re toxic. Indeed, while solitarious locusts avoid eating toxic plants, the gregarious locusts are actually attracted to the odor of hyoscyamine, a toxic alkaloid found in local plants. Sure, by eating those plants and assuming their toxicity and changing color to yellow and black, the insects make themselves more conspicuous, but that isn’t such a big deal when there’s millions of them barreling across a landscape—no one’s trying to hide. Being bright and alone, especially in a barren desert, probably isn’t a good strategy for the solo locust, so they stay drab.
And speaking of food, you might assume that to fuel their epic migrations—an individual locust might travel over 90 miles in a day, consuming its own weight in plant matter—the insects would need to load up on protein, especially since their new bodies come with extra muscle mass. To put it in human terms, says Rick Overson, research coordinator of the Global Locust Initiative, “If your friend told you that they were going to become a vegan, one concern you might have for them is to make sure to get enough protein.”
We’re Eating This Planet to Death