In reading about these guys I found them described as both grasshoppers and locusts – so I went a researching.

It turns out that all locusts are grasshoppers, but not all grasshoppers are locusts. Certain grasshoppers, when conditions are right, will go into a swarming mode. This is often triggered by over-crowding. Interestingly, the over-crowding response is triggered by their hind legs being stimulated, which causes a release of serotonin (I believe in the brain, but the articles aren’t clear). This release causes the grasshoppers to change form, eat more, breed more quickly, and start to congregate into groups. Then they all fly away to devastate the land all around them.

That’s right, the grasshoppers’ genetic response to overcrowding is to eat all their food and make more grasshoppers.

I guess it works.