Locusts differ from other grasshoppers in their ability to change from a solitary living form into gregarious, highly mobile, adult swarms and hopper bands, as their numbers and densities increase. They exist in different states known as recessions (with low and intermediate numbers), rising to outbreaks, and extremely high densities or plagues. They have two to five generations per year. The desert locust risk increases with one-to-two-year continuum of favourable weather (greater frequency of rains) and habitats that support population increases leading to upsurges and plagues.