Desert locusts have a solitary phase and a gregarious phase, a type of polyphenism. Solitary locusts nymphs and adults can behave gregariously within a few hours of being placed in a crowded situation, while gregarious locusts need one or more generations to become solitary when reared in isolation. Differences in morphology and behaviour are seen between the two phases. In the solitary phase, the hoppers do not group together into bands, but move about independently. Their colouring in the later instars tends to be greenish or brownish to match the colour of their surrounding vegetation. The adults fly at night and are also coloured so as to blend into their surroundings, the immature adults being grey or beige and the mature adults being a pale yellowish colour. In the gregarious phase, the hoppers bunch together and in the later instars develop a bold colouring with black markings on a yellow background. The immatures are pink and the mature adults are bright yellow and fly during the day in dense swarms.