surface of the ground. The eggs are surrounded by foam and this hardens into a membrane and plugs the hole above the egg pod. The eggs absorb moisture from the surrounding soil. The incubation period before the eggs hatch may be two weeks, or much longer, depending on the temperature. The newly hatched nymph soon begins to feed, and if it is a gregarious individual, is attracted to other hoppers and they group together. As it grows, it needs to moult (shed its exoskeleton). Its hard cuticle splits and its body expands, while the new exoskeleton is still soft. The stages between moulting are called instars and the desert locust nymph undergoes five moults before becoming a winged adult. Immature and mature individuals in the gregarious phase form bands that feed, bask, and move as cohesive units, while solitary-phase individuals do not seek conspecifics. After the fifth moult, the insect is not yet mature. It is at first soft and pink with drooping wings, but over the course of a few days, the cuticle hardens and haemolymph is pumped into the wings, which stiffens them. Maturation can occur in 2–4 weeks when the food supply and weather conditions are suitable but may take as long as 6 months when they are less ideal. Males start maturing first and give off an odour that stimulates maturation in the females. On maturing, the insects turn yellow and the abdomens of the females start swelling with developing eggs. Ecology and swarming 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