English: ( a) Geographic distribution of the desert locust. During ‘recession’ periods, desert locusts are restricted to the semi-arid and arid regions of Africa, the Arabian Peninsula and South-West Asia that receive less than 200 mm of annual rain. The recession area covers about 16 million km 2 in 30 countries. Within this recession area, locusts move seasonally between winter/spring and summer breeding areas. During outbreaks, desert locusts may spill into more fertile adjacent regions, threatening an area of some 29 million km 2 comprising 60 countries as outbreaks escalate into upsurges and further into plagues. The recession breeding areas and migration patterns may have predictive value to understand how the swarms will migrate Range of the non-swarming southern sub-species S. gregaria flaviventris not shown. Figure based on information from FAO Locust Watch (Cressman, 2016; Symmons & Cressman, 2001), map derived from Google Map Data ©2020 Google. ( b) Phase polyphenism in desert locusts, using the example of sexually mature males. The gregarious male (right) is brightly coloured, while the solitarious male relies on camouflage colours. In this staged scene, the solitarious male was forced into close proximity of the gregarious male and is seen retreating from its conspecific. Photo by H. Verlinden and R. Verdonck.