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A field study of the food eaten by solitary desert locusts was carried out in a winter breeding area in Mauritania. The food eaten, determined by the plant epidermis found in fecal pellets, was compared to the plant’s availability in the habitat. Schouwia purpurea, well represented in the diets, was dominant at the study site. Adults had a preference for Tribulus terrester. Growth and feeding on these two plants were compared. The high water content of S. purpurea leaves limited the dry matter eaten and slowed down growth. Glucosinolates were separated and quantified by gas chromatography. There are 132-mu-mol/g dry matter in green leaves. In multiple choice tests, with paper disks, glucosinolate extracts were phagostimulant at a low concentration (21-mu-mol/g dry matter) and repulsive at a higher one (214-mu-mol/g dry matter). Biting behavior on S. purpurea was recorded and analyzed on video. The importance of Schouwia purpurea in desert locust habitats and its defenses is discussed.