The dromedary (Camelus dromedarius), also known as the dromedary camel, Arabian camel, or one-humped camel, is a large even-toed ungulate, of the genus Camelus, with one hump on its back. The dromedary is diurnal (active mainly during daylight); free-ranging herds feed and roam throughout the day, though they rest during the hottest hours around noon. The night is mainly spent resting. Dromedaries form cohesive groups of about 20 individuals, which consist of several females led by a dominant male. Females may also lead in turns. The dromedary's diet consists mostly of foliage, dry grasses and desert vegetation – mostly thorny plants. The dromedary is specially adapted to its desert habitat; these adaptations are aimed at conserving water and regulating body temperature. The bushy eyebrows and the double row of eyelashes prevent sand and dust from entering the eyes during strong windstorms, and shield them from the sun's glare. The hump stores up to 80 lb of fat, which the camel can break down into energy to meet its needs when resources are scarce.