Colias, or clouded yellow butterflies, is a genus of butterflies in the family Pieridae. They are often called clouded yellows; the North American name "sulphurs" is elsewhere used for Coliadinae in general. The closest living relative is the genus Zerene, which is sometimes included in Colias. This genus occurs throughout the Holarctic, including the arctic regions. They are also found in South America, Africa, China and India. Their caterpillars feed on certain Fabaceae, for example vetches (Vicia). While most are thus beneficial by keeping weeds at bay, some occasionally become nuisance pests on crops like alfalfa. In some species, the wings of males have brilliant ultraviolet reflection, while those of females do not. Adults of both sexes have various colour forms.Most if not all species of this genus, as usual for Coliadinae, do not sequester toxins or other noxious compounds from their food plants. They are therefore a well-loved prey item of insectivores as compared to Pieris of the related Pierinae. They make up this disadvantage by being more nimble and better able to evade attacks by would-be predators.