Colias is a genus of butterflies in the familyPieridae. They are usually 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.
Hybridization runs rampant in these polytypic and clinal butterflies, confounding molecular phylogenetics studies. In general, cladistic analyses of only one type of data (particularly mtDNA sequences) cannot be considered reliable. Regardless, the evolutionary distance within some "species" is so large that cryptic speciation rather than (or in addition to) interbreeding seems to be the cause. For example, the Beringian populations traditionally assigned to the northern clouded yellow (C. hecla) could warrant recognition as a species; hybridization between North American and Asian populations seems to have played a role in their evolution, but as a whole they appear to be a rather old and distinct lineage.
Species
Listed alphabetically:
Colias adelaidae Verhulst, 1991
Colias aegidii Verhulst, 1990
Colias alexandra W. H. Edwards, 1863 – Queen Alexandra's sulphur, Alexandra sulfur, or ultraviolet sulfur
Colias alpherakii Staudinger, 1882
Colias aquilonaris Grum-Grshimailo, 1899
Colias arida Alphéraky, 1889
Colias audre (Hemming, 1933)
Colias aurorina Herrich-Schäffer, 1850 – Greek clouded butterfly or dawn clouded yellow
Colias baeckeri Kotzsch, 1930
Colias balcanica Rebel, 1901
Colias behrii W. H. Edwards, 1866 – Behr's sulphur or Sierra green sulfur
Colias tyche (Böber, 1812) – pale Arctic clouded yellow, Arctic green sulphur, or Booth's sulphur
Colias viluiensis (Ménétriés, 1859)
Colias wanda Grum-Grshimaïlo, 1907
Colias wiskotti Staudinger, 1882
Distinguishing characteristics
Colias are usually some shade of yellow, orange or white. Their uppersides feature black borders (usually solid in males, often with pale spots in females). They always perch with wings closed, but upperside pattern may be seen faintly through the wing, or glimpsed in flight.
