This family contains about 1,200 species worldwide, with about 65 found in North America and 40 in Canada, although eight of these are non-resident migrants. It contains three subfamilies of which two have Canadian representatives. Most are of medium size, but there are both small and large tropical species, including some of our migrants. The adults of all species have six fully developed and functional legs, and the claws on the feet are strongly forked. Almost all are predominantly white, yellow, or orange in colour. The eggs, which are tall and vase-shaped, are usually laid singly on the foodplants. The larvae are cylindrical and covered with very short hair; they feed on dicotyledons and pupate in an upright position, attached by the cremaster at the bottom and a silken girdle around the middle.
This is the largest subfamily of pierids. Almost all feed on Brassicaceae (= Cruciferae) and three related families of plants; the Pine White (Neophasia menapia, which feeds on conifers, is one of the few exceptions. All the Canadian members of this subfamily have a white ground colour and some black markings, particularly on the upper surface. The undersides of some have a mixture of yellow and black scales that appear as green. The larvae are predominantly green and cylindrical in shape and covered with tiny hairs. Hibernation is usually in the pupal stage.
These butterflies are medium to fast flyers and regularly visit flowers. They usually fly earlier in the spring than most other butterflies, but some have several generations and are on the wing into late summer.
There are 18 members of this subfamily recorded in Canada, including one Asian species recently discovered in Yukon. One of the whites has been recorded only once as a stray in Ontario.
There are 22 species in this subfamily in Canada, with two occurring as far north as any butterfly in the world, on Ellesmere Island. All are yellow, green, or orange; in most the female patterns are distinctly different from the males and in many species some females occur in distinctive white forms.
The adults regularly visit flowers and sit with their wings tightly closed over their backs. Some members are avid mud-puddlers and will collect in the hundreds around muddy pools on dirt roads probing the dirt with their tongues.
As larvae, they feed mainly on Fabaceae (= Leguminosae), but some have adapted to other plant families such as the heath (Ericaceae) and willow (Salicaceae) families. The larvae are similar to those of the Pierinae, but unlike that subfamily, hibernate as larvae before pupation.
There are a number of southern sulphurs that only reach Canada as migrants. The resident Colias species are mostly non-migratory, although Colias eurytheme may be an exception.
In the genus Colias, there has been much speculation and controversy concerning defining and recognizing species. Over the years, many forms of the butterflies, especially species living in the Arctic and mountains, have been given different species names. Ferris (1993) attempts to bring some order to the confusion and his work has been mainly followed here, with some exceptions. He used ultraviolet reflectance patterns of the males' wings, geographic distribution, habitat, foodplant preference, and female wing patterns to define species.