The Clouded Sulphur belongs to the family Pieridae, a large worldwide family of butterflies which includes all of the whites, sulphurs, marbles and orangetips. Butterflies in this family bear a full complement of six functional legs and are typically medium-sized species which spend a great deal of time on the wing. Although some species are common or abundant, they are typically flighty and difficult to approach. Pierids typically have white or yellow wings, and can be very similar in appearance worldwide, thus are often rather difficult to identify. In Washington there are 17 species of pierids, including 7 sulphurs, 7 whites, 2 marbles and 1 orangetip. Most sulphurs, particularly males, have all yellow wings, very bright yellow in some species; females usually have yellow wings as well, although in some species a portion of the population will be white. Sulphurs are fond of mudding and sometimes males can be found in large aggregations around wet muddy spots.

The Clouded Sulphur is a widespread species occurring across North America. In Washington the species occurs throughout the eastern part of the state east  of  the  Cascade Mountains, and also in spotty distribution on the west side. Colias philodice may be found in lowland agricultural fields, particularly where alfalfa is grown, or well into the mountains, particularly in clearings and along roadways.

The Clouded Sulphur is multiple-brooded in Washington and has a very long reported flight period extending from mid April to early November. All of our sulphurs overwinter as partially grown larvae, a feature which distinctly separates them from the other pierids which overwinter in the chrysalis (or egg in one species). C. philodice larvae break diapause and begin feeding in the spring as soon as their foodplant begins growing. Foodplants include a variety of legumes, particularly various locoweeds (Astragalus) but also wild pea (Lathyrus), clover (Trifolium), sweet clover (Melilotus), vetch (Vicia), alfalfa (Medicago), lupine (Lupinus) and others. Adult females captured near Vantage in the early spring, and caged with both alfalfa and the locally-occurring Astragalus, oviposited initially only on the Astragalus, but then also abundantly on the alfalfa as the Astragalus began to wilt. The larvae were reared on alfalfa, and they grew and matured quickly. The slender green larvae feed on the leaves of the host plants, then usually wander to a hidden area to pupate. On emerging to the adult stage the cycle is repeated, and this continues apparently as long as succulent foodplants remain available. There is some upslope migration into the mountains as the season progresses.

The sexes are dimorphic, as in most of our sulphurs, and are best separated by their black dorsal forewing borders; males have a solid black border while females have a broader but broken, “mottled” border. The Clouded Sulphur can be separated from all other Washington sulphurs except the Orange Sulphur by the presence of a row of brown “eurytheme spots” paralleling the outer margin of the ventral hindwing. Males of C. philodice can be separated from Orange Sulphur, C. eurytheme males by wing color, the C. philodice being entirely yellow and C. eurytheme having distinct orange patches dorsally.

Additionally C. eurytheme males reflect ultraviolet light, but this is not visible to the human eye in the field. C. philodice and C. eurytheme sometimes interbreed where they occur together, and females of the two species cannot be reliably distinguished. The two species have been heavily studied (partly because C. eurytheme is regarded as an agricultural pest) and are considered distinct as the offspring of hybrids always revert to one of the two parental types rather than some intermediate form.

All Photos by Dave Nunnallee

G’num 2005Vol6No4