Butterflies of Mexico, USA & Canada
Orange Sulphur
Colias eurytheme  BOISDUVAL, 1852
subfamily - COLIADINAE
Tribe -
Colias eurytheme male, Chiricahua mountains, Arizona, USA  Frank Model
There are over 80 species of Colias worldwide, of which the majority are inhabitants of temperate grasslands or sub-arctic tundra. In South America there are 5 species found on the Andean paramo and puna grasslands. There are 18 species in North America, two of which also occur in Central America; and there is one species endemic to Hawaii.
All Colias species are migratory in behaviour. Some simply move up and down mountainsides as the seasons advance, to take advantage of fresh growth of their larval foodplants and adult nectar sources. Others undertake much longer migrations - e.g. Colias crocea, which migrates annually from North Africa to northern Europe.
Colias are collectively known as Sulphurs in North America, but elsewhere in the world they are called Clouded Yellows. On the upper surface of the wings the ground colour varies from pure white to deep orange according to species, but the majority are some shade of yellow. Males of most species have narrow black wing borders. In females the borders are much wider, and the ground colour is always paler.
Colias eurytheme is found across most of the USA, and in Mexico.
Colias eurytheme male, Patagonia, Arizona, USA  Frank Model
Due to it's migratory behaviour, this species can be found in almost any habitat within it's range, but is most abundant in Medicago ( alfalfa ) fields.
The eggs are cream coloured when first laid, but soon turn crimson as the larva develops within. They are laid singly on the leaflets of Leguminosae - primarily on Medicago but also on Astragalus, Baptisia, Caragana, Cytisus, Hedysarum, Lathyrus, Lotus, Lupinus, Melilotus, Robinia, Thermopsis, Trifolium and Vicia. The fully grown caterpillar is green, with a faint mid-dorsal line and a prominent yellowish-white lateral line. The chrysalis is pale green, and is attached vertically and fixed by the cremaster and a silken girdle to a stem, usually but not always on the foodplant.
Adult behaviour
Males of all Colias species have a distinctive cycle of behaviour. They patrol back and forth over the breeding sites in search of females for several minutes at a time, and then suddenly swoop down and settle on bare soil. There they remain for several more minutes, even in hot sunny conditions when they would be expected to continue flying. After resting for a while they take flight again, but instead of patrolling for females they fly from flower to flower, nectaring for a few seconds before moving on to the next. This cycle is repeated throughout the morning until a receptive female is encountered. Copulation follows after a brief chase, and lasts for about an hour.
Females, after mating, follow a different cycle of behaviour. They typically spend several minutes nectaring, then rest for a while, and then go on an egg-laying run, during which they fly rapidly back and forth across the breeding site, stopping here and there for a moment to glue an egg to a leaf. They then have a rest and recovery period of about 15 minutes before repeating the cycle.
Colias eurytheme, male, Massachusetts, USA  Frank Model


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