Introduction
Butterflies in the subfamily Coliadinae, commonly known as Brimstones, Sulphurs, Grass Yellows and Clouded Yellows, are found in all parts of the world, and total about 300 species. The majority are migratory in behaviour – Colias crocea for example migrates each summer from north Africa to England, and Phoebis agarithe migrates seasonally from the Amazon lowlands to moderate altitudes in the Andes.
Colias euxanthe is one of several Clouded Yellow species which breed at high altitudes in the Andes, and is also migratory in behaviour, crossing seasonally from north to south along the Andean range, and also from the Pacific slope to the eastern Andes.
The butterfly occurs in Ecuador, Peru and Bolivia.
Habitats
This species breeds on dry puna grasslands and lightly grazed pastures at elevations between 2800-4000 metres, in areas bathed in the warm sunshine above the cloud line for most of the year.
Lifecycle
The lifecycle appears to be unrecorded, but the following characteristics are typical of the genus Colias, and are therefore probably applicable to euxanthe :
The eggs are bottle-shaped, ribbed vertically, in most species are creamy yellow or pale green when first laid, but later turn orange or dark crimson. They are nearly always laid singly, on the leaves of the larval foodplants.
The caterpillars are typically green, with a white or yellow lateral line that is sometimes edged with by a series or black or pinkish dashes. The spiracles are usually highlighted in yellow or orange.
The larval foodplants of Colias species are varied, North American Colias species for example feed on plants including Leguminous herbs such as Lotus, Vicia, Trifolium and Astragalus, and on dwarf sallows Salix, and bilberry Vaccinium. The pabula used by most neotropical species are unknown.
The chrysalis is usually green or straw coloured, and fixed vertically to a stem by the cremaster and a silken girdle.
Adult behaviour
Migrating adults fly rapidly across the Andean grasslands, stopping momentarily to nectar at any available flowers, and often patrolling back and forth along ridges.
At an altitude of about 3500m, on a plateau on the eastern Andes of southern Peru, I found what appeared to be a breeding site. At least 15 adults were flying in a small cultivated area of irrigated grassland. The crop was an unidentified grass, amongst which were growing various wild flowers. The butterflies periodically took to flight, always keeping low to the ground, flying rapidly from flower to flower, nectaring at gentians ( Gentianaceae ).
At another site, on steep Andean mountainsides in central Peru, I found a very isolated colony, with 6-8 adults on the wing, in a small field, lightly grazed by horses. Here, euxanthe shared it’s habitat with it’s larger and brighter relative Colias lesbia.
