The upper side of the fore-wing of the western white butterfly has marginal markings that are lighter than the submarginal stripe. The fore-wing tip and hind wing have veins outlined with gray to green. the spring and fall forms have more prominent markings. The wing span is up to 6 cm.
The males patrol hilltops and ridges looking for receptive females. After mating, the females will lay eggs singly on host plants. Caterpillars will feed on leaves but prefer buds, flowers, and fruits. The caterpillars prefer the flowers and fruits of various members of the mustard family. The adults feed on flower nectar.
The Western White Butterfly hibernates through the winter. They have one flight in June in the far north and two flights in May and August on the southern coast.
On the outer islands, you will find them at high elevations and mountain peaks. The one pictured here was photographed up in the mountains above Cooper Creek. You will find them in Alaska south to central California and all the BC coast.