The Margined White Butterfly is similar to the mustard white and replaces it in the West. The dark veins on the underside are grey-green and not dark green as in the Mustard White. They have a wingspan of up to 47 mm.
The summer form of this beautiful butterfly is pure white but in the spring you will see a black-tipped upper forewing. Males patrol for receptive females in the spring and after mating, the female will lay her eggs singly on the underside of plant leaves.
They have 2 flights, one in February and then another in September. You can find them in forests, meadows, deciduous woods, and around streams. They are common from southern British Columbia and Alberta to central California and southern New Mexico and all of Vancouver Island.