1 1/2-1 3/4" (38-44 mm). Creamy, off-white above with black network in upper FW tip and narrow, rectangular black spot across end of FW cell. Yellow veins and rich, yellow-green marbling across entire HW below in fairly separate bars and on FW tips below. Shiny blue-gray body hair.
Pearly Marblewing is smaller, whiter, with square spot off FW cell. Northern Marblewing is more densely marbled, other markings grayer. Olympia Marblewing has more open marbling on HW below and rosy flush above and below.
Long, jug-shaped egg. Caterpillar, to 3/4" (19 mm), dark green with bluish back stripe and yellow side lines as well as many tiny black projections. Chrysalis, to 3/4" (19 mm), purple at first, growing gray. Caterpillars feed on soft buds, flowers, and rarely, seed pods of host mustards, including several rock cress species (Arabis), mountain tansy mustard (Descurainia richardsonii), and other mustards.
February to mid-August, depending upon altitude and latitude; 2 broods in coastal California, 1 brood elsewhere.
Moister mountain areas, often among pine and aspen forests, trails, clearings, meadows, creek sides, and weedy lowlands in California.
Western mountains from Alaska and Alberta to central California and New Mexico; also in Great Lakes region to N. Michigan and Ontario.
A freshly emerged marblewing is a lovely but ephemeral sight since marblewings fly only briefly during springtime in any one locality. Marblewings appear later higher in the mountains, where spring comes in midsummer and all seasons except winter are compressed. Flying low, fast, and erratically, the Creamy Marblewing seldom pauses except to take nectar or to roost.