Mustard White
Pieris napi
Description 1 1/2-1 5/8" (32-41 mm). Rounded wings. Above, delicate white. Below, cream-colored to yellowish; HW veins have light to heavy gray-olive or brown scaling; extreme forms also have scales along veins of other wing surfaces. Some summer broods lack dark vein-scaling. Sex spots (1 for male, 2 for female) occasionally appear on FW above, often blurred. If FW tips gray, vein-scaling is heavy.
Similar Species Cabbage White virtually always has gray FW tips and black sex spots on FW and lacks dark-dusted veins below. West Virginia White has smokier, diffused vein-scaling, rounder FW tips, and lacks yellowish tint to HW below. Pine White has black markings above and heavier dark markings below.
Life Cycle Pale, vase-shaped egg. Caterpillar forest-green with darker or yellowish back and side stripes.
Host plants include wide array of crucifers, such as cresses (Thlaspi, Arabis, and Barbarea) and toothworts (Dentaria).
Flight April-August in 2 or 3 broods.
Habitat Deciduous and coniferous woodlands, forest clearings and edges, roadsides, and in cool, moist places.
Range Cool, temperature portions of Northern Hemisphere. In North America, Alaska to Labrador south to Arizona, Montana, Lake States, and New York. Absent from S. California and entire Southeast.
Discussion Many lepidopterists have speculated about the Veined White's changed habitat following the introduction of the Cabbage White in 1860. The Cabbage White is reputed to have taken over as the common white of open landscapes, while the Veined White appears to have retreated to the woodlands, where it is better able to compete. But recent studies also suggest that these habitat changes may be the effect of human land use and not just interspecies competition. Both species have been found to coexist in many marginal places. The Veined White may well consist of more than one biological species, but until more distinctions are made it will be considered one variable, circumpolar species.
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