Oedemasia semirufescens (Walker, 1865)
Red-washed Prominent Moth
View Photographic Plate
WA : Okanogan Co.
Harts Pass Rd. @ Deadhorse Pt., 3841 ft
July 23, 1997, L. G. Crabo.
Specimen courtesy of LGCC
Photograph copyright: Merrill A. Peterson
Oedemasia semirufescens is a medium-sized, prominent moth (FW length 16–21 mm) with finely streaked pale blue-gray forewings with pale pinkish brown at the base and posterior margin. The forewings are relatively long, with scalloping of the outer margin that is most pronounced at the anal angle. In addition to the colors described above, the posterior wing base is dark brown. Specimens from west of the Cascades are more mottled than those from further east, and have a slight yellow cast to the entire wing. The transverse lines are obsolete or evident as fine lines on the veins. A thin black dash is present. The discal spot is a small black dot at the end of the cell, but can be absent. The male hindwing is pale grayish yellow with a dark gray anal angle. Females have darker hindwings with a light gray marginal band. The thorax is gray with darker posterior tufts. The male antenna is bipectinate, tapered toward the tip, while that of the female is simple.
Oedemasia pallida resembles Ianassa semirufescens but can be differentiated easily by its orange-brown color and black bar-shaped discal spot. Oedemasia salicis, another prominent moth, has similar wing color to O. semirufescens but has a stubbier forewing and more extensive dark brown and gray colors along its posterior area that extends to the outer wing margin.
This species is placed in the genus Oedemasia Packard in a recent check list of the New World prominents by Becker (2014), having previously been placed in the genus Oligocentria Herrich-Schaeffer.
This species is common in hardwood forests throughout North America. In the Pacific Northwest, it is particularly abundant in coastal rainforests and mixed hardwood forests west of the Cascades, but is also common in montane mixed hardwood-conifer forests of the Cascades and Rocky Mountain regions extending to the Blue Mountains.
Oedemasia semirufescens is found in forests throughout our region. It does not occur in xeric steppe habitats.
This species has a large range in North America. It occurs throughout the East, from Nova Scotia to Florida. Its range in the West is less well known, although it occurs in the Rocky Mountains.
This species is a generalist feeding on many kinds of hardwood trees and shrubs, particularly in the families Fagaceae, Betulaceae, Rosaceae, Aceraceae, and Salicaceae.
This species is probably single brooded and occurs from June through August in the Pacific Northwest. It is nocturnal and comes to light. Adults do not feed.