Pheosia rimosa Packard, 1864
Black-rimmed Prominent Moth
WA : Okanogan Co.
Harts Pass Rd 2.1mi SE of Lost R to Deadhorse Point, 2480 ft
July 23, 1994, LG Crabo.
Specimen courtesy of LGCC
Photograph copyright: Merrill A. Peterson
Pheosia rimosa is a common large to very large prominent moth (FW length 21–26 mm in males; 25–33 in females) with light and dark geographic forms in the Pacific Northwest. The forewing is long with a rounded apex and appears slightly curved forward because the trailing margin of the hindwing is convex and the costa is slightly concave near the base. The margin is slightly scalloped and there is a small dark flange along the posterior margin. In the light form Pheosia rimosa rimosa the ground color of the anterior wing is white and the posterior wing and margin is tan. Black markings include a longitudinal mark from the wing base near the posterior margin that curves anteriorly along the outer margin, and a series of strong dashes on and near the distal costa that are strongest near the apex. The normal lines and spots are nearly obsolete. Usually only the anterior postmedial line is visible. The hindwing is white with dark gray marks on the slightly expanded anal angle. In the dark form Pheosia rimosa portlandia found west of the Cascade Crest most of the white portions of the forewing are dark gray, and the tan color of the nominate subspecies is replaced by darker brown. More extensive black marks are present between the veins, and the scalloped postmedial line is often visible as a pale line due to the darker color of the adjacent wing. The hindwing is similar to that of the nominate subspecies in pattern but is darker smoky gray rather than white . The thorax is gray with mild posterior tufting. The antennae are bipectinate, moderately wide in males and narrow in females.
Neither form of Pheosia rimosa is likely to be confused with other species in the Pacific Northwest. Both can be recognized by the long forewing shape with a flange along the posterior margin, black markings near the apex and curving along the posterior margin, and white hindwing with black at the anal angle.
The light and dark forms found east and west of the Cascades were considered to be separate species until 2010 when they were combined by Lafontaine and Schmidt. These authors consider the dark coastal form to be an ecophenotype, noting identical structure and mitochondrial DNA of the moths and the presence of intermediates in central British Columbia and Washington state. We prefer the use of subspecies given the fairly striking differences in the appearance of the two forms and the narrow region of intergradation. The western subspecies is Pheosia rimosa portlandia.
The taxonomy of North American Pheosia is being revised by Jim Miller. It is likely that what is currently considered to be a single transcontinental taxon will be split into eastern and western North American species. Both of these taxa might occur in the Northwest, with the eastern one entering northern British Columbia.
The larva is smooth, blue with an orange lateral stripe and a short caudal horn. It is illustrated by Powell & Opler (2009).
This species is common and widely distributed across much of North America in riparian habitats. In the Pacific Northwest, it is common in coastal rainforests and mixed hardwood forests at low to middle elevations west of the Cascades, particularly in riparian zones along creeks and rivers. East of the Cascades, it is common in mixed conifer-hardwood forests at middle to high elevations in the Rocky Mountain region, particularly in quaking aspen forests, but extends to riparian habitats in lowland desert regions at low elevations.
Pheosia rimosa rimosa is found in forests east of the Cascade crest. Pheosia rimosa portlandia is occurs in the western portions of our region. Specimens intermediate between the two can be found on both sides of the Cascade Range and are most common in interior British Columbia. This species is widespread in our region at least as far north as the Peace River region of northeastern British Columbia.
Populations currently assigned to this species are found across North America. Eastern populations are found from Labrador to North Carolina.
This species is a foodplant specialist feeding on Salicaceae, including both willows (Salix spp.) and cottonwoods or quaking aspen (Populus spp.).
The adults have a long flight season and have been found from mid April until late August. The bimodal phenogram with peaks in the spring and later summer suggests two broods in our area. Adults are nocturnal and come to light. As with other prominent moths the adults do not feed.
Lafontaine & Schmidt (2010)
Powell & Opler (2009)