Furcula occidentalis (Lintner, 1878)
Western Furcula Moth
WA : Okanogan Co.
S. Fk. Twentymile Cr., 5810 ft
June 15, 1988, L. G. Crabo.
Specimen courtesy of LGCC
Photograph copyright: Merrill A. Peterson
Furcula occidentalis is our darkest Furcula and tends to be slightly larger than our other species (FW length 17–21 mm.). Both wings are a waxy light gray with a yellow tint, appearing nearly translucent like vellum paper. The forewings are heavily marked with dark hoary gray lines and black spots. The dark band across the median area is broad, with relatively straight margins in most individuals. The postmedial line consists of three separate strongly scalloped lines; the other lines consist of strong black dots on the veins. Patches of ochre are present near the transverse lines in some specimens. The hindwings are marked with a discal spot, faint diffuse marginal band, dark veins, and terminal spots on the veins. The anterior thorax is similar gray to the posterior thorax, occasionally lighter but not pure white. The male antenna is bipectinate while that of the female is simple.
This species can be identified by its curved forewing shape, translucent gray color, and pattern of dark bands and spots. It is most likely to be confused with the more common and widespread Furcula scolopendrina. It is differentiated from S. occidentalis by its pure white head and anterior thorax, white wings, and narrower and more irregular dark median area. Some F. occidentalis with strongly yellow tinted wings can resemble Furcula modesta, a rare northern species. It has less gray forewings and whiter hindwings than F. occidentalis, a yellow anterior thorax that is lighter than the posterior thorax, and its median dark band is usually hourglass-shaped with a median constriction.
The taxon occidentalis is considered to be a subspecies of the Holarctic species Furcula furcula (Clerk) in a recent check list of the New World prominents (Becker 2014)
This moth occurs in mixed forests, including boreal forest in British Columbia and a variety of forest types in western Washington.
Furcula occidentalis is found in forests of British Columbia, northern and western Washington, and northern Idaho. A single northwest Oregon locality is from Clatsop County.
The range of this species extends to the Atlantic. Forbes (1948) gives a range from Nova Scotia to New Jersey along the coast, and to Texas in the mid-continent. This moth appears to be absent form the Rocky Mountains south of the border between Alberta and British Columbia and does not occur on the West Coast south of the Columbia River mouth.
Willow (Salix spp.) in the Salicaceae is reported as the foodplant by Forbes (1948).
This species is single brooded and has been collected from late April through mid-August, with most records in late spring and early summer. The adults do not feed. It is nocturnal and comes to light.