Synonyms and other taxonomic changes
Polia nimbosa (Guenée, 1852)
Eurios nimbosa (Guenée, 1852)
Aplecta nimbosa Guenée, 1852
Phylogenetic sequence # 932867
Explanation of Names
NIMBOSA: from the Latin "nimbus" (rain cloud; storm cloud); probably refers to the dark mottling on the forewing, reminiscent of the color of a storm cloud, and the origin of the common name Stormy Arches
Numbers
Lafontaine & Schmidt (2010) listed nine species of the genus
Polia in America north of Mexico.
(1)Size
Wingspan 40-65 mm.
Forewing length length 23-27 mm.
(2)Identification
Adult: tegulae ("shoulder pads" on thorax) pale with black margins; forewing pale gray, mottled with gray and black; orbicular, claviform, and reniform spots with sharp black outlines; reniform spot strongly curved; AM and PM lines double, scalloped; PM line resembles a sinuous series of connected white chevrons; ST line jagged, and has two small black spots near anal angle (the spots are either side-by-side or joined, and are a distinctive feature).
hindwing grayish or brownish; median line, originating near anal angle, bordered distally by pale band, followed by dark band along outer margin.
Crumb (1956) has description of the larvae.
(3)
Genitalia:
Larva: very similar to Lachinipolia lorea 10405. Polia nimbosa has a faint spiracular line but Lachinipolia doesn't. There seems to be a ridge across the back of A8 on Polia but not on Lachinipolia. The spiracles on Polia are supposed to be tan with a black rim. The head of Polia has a light center with dark lines down the face.
Range
coast to coast in northern United States and southern Canada (Newfoundland to North Carolina, west to northern California
(4), north to British Columbia)
Season
The flight period appears to be May to September with the peak in July.
(5)Food
larvae feed on leaves of alder, birch, gooseberry (Ribes spp.), huckleberry (Gaylussacia spp.), maple, willow
See Also
Cloudy Arches (Polia imbrifera) forewing has a less distinct PM line, a more noticeable whitish ST line, and a relatively large
triangular dark patch near anal angle (rather than two small black dots set side-by-side, as in
P. nimbosa)
Polia propodea has dark "shoulder pads" (tegulae), a darker gray forewing with a distinct blackish ST line, and two tiny white spots in lower corner of reniform spot - lacking in
P. nimbosa Print References
Guenée, 1852. Noctuidae II. pp. 77, 769.
Powell, J.A. & P.A. Opler 2009.
Moths of Western North America. University of California Press. plate 55, fig. 25; p. 303.
(6)Internet References
pinned adult image by John Glaser, plus food plants (Larry Line, Maryland)
pinned adult images of male and female (James Adams, Dalton State College, Georgia)
distribution in Canada list of provinces (U. of Alberta, using CBIF data)
