General Description

A relatively non-descript grey-brown geometrid, although the three to four evenly spaced dark brown crescents along the forewing will usually distinguish it as an Itame. Darker PM line usually present on both fore and hindwing, often broad at the forewing anal margin to form a band extending at most halfway up wing. The fringe varies from dark brown to beige. The females have reduced forewings and rarely fly (Doak, 2000). Closely related to I. occiduaria (with which it was once considered to be conspecific), but the ground color is mousy brown not yellowish. Specimens of occiduaria from the foothills west of Calgary are brownish yellow somewhat approaching andersoni, but are slightly smaller with a more uniform color and not finely speckled with brown. The larvae also differ in color pattern (McGuffin 1956). Ferguson (1953) in revising this species group, failed to find consistent genitalic differences between occiduaria and andersoni.