Very similar to Eastern Pine Elfin, but Westerns Pine Elfins are not found in most of the Eastern United States, While Eastern Pine Elfins do not occur further west of the eastern Pine forests (western limits in Minnesota, Oklahoma, Texas). The two species do overlap ranges more broadly in Canada from northeastern British Columbia and northern Alberta eastward, but only the Western is found in the Rockies and westward.
In Western Pine Elfins the postmedian dark line crossing the middle of the front wing is usually straighter, without strong breaks and offsets (occasional individuals are not so); the discal cell of the front wing is crossed usually by only one bar at the end, and if there is a second it is usually very irregular and ill-defined; the dark submarginal chevrons on the under hind wing are usually nearly all sharply angled inward, often rather pointed; the row of dark markings just beyond the chevrons (toward the outer margin) generally tends to be in the form of rounded spots.
In Eastern Pine Elfins the postmedian dark line is usually strongly broken and offset; the discal cell usually has two distinct dark cross bars; and, the dark chevrons on the hind wing are usually less strongly bowed and more evenly rounded (though one near the anal angle is usually longer and more pointed); the row of dark markings just beyond the chevrons (toward the outer margin) generally tends to be in the form of a nearly continuous line.
Both species are variable, and occasional specimens may prove unidentifiable.
In United States - west from the western Great Plains and north of the southwestern deserts, mostly in mountains and broken terrain, and always where there are Pines. Also in northern part of Great Lakes states and in Maine.
In Canada widespread in association with Pines in the western mountains, and scattered across the rest of the country below the Arctic and north of the Praires.
one adult flight, mostly for about two or three weeks sometime from April to July (varies with local climate; earlier southward and at lower elevations)