Didea species are large with broad flat abdomen bearing strongly emarginate or narrowly divided yellow, yellow-green, or pale green bands; eyes with moderately long but extremely sparse pili; and metasternum pilose. Didea fuscipes has the basal half of cell BM microtrichose only on posterior one-third, and tergum 4th with yellow fascia deeply emarginate but entire.
Adapted from Vockeroth (1992).
Head: Frons yellow, usually with small dark macula above base of each antenna. Face yellow, including most of lower margin, with narrow brown medial vitta on lower half indistinct in some specimens. Holoptic, eyes with moderately long but extremely sparse pili. Scape rather large, twice as long as broad.
Thorax: scutum black, shining or subshining. Scutellum dull yellow with only lateral corners darkened, usually with black pili only on posterior half or less, rarely with some black pili on anterior half; ventral scutellar fringe short and sparse. Pleura black with densely pale-pruinose areas on upper half. Anterior anepisternum bare; dorsal and ventral katepisternal pile patches broadly separated; meron bare; metaepisternum with some pili; metasternum pilose. Wing membrane with bare areas at base of cell r, in basal two-thirds of cell br, in most of anterior two-thirds of cell bm, and in narrow strip behind CuP. Vein R4+5 broadly and rather deeply dipped into cell r4+5. Lower calypter usually with very few fine pale erect scattered hairs on upper surface. Metacoxa with several pili at posteromedial apical angle.
Abdomen: strongly margined. Markings of terga yellow to yellow-green; bands of terga 3rd and 4th
strongly narrowed medially but undivided; tergum 5th at least slightly yellowish to reddish anterolaterally.
Arms of dark Y-shaped macula above antennae narrower than anteromedian yellow area. Tergum 5th yellow with black posteromedian triangle.
GenBank accession number for this species are: protein-coding COI gene (EF127301) and rRNA 28S gene (EF127380).
Species similar to Didea alneti, but the lattest differs by having entirely black pilose or with yellow pile on extreme anterior margin; basal half of cell bm microtrichose on posterior two-thirds or more; tergum 4th with yellow fascia narrowly divided; tergum 5th black in male, black or with pair of small yellow maculae in female (from Vockeroth 1992).
Didea fuscipes was included in the molecular analysis of Mengual et al. (2008) and was resolved as sister taxon of Didea intermedia, recovering the genus as monophyletic. Didea wa resolved as sister group of the genus Megasyrphus; in congruence with larval characters (Rotheray and Gilbert 1989).
Larvae of Didea fuscipes have been reported feeding on several species of aphids (Aphididae) (Rojo et al. 2003).
Nearctic species known from British Columbia to Nova Scotia, south to Oregon, New Mexico, Mississippi and North Carolina.