Extracted from: Timberlake P.H., (1962). A Revisional Study of the Bees of the Genus Perdita F. Smith, with Special Reference to the Fauna of the Pacific Coast (Hymenoptera, Apoidea) Part V. University of California Publications in Entomology Editors, Volume 28, No. 1, pp. 1-124.|
P. semicrocea is a small, almost shining, black species with an orange-yellow abdomen. Some males have a very large head with broad but rounded and "unarmed cheeks and white face marks, in which it differs from allied species. The male genitalia (figs. 761, 762) are also very distinctive, particularly the peculiar sagittae. Cockerell has recorded this bee from the vicinity of Las Cruces and from "the White Sands near Whitewater" (evidently not Whitewater in Grant County), New Mexico, at flowers of Solidago, Gutierrezia, Aplopappus, and Aster. The type was collected on the campus of the New Mexico Agricultural College.
Female.—Head and thorax bluish green; clypeus, supraclypeal area, most of frons, disk of mesoscutum, and scutellum, black. Face entirely dark, but tubercles and collar of pronotum white, and sometimes a white streak on each side of posterior border of disk of pronotum. Abdomen orange yellow; tergite 1 usually fuscous; tergite 2 sometimes dark with a basal yellow band, or almost all yellow except for lateral margins and a dark spot on each side of apex; tergites 3 and 4 either unmarked or with a small fuscous spot on basal corners and a subapical spot on each side. Venter orange yellow without markings. Legs black; apex of femora, tibiae, and tarsi of front and middle legs, pale yellow. Antennae brown to fuscous, flagellum brownish yellow beneath. Mandibles white on basal half and red at apex. Proboscis and labrum dark. Tegulae hyaline, with base pale yellow. Wings whitish hyaline, nervures pallid, subcosta and margins of stigma pale yellowish.
Head broader than long; clypeus only moderately produced and strongly convex. Facial f oveae well impressed, short and broad, about four times as long as wide, very narrowly separated from eyes and placed slightly above level of antennal sockets. Mandibles reaching far margin of proboscidial fossa, tapering and with a small inner tooth. Proboscis rather short, apex of galeae in repose not reaching base of stipites. Pterostigma large but not quite equaling width of sub-marginal cells, part of marginal cell beneath it about as long as part beyond. Pygidial plate plane, with sides converging to narrow and slightly rounded apex. Head and thorax polished and shining; but vertex, anterior border of mesoscutum, and propodeum, more or less distinctly but very minutely tessellate. Frons and mesonotum almost impunctate; but face below antennae with sparse minute punctures, most distinct on clypeus. Face below antennae, vertex, and anterior border of mesonotum with sparse short white hairs; frons and disk of mesoscutum nude; cheeks and underparts of thorax with rather dense long hair. Length: about 3.45-4.5 mm.; anterior wing, 2.7-3 mm.
Male.—Head and thorax colored as in female, but with mandibles except red tips, labrum, and face below level of antennae, white. Lateral face marks ending truncately at level of antennae, but leaving outer margin of antennal sockets dark; margins of subantennal plates sometimes very narrowly dark. Tubercles, collar of pronotum, and an interrupted band on hind margin of disk, white. Abdomen colored as in female; legs much the same, but all trochanters, apex of hind femora, more or less of under margin of hind tibiae and hind tarsi, pale yellow. In one male (Petrified Forest, Arizona), legs mainly yellow, with dark parts of femora and hind tibiae reduced and pale brown. Scape of antennae yellowish white; a spot on apex of scape above, pedicel, and flagellum above, brown; flagellum brownish yellow beneath. Tegulae and wings as in female, except margins of stigma pale brownish.
Head rotund, barely wider than long, or in macrocephalous examples quadrate, with the cheeks very broad, but rounded and simple. Mandibles tapering to acute apex and reaching far margin of proboscidial fossa, but becoming slightly dilated on outer margin at base in macrocephalous specimens. Occiput shallowly and not broadly concave. Facial f oveae almost obsolete. Flanks of pronotum not impressed even in macrocephalous specimens. Sculpture and pubescence about as in female. Tergite 7 narrowed from base to rather narrow rounded apex. Subgenital plate about twice as long as wide, with nearly parallel sides and rounded apex; disk slightly ridged and with very short fine hair on apical part. Caulis of aedeagus quadrate, moderately longer than wide, about one and one-half times as broad as deep; dorsal lobes with blunt, slightly inturned points at apex; volsellae mainly concealed and subequal; parameral lobes slender and tapering; sagittae remarkably expanded on apical half both laterally and dorsoventrally, with apex divided into two divergent prongs by a very large, broad, and deep emargination, and expanded part as seen from side very high and rounded. Length: about 3-3.25 mm.; anterior wing, 2.3-2.7 mm.