Extracted from: TImberlake P. H., (1958). 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 III. University of California Press Berkeley and Los Angeles 1958, Volume 14, No. 5, pp. 303-410, plates 4-15.|
P. aemula is closely related to fraterna and may prove to be no more than a subspecies when sufficient material of both forms has been accumulated. It is distinguished from fraterna by the characters given in the key to the species.
Male.—Dark blue-green, with bright yellow markings. Mandibles except red tips, labrum, face below level of antennae, anterior end of cheeks, and postorbital line nearly to middle of eyes yellow. Lateral marks of face obliquely truncate above from outer margins of antennal socket to margin of eye just below level of foveae, with the green of frons intruding more or less between them and adjacent socket, or sometimes descending to upper end of subantennal plates; these plates sometimes narrowly black on inferior margin. Pronotum yellow, with a broad green band from flank to flank and the yellow on hind margin of disk interrupted, or the pronotum sometimes dark, with the collar, spot on anterior margin of each flank, an interrupted band on hind margin of disk, and the tubercles yellow. Thorax otherwise entirely dark except a yellow spot on meso- and metasternum between the middle and hind coxae. Abdomen yellow, with first tergite more or less entirely, basal band on tergite 2 and bands at junction of tergites 2-3 to 5-6 brownish fuscous or blackish; tergite 1 rarely with an interrupted, subapical yellow band, eometimes reduced to a small spot on each Bide, or often entirely absent. Legs yellow, with a streak on outerside of middle tibiae, the outer side of hind tibiae and basitarsi, and small joints of hind tarsi brown. Tegulae yellow at base and hyaline on outer margin. Wings almost clear hyaline, the nervures yellowish testaceous, the subcosta and margins of stigma brown.
Head rotund, about as broad as long. Mandibles tapering to acute apex and reaching to far margin of proboseidial cavity. Facial foveae faint and about twice as long as wide. Frons strongly tessellate, dull, and obscurely punctured. Mesonotum polished, with fine moderately sparse punctures. Pubescence whitish, that on mesonotum fine, thin, and erect. Subgenital plate slightly longer than wide and a little widened toward apex, which is broadly rounded. Aedeagus similar to that of fraterna, but basal orifice of caulis unusually narrow, and dorsal part of the parameral lobes covering much less of the lower part when viewed from above, and their marginal cilia somewhat longer and coarser. Length, 4.5-5 mm.; anterior wing, 3.3-3.5 mm.
Female.—Head and thorax dark yellowish green, with bright yellow markings. Mandibles except at tips, labrum, clypeus except usual pair of dots, lateral marks, and usually a supradypeal mark yellow. Lateral marks broad below, gradually narrowing above, then abruptly narrowed where they touch the foveae, with a short intrusion between foveae and eyes. Pronotum dark, with the collar and band on posterior margin of disk, usually narrowly confluent with a large mark on tubercles, yellow. Abdomen yellow, with five blackish bands; yellow band on tergite 1 usually moderately broad and entire, but varying from a very narrow and slightly interrupted condition to one much expanded mesad and enclosing a dark dot on each side. Legs yellow, the hind tibiae and tarsi, and outer margin of front and middle tibiae brownish fuscous. Scape of antennae and pedicel beneath clear yellow, the flagellum yellowish beneath and broadly fuscous above, as well as dorsal part of pedicel and a spot at apex of scape. Tegulae and wings as in male, except the nervures are paler and subcosta and margins of stigma slightly brownish.
Head unusually large and slightly broader than long. Mandibles massive, with the dilated inner margin abruptly narrowed close to apex. Facial foveae nearly uniform in width, about twice as wide as interval between tfhem and margin of eyes, and extending from level of middle of antennal sockets not much more than halfway to level of anterior ocellus. Pygidial plate moderately broad at base, the sides converging nearly straight to the rounded apex with the median notch small. Frons rather dull and tessellate, closely punctured between foveae and antennal sockets, and more sparsely punctured above to level of ocelli. Mesonotum polished and with moderately sparse fine punctures. Pubescence whitish, rather thin and erect on mesonotum and longer and denser as usual on cheeks and underparts of thorax. Length, 4.75-5.5 mm.; anterior wing, 3.5-3.9 mm.