Aphaenogaster boulderensis

This ant species often nests in vertical stone walls. Workers become active at dusk (crepuscular) and continue to forage into the night.

Distribution based on Regional Taxon Lists
Nearctic Region: United States. Neotropical Region: Mexico.

Biology
This crepuscular and nocturnal ant often nests in vertical rock walls. Workers become active around dusk and continue to forage into the night.

Nomenclature

 *  boulderensis. Aphaenogaster (Attomyrma) boulderensis Smith, M.R. 1941: 120 (w.) U.S.A. Current subspecies: nominal plus smithi.

Description
Worker. - Length 4.5-5.5mm.

Head, excluding mandibles, one and three-tenths to one and four-tenths times as long as broad; sides appearing somewhat subparallel up to the posterior border of each eye, from which points they very gradually converge to form rounded posterior corners and a rounded occipital border; occipital border with a weakly developed flange. Mandible large, triangular, with approximately 8-10 teeth of variable size. Clypeus about twice as broad as long, with a rather distinct emargination in middle of anterior border. Frontal carinae subparallel throughout almost the posterior half of their length. Eye prominent, strongly convex, with approximately 15 facets in its greatest diameter; eye about one and one-half times its greatest diameter from base of mandible. Antennal scape slender, long, about one and one-forth times as long as head, not including mandibles. Dorsal surface of prothorax and anterior third of mesothorax, in profile, forming a regular but not strongly convex arch. Posterior two-thirds of mesonotum noticeably depressed, in profile forming a rather straight line. Mesoepinotal constriction distinct, broader than deep. Base of epinotum feebly convex, meeting the declivity at an obtuse angle; vestigial tubercles scarcely more evident than those of floridana. Petiolar node distinctly longer than pedicel; anterior surface in profile, meeting dorsal surface of pedicel in a very distinct obtuse angle; dorsal surface of petiole somewhat rounded, as is also the sloping posterior declivity, the two areas ill defined at the point where they merge into each other. Postpetiolar node scarcely longer than high, anterior surface forming a long slope, posterior surface more convex, declivous and short. From above, gaster subelliptical, broader than head.

Frontal area, posterior part of head, prothorax, anterior coxae, dorsal surface of petiole and postpetiole, and the gaster rather smooth and shining. Anterior two-thirds of head, including mandibles, the antennae, and tarsi, more opaque; mandibles somewhat coarsely and longitudinally striated. Clypeus and genae longitudinally rugulose, the former bearing a distinct median carina; frontal area with one or several longitudinal rugulae. Mesothorax, epinotum, and under surfaces of petiole and postpetiole with granulation-like shagreening; epinotum also finely and transversely rugulose. Coxae, femora, and gaster with exceedingly fine reticulae.

Hairs yellowish, moderately long but sparse, suberect to erect, on head, thorax, petiole, postpetiole, coxae, trochanters, gaster and also on ventral surfaces of femora. Antennae, tibiae, and tarsi with short, appressed hairs, these especially abundant and noticeable on the antennae. Light yellowish brown, often with darker mandibles, anterior portion of head, antennae, legs and gaster.

The type locality is Horseshoe Island in Lake Mead, of the Boulder Dam, Arizona. The ants were collected from under lava rocks at the top of the island.