Aphaenogaster boulderensis

This ant species often nests in vertical stone walls of desert canyons. Workers become active at dusk (crepuscular) and continue to forage into the night. Nests are difficult to find and to excavate.

Identification
The workers lack propodeal spines, although small angles may be present. The carinae on the clypeus are poorly developed, although a median carina is usually present. The head is elongated, and narrowed posteriorly. The eyes are relatively small, the maximum diameter is less than is the distance between the anterior border of the eye and insertion of the mandibles. The dorsum of the head is densely, but finely punctate, and partially smooth and shining. The mesosoma has similar sculpture, but most of the propodeum is relatively smooth and glossy.

This species could be confused with Aphaenogaster megommata. It differs in having a smaller eye, with about fifteen facets in the greatest diameter (20 facets in A. megommata), and in having the eye located about 1.5 times the greater greatest ocular diameter from the insertion of the mandible (side view of head). Additionally, it is ferrugineous red, as compared to the pale tan A. megommata.

Aphaenogaster boulderensis is one of the NA Aphaenogaster species without propodeal spines. The head and mesosoma are light brown, and the gaster is dark brown. The antennal scapes pass the occipital margin by one-third the length of the scape. (DeMarco, 2015)

Identification Keys including this Taxon
Key to US Aphaenogaster species

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

Nomenclature

 *  boulderensis. Aphaenogaster (Attomyrma) boulderensis Smith, M.R. 1941: 120 (w.) U.S.A.

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.

References based on Global Ant Biodiversity Informatics

 * Allred D. M. 1982. Ants of Utah. The Great Basin Naturalist 42: 415-511.
 * Allred, D.M. 1982. The ants of Utah. Great Basin Naturalist 42:415-511.
 * Boulton A.M. and P.S. Ward. 2002. Ants. Chapter 5 in A New island Biogeography of the Sea of Cortes. T.J. Case, M.L. Cody and E. Ezcurra. Oxford university Press.
 * Dattilo W. et al. 2019. MEXICO ANTS: incidence and abundance along the Nearctic-Neotropical interface. Ecology https://doi.org/10.1002/ecy.2944
 * Field Museum Collection, Chicago, Illinois (C. Moreau)
 * Gregg R. E. 1949. A new ant from southwestern United States (Hymenoptera, Formicidae). Proceedings of the Entomological Society of Washington 51: 171-174.
 * Johnson R. Personnal Database. Accessed on February 5th 2014 at http://www.asu.edu/clas/sirgtools/resources.htm
 * Johnson, R.A. and P.S. Ward. 2002. Biogeography and endemism of ants (Hymenoptera: Formicidae) in Baja California, Mexico: a first overview. Journal of Biogeography 29:10091026/
 * La Rivers I. 1968. A first listing of the ants of Nevada. Biological Society of Nevada, Occasional Papers 17: 1-12.
 * O'Keefe S. T., J. L. Cook, T. Dudek, D. F. Wunneburger, M. D. Guzman, R. N. Coulson, and S. B. Vinson. 2000. The Distribution of Texas Ants. The Southwestern Entomologist 22: 1-92.
 * Vasquez-Bolanos M. 2011. Checklist of the ants (Hymenoptera: Formicidae) from Mexico. Dugesiana 18(1): 95-133.
 * Vásquez-Bolaños M. 2011. Lista de especies de hormigas (Hymenoptera: Formicidae) para México. Dugesiana 18: 95-133
 * Ward P.S. and A.M. Boulton. 2002. Checklist of the ants of the Gulf of California Islands. In Island Biogeography of the sea of Cortes. T.J. Case, M.L. Cody and E. Ezcurra Editors. 690 pp.
 * Wheeler G. C., and J. Wheeler. 1986. The ants of Nevada. Los Angeles: Natural History Museum of Los Angeles County, vii + 138 pp.
 * Wheeler, G.C. and J. Wheeler. 1985. A checklist of Texas ants. Prairie Naturalist 17:49-64.