Strumigenys arizonica

The type specimens were taken under a stone shared with a Trachymyrmex colony on a steep hillside in pinyon pine woodland (A. Mintzer, pers. comm.; as reported in Ward 1988). Subsequent collections have all been made from within the nests of the fungus-growing. The attine fungus garden requires a moist microenvironment. This likely attracts Collembola (springtails), which in turn are fed upon by Strumigenys arizonica.

Colonies typically consist of 1–2 dealate queens and 30–40 workers. Colonies produce males and alate queens from July through September, but interestingly they never produce both sexes in the same nest at the same time. Gray et al. (2018) provide a thorough account of distributions, the mutualism, and a link to a video showing this species capturing Collembola. (Booher, 2021)

Identification
Bolton (2000) - A member of the Strumigenys rostrata-group. Of the seven species in the group Strumigenys chiricahua and Strumigenys hyalina are immediately separated as they are the only ones to have a mandibular diastema that is decidedly longer than the basal tooth. Strumigenys californica is isolated by the presence of distinctly sculptured zones at the apices of the first gastral tergite and sternite, these zones remaining smooth and polished in all other species. In the relatively large rostrata (HL 0.61-0.72, HW 0.42-0.47) the dentition is coarse, with teeth 6 and 7 enlarged (see above), and its specialised projecting pilosity is characteristic: stout simple hairs are present in apicoscrobal position, at pronotal humerus and on mesonotum (one pair). The remaining three species, Strumigenys arizonica, Strumigenys bunki, Strumigenys carolinensis, average smaller (HL 0.54-0.64, HW 0.37-0.41) and have much smaller finer dentition (in particular teeth 6 and 7 are insignificant), nor do they have pilosity like rostrata at all the points mentioned; in particular all three lack an apicoscrobal hair. S. carolinensis has a pair of long flagellate hairs on the mesonotum, not developed in arizonica and bunki where mesonotal hairs are simple or absent. These last two species separate on relative development of spongiform tissue (see key) and on the complete lack of mesonotal standing hairs but presence of long fine gastral pilosity in bunki. Compared to this arizonica has a single pair of short simple erect hairs on the mesonotum and the first gastral tergite is sparsely clothed with very short stubbly simple hairs.

Flagellate hairs that project from the dorsal (outer) surface of the hind basitarsus are absent in rostrata and arizonica, always present in carolinensis. In bunki some specimens show such hairs, others do not. Because most bunki I have seen have been badly treated and poorly mounted I suspect that these fine and delicate hairs have been mostly stripped away and that they will always be present in fresh material.

Strumigenys mendezi is morphologically similar to S. arizonica, and sympatric with it, but nests freely, without associations with Trachymyrmex arizonensis or other ants (Booher, 2021).

Distribution
Strumigenys arizonica is most often collected above 1000 m in the Madrean Sky Islands of Arizona and Northern Mexico, in woodlands (oak, pine, juniper, mesquite) and riparian chaparral where its host Trachymyrmex arizonensis occurs (Booher, 2021).

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

Nomenclature

 *  arizonica. Smithistruma arizonica Ward, 1988: 121 (w.m.) U.S.A. Combination in Pyramica: Bolton, 1999: 1673; in Strumigenys: Baroni Urbani & De Andrade, 2007: 115. See also: Bolton, 2000: 125.

Worker
Bolton (2000) - TL 2.2, HL 0.58-0.64, HW 0.38-0.40, CI 60-67, ML 0.10-0.11, MI 15-19, SL 0.30-0.32, SI 79-83, PW 0.26-0.28, AL 0.59-0.64 (4 measured). Mandible with a minute diastema between basal lamella and basal tooth, diastema conspicuously shorter than length of basal tooth. Eye with 4-5 ommatidia in longest row. In profile maximum depth of ventral spongiform curtain of petiole less than the height of the peduncle. Spongiform appendages of postpetiole relatively small; lateral lobe in profile with its area less than that of the exposed smooth cuticle of the disc. In dorsal view postpetiole disc with sides only very thinly margined by spongiform tissue; maximum width across the spongiform tissue only ca 1.30 times the diameter of the disc. Base of first gastral sternite without distinct spongiform tissue, though a few short hairs may be present. Dorsolateral margin of head without an apicoscrobal hair. Cephalic dorsum behind level of clypeus without standing hairs of any form. Pronotal humeri each with a short fine flagellate hair. Dorsum of mesonotum with a single pair of very short simple erect hairs that are scarcely longer than the ground-pilosity. Standing hairs on first gastral tergite very short and fine, sparse and stubbly. Dorsal (outer) surfaces of middle and hind basitarsi without projecting flagellate hairs.

Type Material
Bolton (2000) - Holotype worker, paratype workers and male, U.S.A.: Arizona, Santa Cruz Co., Madera Canyon, ca 5600 ft, 2.viii.1975 (A. Mintzer) [examined].

References based on Global Ant Biodiversity Informatics

 * Cover S. P., and R. A. Johnson. 20011. Checklist of Arizona Ants. Downloaded on January 7th at http://www.asu.edu/clas/sirgtools/AZants-2011%20updatev2.pdf
 * Gray K. W., S. P. Cover, R. A. Johnson, and C. Rabeling. 2018. The dacetine ant Strumigenys arizonica, an apparent obligate commensal of the fungus-growing ant Trachymyrmex arizonensis in southwestern North America. Insectes Sociaux 65: 401–410.
 * Johnson R. Personnal Database. Accessed on February 5th 2014 at http://www.asu.edu/clas/sirgtools/resources.htm
 * Ward, P. S. 1988. Mesic Elemets in the Western Nearctic Ant Fauna: Taxonomic and Bilogical Notes on Amblyopone, Proceratium, and Smithistruma (Hymenoptera: Formicidae) Journal of the Kansas Entomological Society. 61:102-124