Strumigenys superstes

This species is a most unusual Strumigenys and is known from a single dealate queen collected in a pitfall trap between Flagstaff and the Grand Canyon, Arizona, United States, between late June and mid-July. Strumigenys superstes belongs to the excisa species-group, a morphologically distinct clade of shiny short-mandible species that once belonged in the genus Glamyromyrmex (Booher et al. 2021; Booher & Uhey 2020). Strumigenys superstes was collected in an undisturbed arid pinyon-juniper woodland on the Colorado Plateau. All other excisa species-group members have ranges in the Neotropics. (Booher, 2021)

Identification
Booher & Uhey (2020) - Strumigenys superstes is a member of the Strumigenys excisa-group and the only member of the group collected north of Mexico. In full-face view, the lateral outline of the head is interrupted by a pronounced indentation that forms a short right-corner triangular impression where the clypeus and frontal lobes fuse. Although Strumigenys azteca, Strumigenys rogata, Strumigenys erikae, and Strumigenys turpis might have shallow and evenly convex indentations, only Strumigenys asaphes has a similar sharp indentation. In S. asaphes the indentation is less pronounced and can be further differentiated from S. superstes by head pilosity (S. asaphes has scattered and numerous flagellate setae on the dorsum of head where S. superstes has only minute appressed simple setae). S. superstes most closely resembles S. azteca, but differs from all other azteca-complex (of the excisa-group) species in the following characters; the truncated apical free margin of the basal mandibular process is wider than the projected length from the apex to junction with the mandible; and absence of translucent flattened elongate specialized setae extending anteriorly from the apex of labral lobes (although one to two minute simple setae may project forward on each lobe). In all other azteca-complex species (Strumigenys prex, Strumigenys excisa, S. azteca, and S. rogata), the apical margin of the basal mandibular process is shorter than long and labral lobes have numerous elongate filiform and translucent elongate expanded setae that curve medially and project anterior past the apex of labral lobes.

S. superstes also differs from other azteca-complex queens in two key features: the mesoscutellum of S. superstes is free of sculpture, smooth and shining, and the greatest width of the mesonotum is shorter than the width between pronotal shoulders. All other azteca-complex species have queens with striate to rugulose sculptured mesoscutellums and have mesonotums 1.12-1.27 times wider than the distance between pronotal humeral angles.

Strumigenys excisa species-group species are morphologically distinctive, and immediately recognized among Nearctic natives, by their glossy-shining exoskeleton, enlarged conical teeth, and greatly expanded thin cuticular flanges on the postpetiole. The mandibles, labrum, and head capsule also are very modified, distinguishing them from most other Strumigenys, yet are similar to other short-mandible trap jaw species such as the Afrotropical tetragnatha, nitens, and loveridgei groups.

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

Biology
Strumigenys superstes is known only from a single queen collected from a pitfall trap at a mid-elevation (1940 m) pinyon-juniper woodland approximately 30 km south of the Grand Canyon. The smaller width of the mesosoma suggested the species might have reduced dispersibility by flight (Keller et al. 2014) and could potentially be a social parasite of another species.

Nomenclature

 * . Strumigenys superstes Booher & Uhey, 2020: 663, figs. 1-3 (q.) U.S.A.

Queen
Holotype HL = 0.542; HW = 0.483; ML = 0.091; PW = 0.343; SL = 0.232; FL = 0.371; HT = 0.360; EL = 0.102; WL = 0.643; CI = 89.1; MI = 16.9; SI = 48.2.

S. superstes agrees with the descriptions of the excisa group except for the minor difference in size of basal mandibular lamella mentioned previously. Mandibles with 10 teeth follow a widely truncated basal lamella without a diastemmic gap. The basal lamella has a complementary labral indentation where mandible can rest in locked position when open (a morphological feature of trap-jaw Strumigenys) (Gronenberg 1996). The basal lamella, although it projects past first teeth, is not as long as the following longest tooth when measured from base of tooth to apex. The labrum is heavily sclerotized at the base and slightly expanding along lateral free margins of labral lobes. Labral lobes truncated with flattened apices; with setae along apical and interior free margins of lobes with short simple appressed setae that do not project anteriorly past margins. Teeth stout and conical, gradually increase in size from tooth 1 through tooth 6 with basal three teeth obviously smaller than following three teeth; teeth 7 and 8 slightly smaller than their preceding tooth, tooth 9 similar sized as tooth 8, and apical tooth 10 enlarged. Teeth interlock along entire interior margin when closed.

Clypeus with anterolateral lobes that project past the medial clypeal anterior margin and is flatly transverse between lobes. Anteriolateral and lateral margins of clypeus rounded and convex, terminating in a sharp indentation where clypeus meets frontal lobes. Frontal lobes are expanded laterally and conceal preocular carinae in full-face view. Ventrolateral margin of head sharply marginate in front of eye, narrowly concave, and terminating in a minute inconspicuous tooth. Postbuccal impression in ventral view narrow and deep. Scape short, SI 48.2, without a prominent subbasal bend or projecting cuticle on anterior margin, expanded and swollen at mid-length, and only slightly dorso-ventrally flattened. Petiole 1.8 times wider than long. Post-petiole broadly U-shaped with a deep concave anterior border and convex posterior border; approximately four times wider (0.096) than long (0.393). First gastral tergite extremely elongate (1.4 times longer than wide).

Sculpture. Dorsum of head behind clypeus free of sculpture, sculpture on head limited to light reticulate striations along lateral borders of frontal lobes. Cuticle at side of head within scrobal area absent of sculpture; smooth and shining. Nodes of petiole and postpetiole free of sculpture and shining. Dorsum and side of pronotum and mesonotum free of sculpture and shining. Side of propodeum is free of sculpture and shining. Dorsal and declivitous faces of propodeum are lightly punctate with transverse striate sculpture. Basigastral costulae fine and numerous, extending about 2/3 the length of first gastral tergite; posterolaterad to conspicuous costulae the tergite superficially punctate.

Pilosity. No erect setae on the head. Erect to shallowly curved simple filiform setae limited to a pair at humeral angles, three pairs on mesonotal dorsum, two pairs on petiole, two pairs on postpetiole and on gaster. Dorsum of clypeus with short, fine, appressed pubescence and without any setae on lateral and anterior margins of clypeus. Pilosity on scape limited to inconspicuous appressed pubescence directed toward apex.

Spongiform Appendages. Ventral surfaces of petiole and post-petiole absent of cuticular spongiform process. Spongiform-like cuticle present only as lamellate petiolar and postpetiolar lateral lobes that are triangular and flat tooth-like process.

Type Material
Holotype. Known from a single alate queen. USA, Arizona, Coconino County, Blue Chute, 35.5868, -111.9694 ±100 m, 1942 m, 25 June-16 July 2014, pinyon-juniper woodland, pitfall trap under a Juniper tree, Collector Derek Uhey. (unique specimen identifier CASENT0749291).

Etymology
Meaning “survivor” and referring to the disjunct temperate locality of the species compared to the centralized Panamanian distribution of other members of the excisa group.