Stenamma dyscheres

A rarely collected species that is poorly known. Specimens have been sifted from leaf litter in a mixed coniferous forest and from pine duff.

Identification
Worker with 2-4 facets in EL, OMD 2.0-4.0 x EL; median lobe of clypeus notched in frontal view; first tergite largely polished, basal one fourth or less with fine longitudinal striae; first sternite with sparse longitudinal striae which are coarse and conspicuous, or with numerous very fine striations, inters paces usually smooth and shiny, but fine punctulae may be present, particularly on sides.

Workers are medium ferruginous, legs and antennae yellowish, to brownish ferruginous with mandibles, lower third of head and appendages paler.

There are two forms of this species, which may in fact be two true species. More material is needed to resolve this issue. The type series consists of;similar workers in which the integument is moderately to strongly shiny on the thorax and petiolar nodes. The thoracic rugulae are coarse and well defined. The first gastric sternite has a number of widely spaced, rather coarse longitudinal striae and the corresponding tergite has numerous coarse striae basally, these about 0.2 mm long. The nodes of the petiole and postpetiole are conspicuously longitudinally rugulose.

Most of the remaining specimens are, on the average, smaller, with thoracic rugulae quite fine and the interspaces closely punctulate, hence only slightly shiny. The first gastric sternite is very finely and closely longitudinally striate with a few punctulae between striae, especially toward the sides. The base of the first tergite is closely and finely striate, the striae 0.13 mm long, or less. These closely punctulate specimens also usually have short, triangular propodeal spines, but the series from the Tehachapi Mountains has the spines about as long as in the types.

Among the species with sculptured gastric segments Stenamma dyscheres most closely resembles Stenamma punctatoventre and Stenamma californicum; Stenamma punctatoventre may be immediately separated by the shape of the median clypeal lobe, which is produced and appears truncate in frontal view. In Stenamma californicum the rugulae on the sides of the thorax are ·much reduced and very obscure because of the fine, dense punctulation; this is especially evident on the mesopleura which usually is without rugulae and on the propodeal sides which may have a few rugulae below the spiracle but none above it. In this species, too, the basal one-fourth or more of the first tergite is finely punctulate and without evident striations except the usual ones at the basal articulation. Finally, the sculpture of the first sternite consists of fine, dense punctulation. Those specimens of Stenamma dyscheres which possess dense punctulae on the sides of the thorax retain the coarse, conspicuous rugulae on the mesopleura and propodeal sides and the base of the first tergite is conspicuously striate, the articular striae interspersed with longer, finer supplementary striae. The sternite is striate, the striae coarse or fine and punctulae may be present laterally between striae.

Snelling 1973

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

Range
USA. California. Low to moderate elevations in the Sierra Nevada foothills south to Tejon Pass area of the Tehachapi Mountains; in the north, westward into the upper Sacramento Valley.

Nomenclature

 *  dyscheres. Stenamma dyscheres Snelling, R.R. 1973c: 21, figs. 28, 29, 34, 35 (w.q.m.) U.S.A.

Worker
Measurements. HL 0.68-0.90 (0.90); HW 0.52-0.75 (0.73); SL 0.47-0.63 (0.61); WL 0.77-1.03 (1.03); PW 0.37-0.50 (0.48).

Head. Distinctly longer than broad, CI 70-86 (81), sides nearly straight in frontal view, weakly to distinctly narrowed above. Eyes small, with 2-4 facets in EL, OMD 2.0-4.0 (2.6) x EL; OI 7-13 (9). Scape stout, shorter than HW, cylindrical at bend, distinctly thickened near apex, SI 78-97 (84). Mandibles moderately shiny, coarsely striate over entire length, more finely so in small specimens; cutting margin with six or seven teeth, apical and preapical teeth large, sub-basal teeth often reduced, basal tooth distinct, triangular. Clypeus shiny, median lobe longitudinally depressed and laterally carinulate, weakly to strongly notched in frontal view, with or without transverse carinula below summit of declivity; in profile, lobe not exceeding clypeal margin, declivity straight to distinctly concave in lower half or less. Frontal lobe barely shiny, with one or two longitudinal rugulae; front and sides of head with fine, widely spaced longitudinal rugulae, weaker and forming reticulae above, especially at sides, interspaces slightly shiny, finely punctulate and with scattered coarse, piligerous punctures.

Thorax. Pronotal neck closely punctulate and slightly shiny, declivity shiny, with one to four fine irregular transverse rugulae, interspaces lightly punctulate; sides with widely spaced longitudinal rugae, inters paces smooth, shiny, with a few fine punctulae; or interspaces slightly shiny and densely punctulate. Promesonotum with irregular longitudinal rugae for most of length (a few transverse rugulae anteriorly), interspaces smooth, shiny, with scattered fine punctulae; or closely and finely longitudinally rugulose, interspaces slightly shiny, closely and finely punctulate. Mesopleura coarsely rugulose or reticulate, moderately shiny, inters paces lightly and sparsely punctulate; or dull, densely punctulate and rugulose; or densely punctulate and without rugulae. Sides of pronotum with coarse longitudinal rugulae, slightly to moderately shiny, interspaces lightly, but usually closely, punctulate; or rugulae largely obsolescent, surface barely shiny, sharply and closely punctulate; basal area moderately shiny, finely and sparsely punctulate, with a few obscure transverse rugulae; or slightly shiny, densely and finely punctulate, with few or no transverse rugulae; spines acute, about as long as distance between them; or short, triangular and separated by about twice their length. Metanotal groove shallow, usually broad in profile.

Petiole. Dorsal face of anterior peduncle about as long as front of node; node, in profile, broadly cuneate with rounded crest; ventrally with or without anterior tooth or projection. Postpetiole evenly convex in profile; from above, slightly wider than long, distinctly broader caudad; nodes with distinct to obscure longitudinal rugulae, surface shiny and sparsely punctulate to slightly shiny and densely punctulate; remainder closely punctulate.

Gaster. First tergite with conspicuous fine striae on basal one-fourth or less, striae sometimes reduced to extreme basal one-sixth, but then exceptionally fine and dense; segment otherwise smooth and shiny, with scattered fine piligerous punctures. First sternite with a variable number of sharply defined, widely spaced striae on basal one-third or more, inters paces smooth and shiny; or basal one-third or more with numerous fine striae, inters paces sometimes weakly punctulate, especially laterad; rarely, striae are restricted to basal onefifth and along extreme sides, most of segment smooth and shiny.

Pilosity. Front of head with intermixed sparse long and short hairs; thoracic dorsum with scattered long, erect hairs of variable length; remainder of body with sparse suberect hairs.

Color. Medium ferruginous, legs and antennae yellowish, to brownish ferruginous with mandibles, lower third of head and appendages paler.

Queen
Measurements. HL 0.83-0.93; HW 0.70-0.78; SL 0.60-0.66; WL 1.20-1.30; PW 0.60-0.66.

Head. Longer than broad, CI 81-85, sides mostly parallel, but slightly convergent above in frontal view. Eyes convex, of moderate size, OMD 0.77- 0.92 x EL; OI 21-24. Scape stout, cylindrical at base and somewhat thickened toward apex, SI 81-87. Mandibles moderately shiny, rugose over entire length, with 6 or 7 teeth on cutting margin, apical and two preapical teeth large, subbasal teeth much reduced, basal tooth usually distinct. Clypeus as described for worker. Sculpture as described for worker but rugulae a little coarser and reticulae more numerous.

Thorax. Pronotal neck slightly shiny, densely and finely punctulate; declivity moderately shiny, with irregular fine transverse rugulae, interspaces lightly punctulate; sides with several coarse, widely spaced rugae, interspaces shiny, lightly to moderately shiny. Pleurae moderately to strongly shiny, with coarse longitudinal rugae above, but mostly smooth, interrugal spaces shiny, sometimes with light punctulation. Mesocutum and scutellum longitudinally coarsely rugulose, interspaces moderately shiny and lightly to moderately punctulate. Propodeal sides longitudinally rugose, inters paces narrow, lightly to moderately shiny; basal area slightly shiny, closely punctulate; declivitous area smooth and shiny; spines as described for worker.

Petiole. As described for worker.

Gaster. As described for worker.

Pilosity. About as in worker, but longer and a little more abundant.

Color. As described for worker.

Type Material
Holotype worker, allotype male and 9 workers, 21 male paratypes: Bull Flat, 3600', T5N, R.18E, Tuolumne Co., CALIF., 6 Sept. 1967 (G. C. and J. N. Wheeler; #187, CALIF). Holotype, allotype and 2 workers, 7 male paratypes in ; 2 workers, 4 male paratypes in GCW; 1 worker, 2 male para types in each:, , , ACC, WSC.

Etymology
Descriptive. Dyscheres, Gr., vexatious or difficult; in allusion to the extreme variability of this species and the difficulty in characterizing it.

Additional References

 * Snelling, R. R. 1973. Studies on California ants. 7. The genus Stenamma (Hymenoptera: Formicidae). Contributions in Science (Los Angeles). 245:1-38.