Myrmecocystus pyramicus

A primarily nocturnal foraging species that has nests that are topped by a low mounds.

Identification
A member of the pyramicus group of the Myrmecoystus subgenus Myrmecocystus .

Key to Myrmecocystus subgenus Myrmecocystus species.

This species has been adequately described by Smith (1951) and by Cole (1957). The strongly, angularly projecting propodeum is characteristic of this species and the closely related Myrmecocystus ewarti of California. The lack of erect hairs on the pronotum, disc of the first tergum and the extensor surface of the hind tibia will separate workers of pyramicus from those of ewarti. (Snelling 1976)

Distribution
United States. Southern Oregon and Idaho, south to Nevada and California.

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



Habitat
Collected in areas of Great Basin Sagebrush, Sagebrush Steppe and Saltbush-Greasewood Desert. In the Sagebrush Steppe of Idaho the elevational range is from 2350' to 5400'. In Nevada, where most records are from Great Basin Sagebrush areas, the elevation range is from about 4000' to 6700'. All records of this species are from Upper Sonoran or Transition Zone localities.

Biology
Snelling (1976) - A Great Basin species. Although foraging is mostly nocturnal, I have found Myrmecocystus pyramicus workers active outside the nest at midday in Oregon and Idaho. In both instances, though, rain was imminent and the sky was completely overcast. As expected, workers gather nectar from flowers and extrafloral nectaries, as well as from aphids and pseudococcids. They are also general scavengers. Repletes have been recovered from nests in Idaho.

The type series was collected by Ira La Rivers, with the notation "swarming nr. sundown." These specimens were collected on 7 April 1951. The reproductive have been taken in the nests in April, June and September. Mating flights evidently occur during spring and late summer rainy periods.

The type series was collected from a "... small, open mound nest in a sand clearing of Artemisia tridentate ..." Nests which I have observed were all marked by a low crateriform tumulus of fine to coarse sand grains. Since all these were seen during the summer rainy season, the tumuli were likely worn down. Most of the nests have been located in deep, sandy soil. An exception was that discovered in Owyhee County, Idaho. This nest was in deep alkali pan. This soil was very dense and excavation was not complete, but the nest probably continued down into an underlying layer of sand, as the tumulus consisted wholly of coarse sand particles.

Nomenclature

 *  pyramicus. Myrmecocystus pyramicus Smith, M.R. 1951c: 91, figs. 1-3 (w.) U.S.A. Cole, 1958b: 129 (q.m.). See also: Snelling, R.R. 1976: 132.

Worker
Snelling (1976) - Few or no erect hairs on malar area, antennal scape and tibiae (except beneath); propodeum, at juncture of dorsal and posterior faces, angularly produced upward; petiolar scale compressed; erect pronotal hairs, when present, shorter than apical breadth of scape. Female. Penultimate maxillary palpal segment narrowed basally and apically; tibiae without erect hairs; OOD 3 x OD; first tergum without erect discal hairs; rnesoscutum, between parapsides, with scattered coarse and fine punctures. Male. Forewing without fringe hairs on apical margin; scape and tibiae without erect hairs.

Measurements. HL 0.83-1.26; HW 0.73-1.23; SL 1.06-1.50; WL 1.2-1.9; PW 0.50-0.76.

Head: Longer than broad in all sizes, CI 85-97; distinctly shorter than scape, SI 117-132. In frontal view head broadest about midway between eyes and mandibular bases, sides thus convex but only slightly so; sides slightly narrowed toward mandibular insertions. Occiput, in frontal view, flattened, sides convex, not angulate. Eye large, 1.5-2.0 x first flagellomere; OMD 0.90-1.15 x EL. Mandible seven-toothed, occasionally with an intercalary denticle between subbasal and basal teeth.

Thorax: Slender, PW 0.38-0.46 x WL. Basal face of propodeum pyramidally produced upward at juncture with posterior face, about half as long as posterior face.

Petiole: Compressed when viewed in profile; from behind, crest narrow, angularly excised in middle; from above, about twice wider than long.

Vestiture: Erect cephalic hairs sparse, confined to clypeus, frontal lobes and occiput, those of clypeus much shorter on disc than at sides; longest occipital hairs less than 0.5 x MOD. Pronotal hairs sparse, sometimes absent, longest hairs always shorter than apical breadth of scape; mesonotum with 2-6 short erect hairs; propodeum without erect hairs. Petiolar scale with a few inconspicuous fine hairs on crest. First tergum with hairs on apical margin only; second tergum usually without erect discal hairs, occasionally a few fine hairs present laterad; following terga with scattered short discal hairs and usual longer marginal hairs. Scape, femora (except beneath) and tibiae (except beneath) without erect hairs (rarely 2 or 3 short suberect hairs on basal one-fourth of hind tibia).

Pubescence dilute, very short, but producing evident sheen on cephalic and thoracic dorsa and first three terga.

Integument: Front of head shiny, polished between punctures; clypeal punctures sparse, coarse; frontal punctures dense, fine; malar area shagreened, duller than frons, with scattered elongate fine punctures; integument otherwise moderately shiny, finely shagreened.

Color: Light brownish yellow, legs and antennae more yellowish; mandibular teeth ferruginous to blackish ferruginous.

Queen
Snelling (1976) - Measurements. HL 1.43-1.50 mm; HW 1.56-1.60; SL 1.46-1.53; EL 0.50-0.53; OMD 0.50-0.53; WL 3.3-3.4; PW 1.9-2.0.

Head: Broader than long, CI 107-109; a little shorter than to a little longer than, scape, SI 93-102. In frontal view, head broadest immediately above mandibular insertions, sides straight. In frontal view, occiput flat in middle, sides broadly rounded, without lateral angles. Eye large, about 1.5 x first flagellomere; EL 0.93-1.06 x OMD. OOD 3 x OD; IOD 3 x OD. Penultimate segment of maxillary palp broadest in middle, narrowed basally and apically.

Thorax: Robust, PW 0.55-0.60 x WL. In profile, posterior half of mesoscutum, scutellum and metanotum forming a continuous, flattened curve.

Petiole: In profile, compressed, crest sharp; distinctly angularly notched; from above, about twice wider than long.

Vestiture: Cephalic pilosity about as described for worker; pronotum with erect hairs on anterior margin; mesoscutum and scutellum with scattered long, erect yellowish hairs arising from coarse punctures; pleura with scattered erect long yellow hairs; propodeum without conspicuous erect hairs; first tergum with erect hairs on apical margin only; second tergum without erect discal hairs, or with a few scattered short hairs, third and fourth terga with scattered short erect hairs; scape without erect hairs except cluster near apex; femora with erect hairs on ventral margin only; hind tibia with sparse short subdecumbent hairs; very short fringe hairs present on apical margin of fore wing and apical and posterior margins of hind wing.

Pubescence long, yellowish, appressed to decumbent on head, thorax and appendages; fully appressed and abundant on first three terga, both shorter and sparser on fourth.

Integument: Clypeus coarsely punctate, interspaces shagreened and dull along midline, subpolished and shiny on lateral lobes; front of head otherwise shiny between punctures, frontal lobes finely and densely punctate, frons more finely and sparsely punctate, area between eyes and frontal lobes very sparsely and more coarsely punctate; occiput duller, very finely punctate and with finely shagreened interspaces; malar area dull, shagreened, coarsely punctate, punctures denser near mandible, those near eye elongate.

Pronotum moderately shiny between sparse, fine punctures, interspaces delicately shagreened. Parapsis densely, finely punctate, moderately shiny; disc of mesoscutum shinier, with sparse, very fine punctures laterad and scattered coarse punctures and broad central portion largely impunctate. Scutellum shiny, with sparse fine punctures, a little coarser and closer laterad. Pleura moderately shiny, closely and finely punctate. Propodeum slightly shiny, strongly shagreened, sparsely, finely and obscurely punctate.

First three terga moderately shiny, finely and sparsely punctate.

Color: Yellowish, cephalic, thoracic and gastric dorsa more brownish; legs and scapes paler. Fore wings transparent whitish, cells on costal margin with yellowish tint; veins and stigma ferruginous or brownish.

Male
Snelling (1976) - Measurements. HL 0.70-0.86; HW 0.66-0.76; SL 0.83-0.96; EL 0.33-0.40; WL 1.7-2.1; PW 0.95-1.13.

Head: Sides slightly convergent toward mandibular insertions; head a little longer than broad, CI 88-95; distinctly shorter than scape; OMD 0.50 x EL; anterior ocellus a little smaller than lateral ocelli; IOD 2.6-3.7 x OD; OOD 1.6-2.0 x OD. Mandible with preapical notch and/or preapical tooth.

Petiole: In profile, distinctly higher than long, sharply cuneate; in frontal view, sides somewhat convergent toward broadly emarginate crest; from above, about twice wider than long.

Vestiture: Erect hairs yellowish, sparse on head and thorax, longest on scutellum, but these distinctly shorter than MOD; propodeum without conspicuous erect hairs; scape and tibiae without erect hairs, or tibiae with scattered fine reclinate hairs; first two terga without erect hairs except on apical margins; remaining terga with numerous long yellowish hairs. Fore wing without fringe hairs; hind wing with fringe on posterior margin and scattered short hairs on apical margin.

Pubescence sparse and inconspicuous on head and thorax, denser on propodeum above and first two terga.

Integument: Moderately shiny, with piligerous micropunctures, a few scattered coarse punctures on scutum and pleura.

Color: Uniformly light brownish, appendages yellowish to yellowish brown. Wings whitish hyaline, stigma and veins pale yellowish.

Type Material
Snelling (1976) - Nevada Dominion Mine, Pyramid Mining District, 5 mi W Mullen Gap, Washoe Co., NEVADA, 7 April 1951 (I. La Rivers). Holotype and paratypes in USNM; additional paratypes in collections of, , and of Ira La Rivers.