Myrmecocystus creightoni

Occurs in sagebrush habitats, creating nests with a low crater.

Identification
A member of the subgenus Eremnocystus.

Key to Myrmecocystus subgenus Eremnocystus species.

This species appears to be most closely allied to Myrmecocystus yuma. Workers differ from those of that species in lacking erect hairs on the dorsum of the propodeum. In addition, workers of yuma possess six-eight erect hairs each on the pronotum and mesonotum; rarely a pair of very short, fine hairs may be present on the pronotum of Myrmecocystus creightoni, but the mesonotum seems always to lack erect hairs. Although Myrmecocystus lugubris workers also lack erect hairs on the pronotum and mesonotum, the petiolar scale is much more compressed than in Myrmecocystus creightoni.

The female of creightoni has the mesoscutum uniformly closely and finely punctate, without a defined median impunctate area. In this respect it agrees with the females of Myrmecocystus colei, but the mid and hind femora of colei have abundant erect hairs on all surfaces. The shape of the fourth and fifth segments of the maxillary palpus is as in yuma. The punctures of the upper half of the head are coarser and much sparser than in that species.

Males are poorly known in this subgenus. Those of Myrmecocystus hammettensis and colei lack fringe hairs on the apical margin of the forewing, present in creightoni. Males are not known for lugubris, Myrmecocystus perimeces, Myrmecocystus tenuinodis and yuma.

The larva has been described, as lugubris, by Wheeler and Wheeler (1968). The description was based on material from the type nest originally misidentified by me. (Snelling 1976)

Distribution
Only known from California.

This taxon was described from U.S.A.

Habitat
Low elevations in the mountain ranges along western fringes of Mojave and Colorado deserts.

Biology
Snelling (1976) - This species has been found in areas ranging from Juniper-sagebrush desert to coastal sagebrush. Elevation extends from about 850' to 4300'. Nest sites vary from compact clayey soil to coarse sand and are marked by a low crater. Those which are located on slopes and in heavy soil usually are not more than about three feet deep and repletes are present in the lower chambers. Nests situated in the deep sand of stream beds may exceed depths of four feet.

Foraging by this species is both matinal and crepuscular. Workers emerge shortly before sunrise and continue to be active until the surface temperature reaches about 75-80°F. In the afternoon, activity is resumed about 30-45 minutes prior to sunset, sometimes as much as 90 minutes before sunset if the soil surface is cool enough. Aphids on low vegetation are solicited for honeydew and nectar is gathered directly from plants. Large quantities of arthropod fragments are brought back to the nest.

Mating flights are known to take place in early spring after a light rain. The time of day at which the flight occurs is not known.

Nomenclature

 *  creightoni. Myrmecocystus creightoni Snelling, R.R. 1971a: 6, fig. 2 (w.q.m.) U.S.A. See also: Snelling, R.R. 1976: 98.

Worker
Snelling (1976) - Antennal scape with numerous fine, reclinate hairs, standing hairs absent or confined to apical one-sixth; dorsal face of propodeum without erect hairs; pronotum with two or no erect hairs. Female: Mesoscutum finely, uniformly densely punctate; wings without marginal fringe hairs. Male: Tibiae and scape without erect hairs; wings with marginal fringe hairs.

Measurements. HL 0.73-1.03 (0.90); HW 0.60-0.93 (0.80); SL 0.80-1.13 (1.00); WL 0.96-1.50 (1.30); PW 0.40-0.63 (0.56).

Head: Sides straight (slightly convex in largest workers), converging slightly toward mandibular insertion, longer than broad in all sizes, CI 78-93 (88); somewhat shorter than scape, SI 108-138 (125). Occiput broadly flattened in frontal view, with poorly indicated lateral corners. Eye small, about as long as first flagellomere; OMD 1.36-2.00 (1.45) X EL. Mandible with seven teeth on cutting margin, rarely with a minute intercalary denticle between basal and penultimate teeth.

Thorax: Slender to moderately robust, PW 0.36-0.50 x WL (0.41). In larger workers rear of mesonotum dropping sharply to metanotum. Basal face of propodeum as long as posterior face or slightly shorter, juncture of two faces distinctly rounded.

Petiole: Erect, in profile about twice higher than thick, not at all cuneate, summit rounded; crest flat in frontal view, not, or barely, impressed in middle; in dorsal view about twice as wide as thick.

Vestiture: Pubescence scattered on malar area, frons and occiput, nowhere concealing surface, longer than OD; longer and denser on thorax, especially on side of propodeum, longer and denser on gaster, but usually not concealing surface, sparse at sides of terga. Hairs on scape abundant, reclinate (rarely fully erect); occipital hairs shorter than maximum thickness of hind femur; thoracic dorsum usually lacking erect hairs, but three or four inconspicuous ones may be present toward sides; petiolar crest without conspicuous erect hairs; first tergum with erect discal hairs shorter than minimum thickness of hind femur; inner face of fore femur without erect hairs; outer face of middle and hind tibiae with few or no erect hairs.

Integument: Polished on clypeus, malar area and frons, duller on occiput, with scattered fine piligerous punctures on frons, clypeus and malar area, those on malar area often coarse and elongate. Thorax less shiny than head, densely shagreened, especially on sides of propodeum; gaster moderately shiny, densely and finely shagreened.

Color: Uniformly medium to dark brownish, legs lighter; mandibles and lateral clypeal lobes lighter, often yellowish.

Queen
Snelling (1976) - Measurements. HL 1.40; HW 1.43-1.46; SL 1.33; EL 0.40-0.43; OMD 0.50; WL 2.7-2.9; PW 1.8-1.9.

Head: In full face view with margins straight, converging slightly toward mandibular insertions, broad, CI 102-104; a little longer than scape, SI 90-93. Occiput, in frontal view, broad, flat, with rounded lateral angles. Eye small, barely longer than first flagellomere; OMD 1.15-1.25 X EL. IOD 3 x OD; OOD 3.5 X OD. Mandible with seven teeth.

Thorax: Robust, PW 0.65-0.66 X WL. In profile, posterior two-thirds of mesoscutum slightly convex, more flattened caudad, posterior margin below anterior margin of scutellum; scutellum, in profile, broadly convex; metanotum not protruding.

Petiole: In profile, compressed, about twice as high as thick at level of spiracle, crest thin; in frontal view, deeply notched; from above about 3.5 X wider than thick.

Vestiture: Cephalic pubescence yellowish, as long or longer than an ocellar diameter, much of it reclinate rather than appressed; scattered, not obscuring surface except on malar area above mandibular insertions. Thoracic and gastric pubescence white, appressed to reclinate; long, not concealing surface, but quite dense on gaster.

Scape hairs reclinate; malar area with a few long erect hairs in frontal view; thoracic dorsum with numerous erect yellowish hairs, longest on scutellum; erect hairs on disc of first tergum no longer than basal thickness of hind tibia; petiolar scale with a few short erect hairs on crest; fore femur without erect hairs on inner face; middle and hind tibiae with abundant suberect hairs on outer face. Wings without marginal fringe, but membrane with abundant short, erect hairs.

Integument: Head shiny, with coarse setigerous punctures on clypeus and upper half of malar area; frons and occiput with fine, well separated piligerous punctures; frontal lobes with dense, fine, punctures. Pronotum finely and densely punctate; mesopleura moderately shiny, densely shagreened, with fine punctures peripherally and scattered coarse, setigerous punctures; metapleura duller, densely shagreened, abundantly punctate, punctures finer than those in middle of mesopleura; mesoscutum densely, finely punctate, except for sparsely punctate area along midline, punctures of parapsis sparser than those of disc; mesoscutellar punctures equal to those of mesoscutum, sparser in middle; metanotum dull, closely shagreened and micropunctate; propodeum slightly shiny, roughened and closely shagreened. Gaster moderately shiny, with fine, dense piligerous punctures.

Color: Uniformly light brownish except for yellowish mandible, lateral clypeal lobes and lower half, or less, of gena. Wings hyaline, veins and stigma light brownish.

Male
Snelling (1976) - Measurements. HL 0.63-0.71; HW 0.60-0.63; SL 0.70-0.73; EL 0.23-0.25; OMD 0.13-0.15; WL 1.53-1.66; PW 0.93-1.00.

Head: In full face view, sides strongly convergent toward mandibular insertions, margins straight; head a little longer than broad, CI 90-94; distinctly shorter than scape, SI 114-115; OMD 0.56-0.60 x EL; ocelli subequal to one another; IOD 3.5-4.0 x OD; OOD 2.5-3.0 x OD. Mandibular margin simple, with preapical notch and two small denticulae basad, apical tooth as broad at base as long. Clypeus usually without preapical transverse depression.

Petiole: Scale in profile higher than long, evenly thick from base to near summit where it is narrowly rounded to slightly angulate; crest, seen from front, angulate at sides, broadly and rather deeply emarginate; in dorsal view, about 2.25 x wider than long.

Vestiture: White, appressed pubescence long, sparse on head and thoracic dorsum; more abundant on thoracic pleura, particularly on propodeum; longest on gaster, but nowhere concealing surface. Erect hairs sparse, short on head and thorax, yellowish. Middle of first tergum, in profile, with abundant very short, suberect whitish hairs; terga with scattered long to very long yellowish hairs, especially caudad and ventrally. Fore and hind wings fringed along apical and hind margins.

Integument: Head shiny, with scattered fine punctures. Mesoscutum shiny with sparse, fine punctures; propodeum, meso- and metapleura duller, densely shagreened, with scattered fine punctures; scutellum with a few very fine punctures. Gaster shiny, finely piligerously punctate.

Color: Uniformly light to very dark brownish, appendages and mandibles lighter. Wings hyaline, veins and stigma light brownish.

Type Material
Snelling (1976) - Holotype, allotype, and numerous paratypes of all castes, 2 mi S Pearblossom, 3500', Los Angeles Co., CALIF., 12 Feb. 1967 (R. R. Snelling). Holotype, allotype, most paratypes in ; paratypes in, GCW, , , REG,.

Etymology
It is my pleasure to dedicate this species to Professor W. S. Creighton for his outstanding contributions to the understanding of United States ants, with my thanks for his generosity and enthusiastic encouragement during this study.