Myrmecocystus tenuinodis

Identification
A member of the subgenus Eremnocystus.

Key to Myrmecocystus subgenus Eremnocystus species.

Worker - Petiole strongly compressed; fully erect hairs present on propodeal dorsum, often present on scape; femora, including inner face of fore and dorsal face of hind femora, and tibiae with abundant erect hairs. Female: Mesoscutum shiny, median area with scattered punctures, parapsis with denser, but still sparse punctures; fore femur with reclinate or erect hairs on all surfaces; fore and hind wings with erect membrane hairs; forewing without fringe hairs; hind wing with fringe hairs on posterior margin.

Although the petiolar scale is almost as thin, in profile, as it is in Myrmecocystus lugubris, this species has a number of conspicuous erect hairs on the dorsum of the propodeum. There are also numerous erect hairs on the extensor surfaces of the hind femur and tibia. The hind femur of lugubris has no erect hairs on the extensor surface and few or none on that surface of the tibia. The petiolar scale is thinner than is that of yuma from which tenuinodis also differs in the more pilose legs.

In the female the mesoscutum is impunctate in the middle, by which it may immediately be separated from those of Myrmecocystus creightoni and Myrmecocystus colei. The distinctly clavate fourth segment of the maxillary palp will separate the female from that of all species except Myrmecocystus hammettensis, but in that species the upper half of the mesopleura is polished between scattered coarse, somewhat elongate punctures and the scutellum has extensive areas of very sparse punctation. The summit of the first tergum, in the middle, and the disc of the second are moderately shiny and uniformly, closely micropunctate in  Myrmecocystus tenuinodis, but polished and very sparsely punctate in hammettensis. (Snelling 1976)

Distribution
United States, Mexico. Mojave and Colorado Deserts, from southern Nevada to northern Sonora; probably also in northern Baja California.

This taxon was described from U.S.A.

Biology
The habitats of this ant are all in areas of Creosote bush or Creosote bush-Bur sage Desert, at elevations up to at least 4000 feet. The nests are surmounted by low craters up to 20 cm in diameter and are located in areas of fine sand.

Foraging is both matinal and crepuscular. The foragers have been taken at nectaries of Coldenia sp. (Boraginaceae) near Yuma and on Malacothrix sp. (Asteraceaes at the type locality. They seem to limit their activities to low vegetation, none having been taken more than one meter above ground level. At Yuma, also, workers were seen carrying immature cicadellids (mostly first or second instar) back to the nest. Arthropod fragments are commonly found in the debris around the nest. Repletes have been taken from nests at the type locality.

Creighton took females of this species in flight on 16 Feb. 1963, after a recent rain which soaked the surface to a depth of about six inches. His notes do not indicate time of day of the flights.

Near Thousand Palms I found foraging files of this ant. On both occasions, the files were irregular, with ants well-spaced, and often running parallel with, but about a centimeter to either side of the path. Surface activity by this ant is largely during the spring and autumnal months. There apparently is little or no foraging done between the middle of May and the middle of October. Marked nests located near Thousand Palms which were visited during this period were always closed and the tumuli in disrepair. Summer-long aestivation may be normal for this and other hot desert species.

Castes
Male unknown.

Nomenclature

 *  tenuinodis. Myrmecocystus (Eremnocystus) tenuinodis Snelling, R.R. 1976: 107, figs. 241-247 (w.q.) U.S.A.

Worker
Measurements. HL 0.70-1.03 (0.83); HW 0.63-1.00 (0.76); SL 0.73-1.03 (0.86); WL 0.86-1.43 (1.03); PW 0.40-0.63 (0.50).

Head: In all sizes varying from distinctly to slightly broader than long, CI 82-96 (92), slightly shorter than, or as long as scape, SI 100-113 (104); in frontal view sides straight or feebly convex in largest workers; occiput, in frontal view, barely convex, sides broadly rounded. Eye small, barely longer than first flagellomere; OMD 1.39-1.68 (1.43) x EL. Mandible septendentate.

Thorax: Moderately robust, PW 0.42-0.50 (0.48) x WL. Mesonotum, in profile, gently convex, not abruptly sloping behind. Propodeum higher than long, basal face broadly rounded into posterior face, latter about twice as long as former.

Petiole: Scale erect, about thrice higher than thick; crest sharp; crest, in frontal view, narrowed above, weakly angularly emarginate; from above, more than twice wider than thick.

Vestiture: Cephalic pubescence short, sparse on occiput, scattered elsewhere; thoracic pubescence generally sparse, a little denser on pleura and propodeum. First two terga with pubescence sufficiently dense to form sheen; third and following segments with scattered pubescence, occasionally none at all.

Malar area usually with a few (up to six) erect hairs visible in frontal view; clypeus, frontal lobes and occiput with fine, acuminate erect hairs, longest occipital hairs about equal to 0.5 x MOD. Pronotum and mesonotum with numerous standing hairs; metanotum without erect hairs; basal face of propodeum with a cluster of fine, erect hairs at juncture with posterior face. Petiolar crest with a few short, fine, erect hairs. First two terga with sparse erect hairs. Scape usually with abundant fine reclinate hairs, rarely with scattered fully erect hairs; inner face of fore femur and dorsal face of hind femur with erect hairs; hind tibia usually with abundant erect hairs on outer face, but may be reduced or lacking in small individuals.

Integument: Clypeus polished and shiny; frontal lobes shiny to moderately shiny, lightly shagreened, with scattered fine, obscure punctures; frons moderately shiny, lightly shagreened; occiput duller, more densely shagreened; malar area moderately shiny, more closely shagreened near eyes and mandibular insertions, with scattered fine punctures. Thorax slightly shiny, closely shagreened, more strongly so on propodeum. First tergum slightly shiny, densely shagreened; second segment shinier and more lightly shagreened; remaining segments shinier and more weakly shagreened than second.

Color: Light to dark brownish, gaster sometimes slightly darker than head and thorax; appendages paler; mandibles, sides of clypeus and malar area near mandibular bases, yellowish.

Queen
Measurements. HL 1.36-1.40; HW 1.43-1.46; SL 1.26-1.30; EL 0.40; OMD 0.50; WL 2.9-3.0; PW 1.8-1.9.

Head: Slightly broader than long, CI 104; malar margins, in frontal view, straight, slightly narrowed toward mandibular bases; occiput flat in frontal view, sides slightly angulate, broadly rounded; a little longer than scape, SI 93. Eye a little longer than first flagellomere; OMD 1.25 x EL. Lateral ocelli slightly larger than anterior ocellus; IOD 3.0 x OD; OOD 3.3 x OD. Mandible septendentate. Penultimate segment of maxillary palp broadest in middle, more narrowed apically than basally; fourth segment strongly clavate, preapical width more than twice basal, outer margin nearly straight, inner strongly sinuate.

Thorax: Robust, PW 0.61-0.65 x WL. Posterior half of mesoscutum flattened and continuous with anterior half of scutellum, posterior half of scutellum strongly sloping, flat; metanotum, barely convex in profile, not protruberant; propodeum with distinct horizontal basal area, abruptly rounded onto posterior face.

Petiole: In profile, sharply cuneate, crest narrow; in frontal view, sides slightly narrowed above, crest deeply, angularly notched; from above, about three times wider than higher.

Vestiture: Clypeus with little or no pubescence; pubescence of frontal lobes short, sparse; malar area with sparse, coarse pubescence near mandibular bases; head otherwise with fine, widely scattered pubescence. Thoracic pubescence longer, sparse on sides of mesoscutum; fine and sparse on pleura; a little denser, coarser and decumbent on propodeum. Gastric sheen pronounced on first tergum, distinctly less developed on second, third and fourth segments.

Malar area with abundant subdecumbent coarse hairs in frontal view (longer hairs from gular area are usually visible in frontal view); cephalic hairs otherwise confined to clypeus, frontal lobes and occiput, longest occipital hairs about 0.5 x MOD. Mesoscutal hairs abundant, but rather sparse, longest hairs about equal to 0.5 x MOD; scutellum with numerous hairs, longest more than 2 x longest scutal hairs; pleura with scattered long, erect hairs, about equally abundant above and below; propodeum with short erect hairs above and on sides. Petiole with short erect hairs on crest and sides. Terga with sparse, short, erect hairs, progressively longer on succeeding segments. Scape with numerous suberect and scattered erect hairs. Fore femur with numerous suberect and sparse erect hairs on inner face; hind femur with sparse, short erect hairs on dorsal face; hind tibia with abundant fully erect and suberect hairs on outer face.

Wing membrane with scattered, very short, fully erect hairs; fringe hairs present, but sparse, on posterior margin of hind wing.

Integument: Clypeus shiny, subpolished, with sparse, coarse punctures; frontal lobes shiny, lightly shagreened, with irregularly spaced, fine punctures; frons shiny, subpolished to polished, with scattered fine punctures; occiput duller, lightly shagreened, with scattered finer punctures; malar area shiny, lightly shagreened, densely and finely punctate below, above with scattered coarse punctures.

Mesoscutum shiny, disc subpolished to polished and with widely scattered coarse punctures; parapsis duller, lightly shagreened, with irregularly spaced, mixed, coarse and fine punctures; scutellum shiny, lightly shagreened, with uniformly spaced coarse setigerous punctures. Propodeum slightly shiny, strongly shagreened. First tergum moderately shiny, with fine, dense, piligerous punctures; second tergum shinier, more sparsely and finely punctate; third tergum similar to second.

Color: Light brownish, gaster a little lighter than head and alitrunk; appendages lighter; mandibles and sides of clypeus yellowish.

Type Material
Holotype and paratype workers: 1.9 mi N Thousand Palms, 190', Riverside Co., CALIF., 5 Feb. 1967 (R. R. Snelling). Holotype and most paratypes in ; three paratypes each in, ,.

Etymology
Tenuis (L., thin) + nodus (L., knot), because of the thin petiolar node as viewed in profile.