Myrmecocystus wheeleri

Myrmecocystus wheeleri has been observed foraging during the day.

Identification
A member of the kennedyi group of the Myrmecoystus subgenus Endiodioctes.

Key to Myrmecocystus subgenus Endiodioctes species.

Snelling (1976) - Uniformly orange-ferruginous, rarely legs and gastric apex brownish; longest occipital hairs about equal to EL, longest pronotal hairs about 0.5 x MOD; third tergum densely pubescent; tibial hairs mostly decumbent. Female: penultimate segment of maxillary palp more than twice as wide in basal third as at apex; thorax and gaster extensively ferruginous. Male: ventral lobe of aedeagus concave in profile, coarsely serrate.

Although workers of wheeleri are usually wholly orange-ferruginous there are some samples in which legs and the apical gastric segments may be brownish, especially in minor workers. Such specimens are common in material collected at Little Rock Dam. Since the basal gastric segments may be yellowish in occasional specimens of Myrmecocystus flaviceps and Myrmecocystus kennedyi, and are normally so colored in Myrmecocystus kathjuli, other means of separation must be used. The presence of abundant pubescence on the third tergum will immediately separate Myrmecocystus wheeleri from kennedyi. The occipital and pronotal hairs are much shorter in kennedyi than in wheeleri and the tibial hairs are suberect to erect rather than decumbent.

The resemblance of flaviceps to wheeleri in pilosity is closer, since both possess abundant pubescence on the third tergum. In flaviceps, however, the tibial hairs are suberect to erect, the pronotal hairs do not exceed 0.5 x MOD and the occipital hairs are not equal to EL.

The most closely related species appears to be kathjuli and workers of the two species are very similar in most features. The pronotal hairs are a little longer in wheeleri, about 0.85-0.90 x MOD, than in kathjuli, about 0.60-0.65 x MOD. In the latter species, the sides of the first two terga are brownish and many of the hairs of the tibiae are suberect to erect.

The very broad segments of the maxillary palp and largely ferruginous gaster will immediately separate the female of Myrmecocystus wheeleri from all except Myrmecocystus kathjuli. The frontal lobes are uniformly punctate and the punctures separated by less than a puncture diameter in wheeleri; in kathjuli the punctures are very irregularly spaced, with many interspaces of 1-2 puncture diameters. The summit of the first tergum and the discs of the second and third, are uniformly closely micropunctate in wheeleri females. There are extensive impunctate areas on the first tergum, at least, in the kathjuli females seen.

Although male Myrmecocystus are a monotonously similar lot, offering few distinguishing characteristics, that of wheeleri is the proverbial exception. The ventral lobe of the aedeagus, instead of being strongly convex and finely serrate, as in all other species, is concave and coarsely serrate. Otherwise, this sex is very similar to that of kathjuli but with shorter body hairs.

Distribution
United States. Central California to Baja California (presumably), dry coastal valleys and desert margins.

This taxon was described from the United States.

Habitat
California Steppe, Saltbush-Greasewood Shrub, California Oakwoods, Chaparral, Coastal Sagebrush Shrub, Juniper-Pinyon Woodland and Creosote bush-Bur sage Shrub.

Biology
Snelling (1976) - This ant has been collected near sea level (Pt. Lorna) to about 4000 feet in the San Jacinto Mts. It ranges from arid and semiarid regions of the San Joaquin Valley southward in dry coastal canyons and inland valleys and enters the western margins of the Mojave and Colorado Deserts.

Mallis (1940) described the crateriform tumulus to be about 5 in. diameter, with a single entrance about 0.5 in. diameter, but noted that two days later the same nest had two entrances about 1 in. apart. His observations were made near Bakersfield; the ants were seen to forage at midday and to move rapidly over the sand.

The Wheelers (1973) found that one nest which they observed in Deep Canyon was in exposed sandy soil and surmounted by a "shallow irregular earthworks 9 x 13 inches" with "... several irregular entrances ..." Exoskeletal fragments of arthropods, mostly ants, were in the refuse pile.

A worker was seen by Mallis (1940) bringing the abdomen of a honey bee to the nest. Arthropod remnants are abundant in the refuse piles of Myrmecocystus wheeleri, as already noted by the Wheelers. Head capsules of other ant species are often abundant, especially those of Pogonomyrmex, other Myrmecocystus and Formica. Since I've never seen wheeleri attacking other ants, these may be the result of scavenging, rather than predation. Live insects are regularly taken, especially immature cicadellids and small Lepidoptera larvae.

Foraging workers of this ant regularly visit flowers for nectar; they seem to be especially prone to visit species of Eriogonum (Polygonaceae) and prostrate Euphorbia (Euphorbiaceae). Although I have never found repletes in any of the nests I have studied, there is one replete in the material collected by P. Leonard at Pt. Lorna.

Nest founding females have been found in Chaparral areas of southern California in early March after warm rains. The presence of alates in the nests in summer months (6 June and 15 Aug.) suggests that this species also takes advantage of summer and autumnal rains for mating flights.

Nomenclature

 *  wheeleri. Myrmecocystus wheeleri Snelling, R.R. 1971a: 11, fig. 3 (w.q.m.) U.S.A. See also: Snelling, R.R. 1976: 70.

Worker
Snelling (1976) - Measurements: HL 0.93-1.26 (1.26); HW 0.83-1.10 (1.10); SL 1.16-1.60 (1.60); WL 1.6-2.0 (2.0); PW 0.60-0.83 (0.83).

Head: A little longer than broad, CI 81-96 (86), distinctly shorter than scape; SI 130-153 (145). In frontal view, head broadest at, or a little below, the eyes, sides straight or slightly, evenly convex, narrowed slightly toward mandibular insertions. Occiput in frontal view broadly rounded laterally, summit slightly convex or flattened. Eye small, barely longer than first flagellomere; OMD 1.5-2.1 (2.1) x EL. Mandible usually with seven teeth.

Thorax: Slender, PW 0.36-0.43 (0.41) x WL. Basal face of propodeum broadly rounded into posterior face.

Petiole: In profile, about as thick as high, narrowed toward evenly rounded apex; crest evenly convex in frontal view; in dorsal view, node 1.4-1.5 x wider than long.

Vestiture: Appressed pubescence sparse, short, on head, denser on occiput and vertex; distinctly longer and denser on thorax, coxae and femora, petiole and first three gastric terga. Pubescence very sparse or absent from fourth and fifth terga. Erect hairs sparse on head, confined mainly to clypeus, frontal area and occiput, those of occiput distinctly longer than EL, of frons and clypeus variable, but mostly shorter than EL; malar area with scattered erect hairs less than 0.5 x EL. Pronotum with 12-18 erect hairs of irregular length, longest about 0.5 x MOD, a variable number of much shorter hairs on neck; mesonotum with about a dozen erect hairs, less than 0.5 x EL; metanotum usually without erect hairs; propodeum with 12 or more erect hairs of variable length, the longest equal to at least 0.5 x EL. Petiolar scale with 6-10 fine, erect short hairs on crest. Discs of gastric segments with sparse erect hairs, about equal to 0.5 x EL, hairs of tergal margins only slightly shorter than EL. Scape with abundant fine, short suberect hairs on inner and lower faces. Inner face of fore femur without erect hairs except along lower margin, these about as long as those of outer face. Middle and hind tibiae with abundant fine, subdecumbent hairs on all surfaces, these a little shorter than minimum thickness of the tibiae.

Color: Orange-ferruginous, often with lower half of face more yellowish; fourth and fifth gastric segments often infuscate. Rarely most of thorax, gaster and legs infuscate in some minors.

Queen
Snelling (1976) - Measurements. HL 1.8; HW 1.8; SL 1.8; WL 4.0; PW 2.5.

Head: As broad as long, CI 100; as long as scape; SI 100. In frontal view, head parallel-sided, as broad at mandibular insertions as at lower eye level. Occiput rounded laterally, without evident corners, slightly convex in middle. Eye small, 1.3 times length of first flagellomere; OMD 1.6 x EL; IOD 2.5 x OD; OOD 3.5 x OD. Penultimate segment of maxillary palp broadest at basal third, strongly narrowed toward apex.

Thorax: Robust, PW 0.62 x WL. In profile, posterior half of mesoscutum flat, apical margin below level of convex scutellum; scutellum and metanotum forming continuous convex surface.

Petiole: In profile compressed-cuneate, crest sharp; distinctly notched; from above, about three times wider than long.

Vestiture: Pubescence long, notably dense only on first three gastric terga, variably fully appressed to subappressed, especially on head.

Erect hairs present on all parts of face, least abundant on malar area immediately below eyes, and between eyes and ocelli; occipital hairs irregular in length, longest about as long as EL, hairs on frons and clypeus equally variable, but a little shorter. Hairs abundant on thoracic dorsum and sides, highly variable in length, some longer than EL (especially on sides); basal third of propodeum with abundant long hair, apical two-thirds with very short erect hairs, especially toward apex and around gland opening. Crest and sides of petiolar scale with numerous long erect hairs, gastric terga with abundant fully erect hairs on disc, separated by less than their own lengths, mostly about half as long as EL. Fore femur without conspicuous erect hair on inner face. Tibiae with abundant suberect hairs which are about as long as minimum thickness of hind tibia. Scape with abundant suberect, short hairs on outer and lower faces. Forewing without marginal fringe, hind wing fringed on posterior margin.

Integument: Head moderately shiny, lightly tessellate; frontal lobes with close, fine punctures of variable size, round to ovoid, separated by about a puncture diameter; malar area more sparsely, coarsely punctate. Center of mesoscutum impunctate, median area laterally with scattered fine punctures, becoming close and more distinct in lateral thirds and apically; anteriorly, median portion with sparse micropunctures; punctures denser and coarser on parapsis. Punctures of scutellum finer than of adjacent portion of scutum, sparse in middle, denser laterad; anepisternum minutely roughened between coarse, close punctures, katepisternum equally coarsely, more closely punctate; metapleura and propodeum similar to lower half of mesopleura. Discs of first two terga finely and densely micropunctate, but with punctures in middle irregularly spaced, some inters paces as much as two or three puncture diameters; third tergum uniformly, densely micropunctate.

Color: Orange-ferruginous, the following brownish: rectangular median mark on anterior half of mesoscutum, broad lateral stripes on posterior four-fifths of mesoscutum, irregular blotch on mesopleura above and irregular blotch on mesepisternum. Apical gastric segments lightly infuscated. Wings whitish hyaline, radial vein and stigma brownish, remainder of veins yellowish.

Male


Snelling (1976) - Measurements. HL 0.86-0.90; HW 0.83-0.90; SL 1.03-1.10; EL 0.30-0.33; WL 2.0-2.2; PW 1.16-1.23.

Head: Margins distinctly convergent toward mandibular insertions; head as broad as long or slightly longer (CI 96-100); distinctly shorter than scape; SI 119-128. OMD 0.80-0.90 x EL. Anterior ocellus 2/3 diameter of lateral ocelli; IOD 2.5-3.0 x OD; OOD 2.5-3.0 x OD. Mandible without basal teeth. Clypeus with short transverse depression below middle.

Petiole: In profile, higher than long, narrowed above, crest convex; in frontal view, evenly convex from side to side, except for vague to prominent median notch; in dorsal view about twice as wide as long.

Vestiture: Erect hairs abundant on body, those of scutellum as long as EL, length elsewhere generally shorter but variable. Erect hairs of hind tibia about as long as thickness of scape. Pubescence sparse on head and thorax, abundant on propodeum and first four terga. Forewing without marginal fringe, hind wing with fringe on posterior margin only.

Integument. Head moderately shiny, lightly shagreened, with very sparse micropunctures and scattered coarse punctures. Malar area with a few very coarse, elongate punctures. Occiput duller, more closely micropunctate. Mesoscutum moderately shiny, sharply shagreened and with scattered coarse punctures. Scutellum shinier, less sharply shagreened, with scattered coarse punctures. Mesopleura slightly shiny, very densely shagreened, with scattered coarse punctures. Propodeum similar, but with shinier midline posteriorly. Summit of first tergum shiny and very sparsely punctate in middle; sides of summit of first tergum, entire second and third terga, moderately shiny, closely and uniformly micropunctate.

Color: Uniformly blackish, appendages light brownish.

Type Material
Snelling (1976) - Holotype worker, allotype male, 193 worker and two female paratypes, 6 mi SE of Pearblossom, 3500', Los Angeles Co., Calif., 15 August 1965 (R. R. Snelling). Holotype, allotype and most paratypes in ; additional paratypes in, GCW, , , and.

Etymology
This ant is dedicated to the late William Morton Wheeler, whose career included the first comprehensive study of these remarkable ants.

Determination Clarifications
Snelling (1976) - This ant has been erroneously identified by Wheeler (1908, 1912) as Emery's Myrmecocystus testaceus. The specimens from Phoenix, Arizona, thought by Wheeler to be transitional between this ant and "semirufus" (i.e., Myrmecocystus kennedyi) are actually Myrmecocystus romainei.