Myrmecocystus mimicus

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

Key to Myrmecocystus subgenus Endiodioctes species.

Worker - Malar area with fewer than ten erect hairs, usually on lower half only; frons and vertex smooth, shiny, with little or no pubescence; third tergum with sparse pubescence only; pronotal hairs short, stiff, blunt. Female - Malar area with few or no standing hairs; first three terga uniformly, densely micropunctate; parapsis variably bipunctate; punctures of vertex sparse; alitrunk brownish ferruginous. Male - First three terga smooth, shiny, without conspicuous pubescence; mesoscutum polished and shiny, at least in part; parapsis densely shagreened and micropunctate; pleural hairs at least 0.11 mm long; wings without fringe hairs. (Snelling 1976)

Distribution
United States, Mexico. Southwestern Kansas south to Big Bend region of Texas and north-central Mexico, west to Baja California and California.

This taxon was described from U.S.A.

Biology
Snelling (1976) - This widely distributed species occurs in a variety of habitats, including the following; Pinon-Juniper Woodland, Oak-Juniper Woodland, Coastal Sagebrush Shrub, Great Basin Sagebrush Shrub, Saltbush-Greasewood Shrub, Creosote bush-Bur sage Grassland, Creosote bush- Tarbush Grassland, California Steppe, Grama-Galleta Steppe, Grama-Tobosa Shrubsteppe, Trans-Pecos Shrub Savannah, and Grama-Buffalo grass Grassland. In southern California the altitudinal range is from sea level to about 4,000 feet.

Mating flights most frequently take place in late afternoon following a soaking rain, but morning flights do occur. According to Wheeler (1917) incipient colonies of this species are pleometrotic, an observation I have never been able to confirm. Although I have discovered numerous founding females, all were in individual burrows. Nor, in the many nests studied, have I ever discovered more than a single fertile female in any of these. Pleometrosis, if it does occur in this species, must be very uncommon.

The brief notes published by Wheeler (1908) are based on more than one species, as he had confused Myrmecocystus depilis and Myrmecocystus romainei with mimicus. The nests are commonly located in pebbly or clayey soil, with the latter apparently preferred. Although Wheeler described the tumuli as "... regular craters 10-15 em. across at the base and 3-4 em. high ..." his Fig. 13 shows a simple hole in adobe soil with the excavated material thrown out in a low, irregular crescent. In my own experience the usual condition is well illustrated in that photograph. Regularly crateriform tumuli sometimes are constructed, but they are rare. Often, the entrance is concealed in a dense clump of grass, with the excavated soil cast up about the clump in a manner reminiscent of the irregular superstructures of some Lasius and Formica. This is the only Myrmecocystus studied which commonly has the entrance concealed in a grass clump.

This is a diurnal species, foraging most actively during the middle part of the daylight hours. As with all species of Endiodioctes, Myrmecocystus mimicus is a general scavenger. It avidly visits flowers for nectar and has been observed in attendance on aphids. Repletes of this ant were recorded (as lomaensis) by Wheeler (1912) from Pt. Lorna, California, and I have taken them from nests in various states.

Nomenclature

 *  mimicus. Myrmecocystus melliger subsp. mimicus Wheeler, W.M. 1908d: 353 (w.q.m.) U.S.A. Wheeler, G.C. & Wheeler, J. 1968: 213 (l.). Raised to species: Creighton, 1950a: 446. Senior synonym of lomaensis and material of the unavailable name jesuita referred here: Creighton, 1950a: 447; Snelling, R.R. 1976: 54.
 * lomaensis. Myrmecocystus melliger subsp. lomaensis Wheeler, W.M. 1912d: 175 (w.q.) U.S.A. Junior synonym of mimicus: Creighton, 1950a: 447; Snelling, R.R. 1976: 54.

Snelling (1976) - The type series of this ant, from Albuquerque, New Mexico, is mixed. It includes workers of Myrmecocystus romainei. I have seen none of the six males mentioned by Wheeler as part of the type series; the brief description of that caste would apply equally well to either species.

In selecting a Lectotype for this species I have been guided by expediency. The use of this name has been more or less uniformly applied since 1908. In 1950 Creighton placed var. jesuita and melliger subsp. lomaensis in synonymy with mimicus. I have chosen as Lectotype, therefore, a specimen which supports these interpretations. The alternative would have been to transfer the name to a wholly different species (romainei of this revision) and to resurrect jesuita for the species long known as mimicus. The former choice is least confusing.

The synonymy of jesuita was adequately discussed by Creighton. It is sufficient here merely to state that jesuita is the same as mimicus in the sense of the present study. When Wheeler (1912) described lomaensis he treated it as a subspecies of Myrmecocystus melliger. The characteristics by which it was to be separated from mimicus, also regarded as a subspecies of melliger, will not hold, as correctly noted by Creighton. However, it should be observed that there are differences between the California form and that of New Mexico and Texas. In both males and females of the eastern populations, the hairs of the mesopleura are uniformly quite short and well separated. The mesopleural hairs in the California populations are variable in length, many hairs up to 0.23 mm long, about twice the length seen in specimens from New Mexico and Texas.

Also noticeable in the sexual forms is relatively smaller eye size. Among the western females the malar area is 1.50-1.58 x the EL; in females from Arizona and New Mexico, the range is 1.10-1.43. A similar situation exists among the males studied: 0.78-0.84 in those from California, 0.70-0.75 in those from eastern parts of the range.

The population differences noted are not confined to the males and females, but they are more obvious in these castes. Western workers (lomaensis) do differ from their eastern counterparts. In these, the frontal lobes are more extensively and more abundantly punctate; the punctures extend well up onto the frons and they are mostly separated by two puncture diameters or less. In specimens from New Mexico and Texas the punctures do not extend onto the frons and the intervals between punctures are three to six times a puncture diameter. There is also a tendency among larger workers, in some California samples, to possess more abundant pubescence on the third tergum than is normal. Some samples from the area around Rodeo, New Mexico, are similar.

These differences are interesting, but difficult to interpret. They may represent another example of character displacement. In this case the species displacing against mimicus may be the closely related, and broadly sympatric, Myrmecocystus depilis. Over the broad area of sympatry, from southern Arizona to western Texas, both sexes of depilis are recognizable from those of mimicus by the much longer pleural hairs, up to 0.25 mm long in the females.

It is also possible that the western populations may represent a very closely related species, or, less likely, a subspecies. Before any conclusion can be reached, much additional material, with particular emphasis on the sexual forms, will have to be studied. Such material is not now available.

Worker
Snelling (1976) - Measurements. HL 0.95-1.67 (1.20); HW 0.80-1.57 (1.20); SL 1.03-1.70 (1.30); WL 1.52.6 (1.8); PW 0.6-1.2 (0.8).

Head: Longer than broad to as broad as long, CI 82-100 (100), slightly shorter than to distinctly longer than scape, SI 97-118 (108); in frontal view, margins straight and slightly convergent toward mandibular base (smaller workers) to distinctly convex and abruptly narrowed below (largest workers); occiput, in frontal view, gently convex in smallest, to flattened in largest, workers, broadly rounded laterally. Eye small, 0.9-1.1 x first flagellomere; OMD 1.34-1.90 (1.83) x EL. Mandible with seven teeth.

Thorax: Moderately robust, PW 0.39-0.47 (0.46) x WL. Propodeum, in profile, higher than long, basal face short and moderately to broadly rounded into posterior face.

Petiole: Scale thick, weakly cuneate, summit broadly rounded, rarely distinctly wedge-shaped; crest, in frontal view, usually evenly rounded, but may be flattened or with a narrow, shallow median notch. Vestiture: Pubescence sparse to scattered on head, but often noticeable on vertex and occiput; light to moderately abundant on alitrunk; abundant on first two terga, scattered or absent on third; rarely conspicuous on third, but if so, much less dense than on second.

Malar area, in frontal view, with 2-4 erect hairs near base of mandible, occasionally 2 or 3 more hairs between this group and lower eye margin; longest occipital hairs little, if any, more than 0.5 x MOD; pronotal hairs usually slightly shorter; shorter hairs conspicuous on rest of dorsum; sides and crest of petiolar scale with numerous short, erect hairs; discs of terga with abundant short, erect hairs, uniform in length on first three terga, longer beyond; sterna with hairs long, sparse. Scape, femora (including extensor surface) and tibiae with abundant short, erect hairs.

Integument: Head shiny, lightly to hardly shagreened; frontal lobe with fine punctures separated by a diameter or more; frons and vertex with scattered fine punctures; malar area more distinctly shagreened, with scattered fine punctures. Thorax moderately shiny, lightly shagreened and closely micropunctate. First two terga moderately shiny, lightly shagreened, closely micropunctate; third tergum shinier, more lightly shagreened, nearly impunctate, often polished.

Color: Head, alitrunk and appendages light to dark brownish ferruginous, rarely pale ferruginous; gaster blackish-brown.

Queen
Snelling (1976) - Measurements. HL 1.80-2.00; HW 1.90-2.05; SL 1.60-1.90; WL 3.5-4.4; PW 2.3-2.7.

Head: Sides straight, slightly convergent toward mandibular insertions; head slightly longer than broad to slightly broader than long, CI 97-110; slightly to distinctly longer than scape, SI 84-98. Occiput, in frontal view, evenly arched, without, or with barely perceptible, lateral angle. Eye moderately large, 1.17-1.45 x first flagellomere; OMD 1.10-1.58 x EL; OOD 3.0-5.8 x OD; 100 2.2-4.0 x OD. Penultimate segment of maxillary palp slightly wider at base than at apex, margins evenly convergent from base to apex. Mandible with seven teeth.

Thorax: Moderately to very robust, PW 0.58-0.69 x WL. Scutum and scutellum strongly flattened. Propodeum with well-defined horizontal basal zone.

Petiole: In profile, compressed-cuneate, apex narrowly rounded; crest, in frontal view, weakly to strongly angularly incised in middle.

Vestiture: Pubescence very diffuse on front of head, denser on occiput and malar area, distinctly longer on malar area than elsewhere on head. On thoracic dorsum, pubescence sparse, conspicuous only on parapsis and scutellum; longer and denser on sides and propodeum. Dense on first four terga, imparting distinct sheen.

Malar area with 1-4 suberect to erect hairs on lower half in frontal view, rarely 1 or 2 on upper half; longest occipital hairs 0.5 or less x MOD, rarely slightly longer. Longest mesoscutal hairs much less than 0.5 x MOD (eastern populations) or exceeding 0.5 x MOD (western populations); longest scutellar hairs subequal to MOD; pleural hairs less than 0.5 x MOD (eastern populations) or about equal to 0.5 x MOD (western populations). Propodeum with numerous erect hairs on base and side, longest in western populations. Crest and side of petiole with numerous short, erect hairs. First four terga with numerous fine erect hairs, on second segment up to 0.16 mm in eastern populations and up to 0.12 mm in western populations; longer on last segments and on sterna. Appendages with numerous decumbent to fully erect, short hairs, usually absent from posterior surface of scape; inner face of fore femur with short, suberect hairs abundant on distal half only. Wings without marginal fringes.

Integument: Clypeus slightly to moderately shiny, with sparse, coarse punctures; frontal lobes finely punctate in middle, conspicuously more coarsely and sparsely punctate toward margins; malar area with coarse, close, ovoid punctures; front of head coarsely, sparsely punctate, but with narrow to broad impunctate (or nearly so) band between eye and ocellar area; occipital punctures fine, dense. Disc of scutum shiny, with scattered coarse punctures, parapsis finely and densely punctate (punctures may be more separated adjacent to parapsidal line); scutellum uniformly closely and finely punctate. Anepisternum dull to moderately shiny, with close, coarse, ovoid punctures and scattered coarser, round punctures. Katepisternum usually duller, more finely and closely punctate. Propodeum dull, minutely roughened, closely and very finely punctate. Summit of first tergum densely micropunctate; discs of second and third terga similar to first.

Color: Head and thorax dark reddish brown to medium brownish, gaster blackish; appendages lighter. Wings slightly whitish, veins and stigma yellowish to light brownish.

Male
Snelling (1976) - Measurements. HL 0.80-1.00; HW 0.77-0.97; SL 0.87-1.07; WL 1.7-2.2; PW 1.1-1.3.

Head: A little longer than broad to a little broader than long, CI 95-104, shorter than scape, SI 104-112; in frontal view, occiput evenly convex, without perceptible lateral angle; sides straight, evenly and distinctly convergent toward mandibular bases. OMD 0.70-0.84 x EL; OOD 2.0-3.2 x OD, IOD 1.7-2.8 x OD). Mandible without pre-apical notch, usually without pre-apical teeth, but rarely with one or two low denticles.

Thorax: Robust, PW 0.55-0.64 x WL. Propodeum, in profile, strongly sloping and without discrete basal face.

Petiole: In profile, cuneate, summit sharp; in frontal view, crest distinctly notched.

Vestiture: Pubescence everywhere sparse and inconspicuous, a little more abundant on pleurae and across base of propodeum.

Erect hairs sparse and short on head, those of occiput less than 0.5 x MOD. Scutal hairs even in length, longest less than 0.5 x MOD; scutellar hairs a little longer than those of scutum. Pleural hairs conspicuously longer, many exceeding 0.5 x MOD. Propodeum with short, erect hairs on side and across base. Petiole with short, erect hairs on crest and sides. Terga with hairs short and sparse on basal four segments, longer and more abundant on remaining; longer on sterna. Scape, femora and tibiae with numerous short, suberect to erect hairs. Forewing without fringe hairs; hind wing with fringe hairs on posterior margin.

Integument: Head moderately shiny, lightly shagreened, more densely so on malar area, with scattered fine, obscure punctures. Disc of mesoscutum shiny, lightly shagreened, with subpolished area on posterior portion on either side of midline; parapsis less shiny, more distinctly shagreened, punctures scattered, minute. Scutellum shiny to polished, with scattered fine punctures. Pleura moderately shiny, densely shagreened and with scattered fine, obscure punctures. Propodeum moderately shiny and densely shagreened, but may have subpolished median area. First three terga shiny and lightly shagreened to subpolished and barely shagreened and with scattered micropunctures.

Color: Blackish brown, appendage lighter. Wings whitish, veins and stigma yellowish to brownish yellow.

Type Material
Snelling (1976) - Lectotype worker, by present designation and agreeing with above general description and parenthetical data: Albuquerque, New Mexico, May 1905 (W. M. Wheeler) in. Lectoparatypes in AMNH,, and.

M. melliger mimicus var. jesuita: Lectotype worker, by present designation, agreeing with above general description (HL 1.50; HW 1.40; SL 1.55; WL 2.3; PW 1.0; CI 93; SI 102): Ft. Davis, Texas, 8 June 1902 (W. M. Wheeler) in AMNH. Lectoparatypes in AMNH, LACM, MCZ and USNM.

M. melliger subsp. lomaensis: Lectotype worker, by present designation, agreeing with above general description (HL 1.60; HW 1.55; SL 1.55; WL 2.4; PW 1.1; CI 97; SI 97): Point Lorna, Calif. (P. Leonard) in AMNH. Lectoparatypes in AMNH, MCZ, USNM.

Additional References

 * Holldobler, B., Grillenberger, B. & Gadau, J. 2011. Queen number and raiding behavior in the ant genus Myrmecocystus (Hymenoptera: Formicidae). Myrmecological News, 15, 53-61.