Myrmecocystus mendax

A diurnal foraging species, with workers that are active scavengers of dead arthropods and predators of living arthropods.

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

Key to Myrmecocystus subgenus Endiodioctes species.

Worker - HW 0.9-1.9 mm; malar area with numerous erect hairs; longest hairs of pronotum and disc of second tergum of large workers at least 0.6 x MOD, usually longer; long pronotal hairs gradually tapering to tip which is not conspicuously curled, but may be gently curved. Female - Apparently inseparable from that of melliger. Male - Apparently inseparable from those of Myrmecocystus melliger and Myrmecocystus placodops. (Snelling 1976)

Distribution
United States, Mexico. Central Colorado south to Texas, west to desert mountain ranges of southeastern California; adjacent northern Mexico.

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



Biology
Snelling (1976) - Wheeler (1908) reported briefly on the type colony of mendax. Sexual forms were found emerging and taking flight at 4:10 P. M. following a rain shower. On the following day the nest was excavated. Since repletes were not found, but insect fragments were found in some chambers, Wheeler concluded the species to be carnivorous.

Colonies in Colorado were reported on by Gregg (1963), who found that crateriform tumuli mayor may not be present. Nests may be situated beneath stones and there is apparently a preference for clay soils. He found the species at elevations ranging from 3600-6600', in the Upper Sonoran, mostly in Pinon-Cedar Woodland and Short Grass Prairie. Texas records include Pinon-Oak Savannah and Mesquite-Acacia Savannah. In other states it has been taken in Pinon-Juniper Woodland, Grama-Tobosa Shrubsteppe and Oak-Juniper Woodland.

The foraging behavior is much as that of Myrmecocystus melliger. Foraging is diurnal and the workers are active scavengers of dead arthropods and predators of living arthropods. Foragers of the colony observed near Wimberley, Texas, were seen to bring seven medium-sized (up to 25 mm) lepidopterous larvae in a period of 20 min. Other prey included one freshly killed muscoid fly, one dessicated muscoid and several fragments from an acridid, apparently recently dead. That workers also gather nectar and/or honeydew is attested by the presence of repletes in nests studied in Texas and Arizona.

The ant cricket Myrmecophila nebrascensis Lugger has been found in one nest observed 8.1 mi SE Sunnyside, Cochise Co., Arizona.

Wheeler observed a mating flight of this species at Mt. Washington, Colorado on 18 July 1903, already mentioned above. A flight was observed by Creighton in the Baboquivari Mts., Arizona, on 26 July 1951. His notes state simply. . . "Both queens & males present. They take no notice of each other and take off singly. The usual excitement among the workers." There had been a thunder shower about noon of the day before.

Nomenclature

 *  mendax. Myrmecocystus melliger subsp. mendax Wheeler, W.M. 1908d: 351, fig. 4 (w.q.m.) U.S.A. Raised to species: Creighton, 1950a: 445. Senior synonym of orbiceps: Snelling, R.R. 1976: 35.
 * orbiceps. Myrmecocystus melliger subsp. orbiceps Wheeler, W.M. 1908d: 349, fig. 3 (w.q.) U.S.A. Junior synonym of melliger: Creighton & Crandall, 1954: 2; of placodops: Snelling, R.R. 1969a: 6; of mendax: Snelling, R.R. 1976: 35.

Snelling (1976) - Although orbiceps has page priority over mendax, I have chosen, as first reviser, to continue usage of mendax. The name orbiceps has been the object of a singularly calamitous history and to resurrect it would only create further confusion. The name has been in synonymy for twenty years and is, in my opinion, best left there.

Wheeler (1908) described orbiceps as a subspecies of melliger characterized by the presence of workers with orbiculate heads and the absence of repletes. He had numerous specimens available from Texas, New Mexico and Arizona; the type series was from Bull Creek, near Austin, Texas. His description and figures leave no room for doubt as to the identity of the insect being described. On a subsequent page of the same paper mendax was adequately described, also as a subspecies of melliger.

In the years following, the concepts of these forms remained fairly consistent although Creighton (1950) predicted that orbiceps would ultimately be shown to be a synonym of melliger. The conceptual melliger, as established by Wheeler and Creighton was not the same as Forel's ant; it was, in fact, misidentified samples of orbiceps in which there were no workers with orbiculate heads, but did include some material of mendax. Creighton and Crandall (1954), reporting a monumental nest excavation by Crandall, were able to show that the form with orbiculate heads did, indeed, produce repletes. They therefore placed orbiceps in synonymy with melliger.

Snelling (1970) reviewed the melliger group species. The concept of Myrmecocystus melliger, based on an examination of Forel's types, was clarified and Wheeler's comatus placed in the synonymy of that form and the status of Myrmecocystus mendax, as a valid species, was somewhat clarified. There is, however, no excuse for his treatment of orbiceps, for that name was placed in the synonymy of Forel's Myrmecocystus placodops. Type material of both was at hand for direct comparison, but no such comparison was made, simply because the concept as to the identity of orbiceps was exceptionally clear and it was obvious that placodops fits that concept perfectly.

It was with considerable chagrin, therefore, that I discovered that the types of orbiceps are not "orbiceps" at all. They no more match Wheeler's description and figures of orbiceps than does the long-haired variant of mendax. In fact, they are the long-haired variant of mendax. Wheeler apparently wrote up his description and then selected his best set of specimens as types and never realized that they were not conspecific. The subsequent identity of orbiceps has been based on the concept created by the description and figures, a concept which could not include the types. Because of the confused identity of orbiceps and because of the inappropriate nature of that name to the present species, I feel that continued use of mendax is fully justified.

This species is very closely related to both Myrmecocystus melliger and Myrmecocystus placodops. Erect body hairs are subject to much variation through the entire range of the species and have been a source for confusion in the past and for frustration to the present writer.

Samples from Colorado, northern New Mexico and Arizona, Nevada and California differ greatly from those of Texas and southern New Mexico and Arizona. In large workers of the northern, short-haired form, the longest hairs of the pronotum are 0.58-0.60 x the MOD and the longest discal hairs of the second tergum are about 0.65-0.68 x the MOD. From the Edwards Plateau of central Texas to the mountains of southern Arizona a distinctive, long-haired form predominates, but does not wholly replace "normal" mendax. In the large workers of this form, hairs are shortest in samples from the Edwards Plateau. The longest pronotal hairs are 0.70-0.75 x the MOD and the long discal hairs of the second tergum 0.75-0.80 x the MOD. Westward from the Edwards Plateau, hair length increases to an extreme condition present in samples from the mountains of southern Arizona. Here the pronotal hairs may be up to 1.30 x the MOD and the discal hairs of the second tergum up to 1.15 x the MOD.

Much the same situation applies in a north to south cline, for, distinctive as these extreme short-haired and long-haired forms are, they are perfectly intergradient to one another. There is no question, in my mind, of two species being represented, nor that the southern form can be set up as a subspecies: the cline is too fully developed. Furthermore, in the mountains of southern New Mexico and Arizona there are nests in which all, or most, of the larger workers are much more like the northern form. A single sample is available from Chihuahua (Nogales Ranch, Sierra de en Medic). In the large workers the long pronotal and discal hairs of the second tergum are 0.65 x the MOD. The single specimen from Cananea, Sonora, is a medium-sized worker but appears to be of the short-haired form, as seems true of the small workers from Puerto Gonzalitos.

The closely related species [[Myrmecocystus placodops, which ranges from western and southern Texas to southern Arizona, is a short-haired ant. It is broadly sympatric with mendax. Workers differ most conspicuously from those of Myrmecocystus mendax in the shorter hairs; in large workers, the long pronotal hairs are about 0.46-0.48 x the MOD, as are those of the second tergum. There appears to be little variation in this regard in placodops, western populations being very similar to those of Texas in hair length.

The great range of variation noted for mendax was very troublesome, especially since it closely approached the accentuated hair length of melliger. It became evident, finally, that those populations of mendax with long hair were those adjacent to, or sympatric with, the closely related placodops. I can only hypothesize that mendax is exhibiting character displacement against placodops.

As I interpret the situation, mendax and placodops may both be derived from a form very much like the present Myrmecocystus melliger. I also assume that placodops diverged at an earlier period and is now genetically more stable than Myrmecocystus mendax. The short-haired condition of mendax appears to be inhibited in those areas where it is adjacent to, if not actually sympatric with, placodops. Interestingly, the few specimens from northern Mexico, in areas where the range of mendax becomes sympatric with melliger, show an apparent reversal of the longhaired trend in mendax. In these, displacement against melliger produces short-haired mendax. Clearly, more field work must be done, particularly in northern Mexico. An effort should be made to delimit areas of melliger-mendax sympatry and to study the populations of these areas.

There has been some confusion in the past of the long-haired variant with comatus, a synonym of meltiger. The New Mexico records cited by Cole (1954) and those from Colorado in Gregg (1963) as comatus are based on long-haired populations of mendax. Even more remarkable, perhaps, is the record of mendax from Hidden Springs Canyon, San Bernardino Co., Calif., recorded as Formica subpolita camponoticeps Wheeler by Cook (1953). This is merely another example of that author's complete lack of taxonomic ability.

Worker


Snelling (1976) - Measurements. HL 1.10-1.97 (1.65); HW 0.93-1.92 (1.55); SL 1.37-2.24 (1.90); WL 1.8-3.3 (2.5); PW 0.7-1.4 (1.1).

Head: Distinctly longer than broad to slightly broader than long, CI 85-1 03 (94), distinctly shorter than scape, SI 110-132 (118); in frontal view, sides straight and hardly narrowed toward mandibular insertions (small workers) to gently, evenly convex and distinctly convergent toward mandibular insertions. Occiput, in frontal view, low and gently convex in small workers, flattened in large workers, broadly rounded at sides. Eye small, 1.10-1.15 x first flagellomere; OMD 1.57-2.36 (2.00) x EL. Mandible with seven teeth.

Thorax: Slender to moderately robust, PW 0.350.46 (0.44) x WL. Propodeum, in profile, about as high as long, basal face slightly sloping and broadly rounded into posterior face.

Petiole: In profile, thick, not at all cuneate, summit broadly rounded, but may be flattened, rarely subangulate; crest, in frontal view, usually flat, but may be slightly concave.

Vestiture: (Based on workers with PW in excess of 0.9 mm). Cephalic pubescence general, but sparse, never obscuring integument, most abundant on occiput, vertex and frontal lobes. Sparse on pronotum, more abundant on remainder of thorax, only partially obscuring surface, densest on propodeum. First three terga with conspicuous pubescence, usually notably sparse in small workers; fourth tergum usually not pubescent, except in some large workers of southern populations.

Malar area with 15+ short, erect hairs (sometimes as few as 10 in smallest workers); longest occipital hairs (in large workers) 0.75-1.20 x MOD, hairs curved but not curled, gradually narrowed toward apex; area between eye and frontal lobe with numerous short, erect hairs. Pronotal hairs abundant, often somewhat curved but not curled at apex, gradually tapering to apex, longest hairs 0.75-1.1 x MOD, not exceeding EL; mesonotal hairs shorter, at most 0.6 x MOD; basal face of propodeum with numerous erect hairs, longest 0.7-1.0 x MOD. Petiole with numerous erect hairs on sides and crest, longest not more than 0.5 x MOD, usually less. Abdominal terga with abundant long erect hairs, longest on disc of second tergum 0.9-1.0 x MOD. Scape, all surfaces of femora and tibiae, with abundant short, fine, erect and suberect hairs, longest hairs of hind tibia shorter than maximum width of that segment.

Integument: Head slightly to moderately shiny, lightly shagreened; frontal lobe closely micropunctate and with sparse coarse punctures, punctation more or less obscured by dense shagreening; face, between eye and frontal lobe with abundant obscure micropunctures and scattered coarse punctures; malar area with sparser coarse, shallow punctures; vertex and occiput densely micropunctate and with sparse coarse punctures and a few shallow poriform punctures; punctation extending laterad to sides of head. Thorax slightly shiny, densely shagreened and micropunctate, with sparse coarse punctures; propodeum duller, more densely micropunctate. First two (minor workers) (three in southern populations) or three (major workers) (four in southern populations) terga moderately shiny, closely micropunctate and with sparse shallow poriform punctures.

Color: Head yellowish to brownish ferruginous, often lighter anteriorly; thorax light to medium brownish, pronotum and sides often yellower; gaster medium to dark brownish; legs light to medium brownish; antennae yellowish to reddish brown, apical segments darker.

Queen
Snelling (1976) - Measurements. HL 1.87-2.13; HW 190-2.16; SL 1.83-2.20; WL 4.0-4.8; PW 2.5-3.2.

Head: Slightly broader than long, CI 102-108; in frontal view, sides straight or slightly concave, a little convergent toward mandibular insertions; a little shorter, to a little longer than, scape, SI 95-103. Occiput, in frontal view, slightly convex, broadly rounded at sides. Eye small, 0.93-1.25 x first flagellomere; OMD 1.60-1.73 x EL; 000 4.0-6.0 x OD; IOD 2.4-3.3 x OD. Mandible with seven teeth. Penultimate segment of maxillary palp slender, broadest in basal third, evenly tapered toward apex.

Thorax: Moderately to very robust, PW 0.56-0.70 x WL. Scutum flattened behind; scutellum convex in profile, a little flattened in front. Basal face of propodeum strongly sloping and broadly rounded onto posterior face.

Petiole: In profile, thickly cuneate, more compressed above, summit narrowly rounded; crest, in frontal view, deeply angularly incised.

Vestiture: Cephalic pubescence general but sparse, most abundant on malar area near mandibular base, on frontal lobe and on occiput. Mesoscutum with pubescence general but sparse, absent only from median impunctate area; general but sparse on scutellum. Pronotum, pleura and propodeum much more conspicuously pubescent. First four terga uniformly and closely pubescent.

Malar area with 15+ erect hairs, longest less than 0.5 x MOD; face with sparse, short erect hairs, including area between eye and frontal lobe; longest occipital hairs 0.5-0.7 x MOD (up to 1.0 x MOD in Edwards Plateau populations). Longest mesocutal hairs usually about 0.5-0.6 x MOD, but may be as much as 0.9 x MOD (Edwards Plateau populations), hairs sparse, suberect. Scutellar hairs sparse, longest about 0.9 x MOD (northern) to 0.9 x EL (southern). Longest anepisternal hairs 0.55 (northern) to 1.0 (Edwards Plateau) x MOD; longest katepisternal hairs about 0.6-0.7 x longest anepisternal hairs. Propodeum with sparse erect hairs across base and on side, longest hairs about 0.6 (northern) to 1.0 (Edwards Plateau) X MOD. Petiole with numerous erect hairs on sides and crest. Gastric terga with numerous erect hairs, most of which, on first two segments, arise from coarse poriform punctures; longest hairs on disc of second segment from 0.5 (northern) to 1.0 (Edwards Plateau) x MOD. Scape, femora and tibiae with abundant short, suberect to erect hairs, longest on hind tibia equal to, or slightly exceeding, minimum thickness of tibia. Fore and hind wings without fringe hairs on apical or posterior margins.

Integument: Cephalic integument similar to that of worker but clypeus duller, distinctly shagreened; malar area closely punctate with micropunctures and somewhat ovoid coarse punctures. Mesoscutum densely micropunctate and with sparse coarse punctures over entire disc or with impunctate median area of variable extent; parapsis uniformly, closely micropunctate. Scutellum uniformly micropunctate, interspaces usually greater than a puncture diameter, and with sparse coarse punctures. Anespistemum slightly shiny, densely shagreened, obscurely micropunctate and with scattered coarse punctures; katepisternum duller, densely micropunctate and with sparse coarse punctures. Propodeum dull or slightly shiny, densely shagreened and micropunctate, with sparse coarse punctures on basal face and sides; lower half of posterior face smooth and shiny. First four gastric terga moderately shiny, uniformly densely micropunctate, with sparse, coarse, poriform punctures; no impunctate median areas.

Color: Head and thorax ferruginous; propodeum, petiole and gaster medium to dark brownish; scape ferruginous, flagellum light brownish; legs ferruginous to brownish. Wings slightly brownish, veins and stigma light yellowish brown.

Male
Snelling (1976) - Measurements. HL 0.97-1.10; HW 0.93-1.07; SL 1.17-1.37; WL 2.1-2.6; PW 1.3-1.6.

Head: A little longer than broad to a little broader than long, CI 93-102, distinctly shorter than scape, SI 117-141; in frontal view, sides straight or slightly concave, slightly convergent toward mandibular insertions. Occiput, in frontal view, strongly but evenly convex, slightly angulate at sides. Eye large, OMD 0.75-0.90 X EL; OOD 1.67-2.80 x OD; IOD 2.00-3.20 X OD. Apical margin of mandible usually with low preapical tooth.

Thorax: Robust to very robust, PW 0.49-0.67 x WL. Propodeum without distinct basal face, in profile more or less evenly convex from base to apex.

Petiole: Low, strongly cuneate, summit usually sharp but may be narrowly rounded; crest, in frontal view, narrowed above, distinctly, angularly incised.

Vestiture: Cephalic pubescence dilute, densest on frontal lobes, malar area and occiput. Pubescence short, dilute on pronotum, scutum and scutellum; long, dilute on mesopleura, metapleura and propodeal side; long, denser, across base of propodeum. First three terga conspicuously, but thinly, pubescent; remaining terga with scattered pubescence.

Malar area with 6-10 erect hairs, longest about 0.6 x MOD. Longest occipital hairs about 0.75 x MOD. A few short erect hairs on face between eye and frontal lobe. Longest scutal hairs 0.70-0.80 X MOD; scutellar hairs longer than those of scutum, some 1.0 x EL. Pleural hairs sparse, long, longest 0.9-1.1 x MOD. Long hairs across base of propodeum about equal to MOD. Sides and crest of petiole with numerous short hairs, about 0.5 x MOD. Disc of first tergum, behind summit with erect hairs sparse, those at summit about 0.75 x MOD; disc of second tergum similarly sparsely hairy or wholly apilose, but with usual row along apical margin and with sparse hairs along length at sides, where they are about 0.8 x MOD; apical segments with long hairs abundant, longest exceeding EL. Scape, femora and tibiae with abundant suberect to erect short hairs, longest hairs of hind tibia about equal to apical thickness of tibia. Fore and hind wings without fringe hairs on apical and posterior margins.

Integument: Head moderately shiny, distinctly shagreened, with sparse obscure micropunctures, and a few coarse punctures, occiput duller, more densely and sharply micropunctate. Mesoscutum dull, densely and uniformly shagreened with sparse, obscure micropunctures and scattered coarse punctures; scutellum shinier, less closely tessellate than scutum, with similar punctation. Mesopleura slightly shiny, katepisternum duller and more densely shagreened than anepisternum, both sparsely micropunctate and with scattered coarse punctures. Propodeum shinier than pleura, shagreening less dense, micropunctures equally sparse but more distinct, especially basally; discal area shinier. First two terga slightly shiny, sharply shagreened and sparsely micropunctate, with scattered coarse punctures basally and laterally; remaining terga shinier, less closely shagreened, micropunctures and coarse punctures sparser.

Color: Blackish brown, antennae and legs medium brown. Wings faintly brownish, veins and stigma yellowish brown.

Type Material
Snelling (1976) - An unspecified number of cotypes of all castes from Mt. Washington, near Colorado Springs, Colorado, July 19, 1903 (W. M. Wheeler). Lectotype worker, by present selection, agreeing with above general description and parenthetical data, in ; lectoparatypes, all castes in AMNH,,.

Myrmecocystus melliger subsp. orbiceps: an unspecified number of worker and female cotypes from Bull Creek, near Austin, Texas (Brues, Melander and Wheeler). Lectotype worker, by present selection (HL 1.85, HW 1.85, SL 2.25, WL 2.85, PW 1.25 mm), agreeing with above general description and Edwards Plateau specifics, in AMNH; lectoparatypes in AMNH, LACM, MCZ.