Myrmecocystus semirufus

A diurnal forager that is a scavenger and effective predator.

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

Key to Myrmecocystus subgenus Endiodioctes species.

Worker -Malar area with more than 10 erect hairs visible in frontal view; thorax abundantly hairy, erect hairs of promesonotum uniform in length, none more than 0.5 x MOD; head, thorax and appendages clear ferruginous. Female: Malar area, in frontal view with 10+ erect hairs; thorax exceptionally robust, PW 0.71 x WL; parapsis sparsely, coarsely punctate; median area of first two terga sparsely punctate in contrast to remainder of disc; penultimate segment of maxillary palp broader basally than apically. Male: Scutum and scutellum uniformly densely tessellate; first three terga uniformly densely pubescent and micropunctate; longest occipital hairs stiff, less than 0.50 x MOD. (Snelling 1976)

Distribution
United States. Tulare and Inyo Counties, California south to northern Baja California. Desert mountain ranges.

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

Habitat
Habitats for Myrmecocystus semirufus include California Oakwoods, Pinon-Juniper Woodland, Great Basin Sagebrush Shrub, Creosote bush-Bur sage Shrub and Creosote bush Shrub. Elevation ranges from 400 feet to about 5000 ft. The majority of the records are from the Pinon-Juniper Woodland to Creosote bush-Shrub ecotone. This is approximately equivalent, in the western Mojave Desert, to the Joshua Tree Woodland of Munz (1974).

Biology
Snelling (1976) - Wheeler and Wheeler (1973) reported on this species (as placodops) in Deep Canyon. Within the Desert Biome in Deep Canyon, they found colonies distributed as follows: Larrea-Palo Verde Community, 800' (3); Cholla-Palo Verde Community, 900-1200' (14); Agave-Ocotillo Community, 2500' (1). One colony was located at 3600' in the ecotone between the Desert and Chaparral Biomes. A crateriform tumulus was observed to be about 25 em external diam., inner rim about 15 em diameter, the entrance 20-25 mm diam.

Nests studied near Pearblossom were all situated in deep, but well-packed sand at the edge of a wash, as was the one located south of Big Pine. The one found in Last Chance Canyon was sited at the edge of a road, about 20 feet above the bed of Last Chance Creek. The nests were surmounted by low, broad crateriform tumuli composed of sand particles and fine soil.

As with other species of Endiodioctes, Myrmecocystus semirufus is a diurnal forager and is a scavenger. It is also an effective predator; at Pearblossom, returning foragers were bringing in many recently dead insects, mostly leafhoppers (Cicadellidae) and grass bugs (Miridae), but including a few termites, beetles, flies and small wasps and bees. The quantity of recently dead insects strongly suggests active predation.

During the rainy spring and autumn seasons foragers are also active on flowers. At Pearblossom I have seen them on Malacothrix (Asteraceae), Phacelia (Hydrophyllaceae), Salvia (Lamiaceae), Oenothera and Camissonia (Onagraceae), Mentzelia (Loasaceae) and Cryptantha (Boraginaceae) during March-May; in September and October the workers are found at the flowers of Eriogonum (Polygonaceae) and Haplopappus (Asteraceae). The specimens collected near Tehachapi were noted to be on Isomeris arborea Nutt. (Capparaceae).

Nomenclature

 *  semirufus. Myrmecocystus melliger var. semirufus Emery, 1893i: 667 (w.m.) U.S.A. Wheeler, G.C. & Wheeler, J. 1968: 213 (l.); Snelling, R.R. 1976: 46 (q.). Subspecies of melliger: Wheeler, W.M. 1908d: 355. Raised to species: Creighton, 1950a: 449.

Snelling (1976) - This name has been the subject of considerable confusion, briefly reviewed by Snelling (1969). The original description was based on specimens from San Jacinto, Calif. and Denver and Pueblo, Colo. Wheeler (1908) correctly recognized that two species were represented in Emery's material and restricted the true semirufus to the California sample; the Colorado specimens were assigned to his mendax. Thus, the type locality was restricted to San Jacinto, Calif. And has priority over the designation of Denver, Colo. By Creighton (1950), repeated by Gregg (1963). Cook (1953) cited both as the type locality.

Unfortunately, Wheeler (1908) then incorrectly applied the name to a very different, wide ranging ant which only superficially resembles semirufus. The correct name for semirufus of Wheeler and subsequent authors is Myrmecocystus kennedyi, except for those misidentifications which apply to still other species. The true semirufus is an uncommon species known only from southern California and adjacent Baja California.

Although the females are very different, the workers of this species most closely resemble those of Myrmecocystus placodops and are separable only with difficulty. The records from Deep Canyon by Wheeler and Wheeler (1973) as placodops are based on specimens which I misidentified as that species. In my paper (Snelling 1969) on the melliger group I attempted to separate the two by the broader head and more obscurely punctate frontal lobes of placodops. The result is far from satisfactory, for some workers of Myrmecocystus semirufus do have the head wider than long, though the percentage of such individuals is much lower in semirufus than in placodops. That character, at least, is not to be relied upon.

The sculpturation of the frontal lobes is another matter, and I am forced to rely upon it, even though it is not wholly satisfactory.

In most workers of semirufus the frontal lobes are shiny and the surface is beset with numerous sharply defined, round punctures, the largest of which are about one-third greater than the smallest. The interspaces vary from as little as one-fourth a puncture diameter to slightly more than a puncture diameter. Similar, but more widely spaced, punctures are usually present on the face between the frontal lobe and the eye; these punctures are less sharp than those of the frontal lobes and the interspaces are distinctly tessellate and less shiny. From these facial punctures emerge short (about 0.06 mm long) stiff, erect hairs. The malar area has scattered coarse punctures which are clearly several times greater in diameter than the hairs arising from them. This is, in fact, generally true: the cephalic hairs arise from punctures conspicuously greater in diameter than •the hairs. Between the ocelli of semirufus the surface is closely micropunctate; these punctures extend up onto the occiput, continuing back nearly to the foramen. On the occipital summit they occupy the middle one-third or more of the dorsum.

From the above conditions placodops differs. The surface of the frontal lobes is dull, often very closely tessellate. When punctures are sharp, their presence is greatly obscured by dense tessellation. Often, however, the punctures are shallow and not well defined. The face, between the eye and the frontal lobe is dull, finely tessellate; as a rule, the only punctures present are the micropunctures from which the pubescence emerges. A few coarse punctures may be present near the inner eye margin and in an arc laterad from the top of the frontal lobe.

The erect hairs of the malar area often arise from poriform punctures. Some of the hairs may emerge from punctures which hardly exceed the diameter of the hairs. In large workers the erect cephalic hairs, except those of the clypeus and frontal lobes, may all arise from such poriform punctures. In small workers these punctures may be present on the occiput.

The area between the ocelli is often not micropunctate in placodops. When micropunctures are present, as in semirufus, they usually are limited to the ocellar area. Seldom do they extend back to the summit of the occiput and seldom, or never, approach the foramen. When they are present they usually are found only immediately behind the ocelli, not extending laterad as in semirufus.

The most common variations of semirufus include more tessellate frontal lobes, a sporadic nest variant, weakening of facial punctures (Morongo Valley and some Deep Canyon samples) and weakening of occipital micropunctures (Morongo Valley and sporadic nidovariants elsewhere). In general these cephalic characters, even though they must be studied with care, seem to be the only effective means of separating workers. In color the two are similar, but semirufus often lacks dark areas on the thorax. Some samples, especially those from Deep Canyon and Independence, are fully as dark as placodops.

The distribution of semirufus appears to lie wholly to the west of that of placodops. They may become sympatric in the mountain ranges of the central Mojave Desert.

Worker


Snelling (1976) - Measurements. HL 1.13-1.73 (1.20); HW 1.00-1.72 (1.12); SL 1.40-2.00 (1.53); WL 1.9-2.9 (2.1); PW 0.7-1.3 (0.85).

Head: Usually distinctly longer than broad, rarely slightly broader than long, CI 86-103 (93), distinctly shorter than scape, SI 110-131 (128); in frontal view, sides straight and only slightly convergent toward mandibular insertions to gently convex in large workers. Occiput, in frontal view, flat or very slightly convex, abruptly rounded onto sides. Eye small, 0.90-0.96 (0.90) x first flagellomere; OMD 1.60-2.10 (1.88) x EL. Mandible with seven teeth.

Thorax: Slender to moderately robust, PW 0.370.46 (0.40) x WL. Propodeum, in profile, evenly curved from base to apex, without well defined basal and posterior faces.

Petiole: Thick in profile, not at all cuneate, summit broadly and evenly rounded; crest, from front, flat or slightly concave, without median notch; from above about 1.5 wider than long.

Vestiture: Pubescence moderately dense on vertex and occiput, sparse elsewhere on head; general on thorax, moderately dense, nowhere obscuring surface; dense on first three terga; fourth tergum sparsely pubescent in small workers, moderately pubescent in larger workers.

Malar area with more than 10 short, fully erect hairs; occiput with numerous short, straight, stiff, fully erect hairs, longest 0.59-0.64 x MOD; short, stiff erect hairs general elsewhere on head. Promesonotum with numerous uniformly short, stiff erect hairs, longest 0.5 or less x MOD; propodeum with numerous similar hairs on all except posteriorly sloping face. Petiole with numerous short, erect hairs across summit and along sides. First four terga with abundant short, fine hairs, mostly arising from poriform punctures, longest on disc of second about 0.1 mm. Scape, all femoral and tibial surfaces with abundant short, stiff, suberect to erect hairs.

Integument: Head moderately shiny, lightly shagreened; vertex and occiput closely micropunctate and with sparse coarser punctures; frontal lobes with coarse, close punctures; front of head with scattered coarse punctures, sparser on malar area. Thorax dull, densely shagreened and micropunctate. First three terga closely micropunctate and with scattered coarse punctures; fourth tergum similar to third in large workers, shinier, finely shagreened and with scattered coarse punctures in small workers.

Color: Head, thorax and appendages clear ferruginous, gaster medium to dark brownish; legs sometimes slightly brownish.

Queen
Snelling (1976) - Measurements. HL 1.90; HW 2.00; SL 1.97; WL 4.1; PW 2.9.

Head: A little broader than long, CI 105, sides straight, slightly convergent below; slightly shorter than scape, SI 103. Occiput, in frontal view, gently convex, broadly rounded onto lateral head margins. Eye small, 1.08 x first flagellomere; OMD 1.50 x EL. OOD 4.7 x OD; IOD 3.8 x OD. Penultimate segment of maxillary palp broadest a little beyond base, gradually tapering to apex which is a little narrower than base. Mandible apparently octodentate (a small denticle present between basal and first subbasal teeth on the right mandible of the one specimen studied, absent on the left mandible).

Thorax: Unusually robust, PW 0.71 x WL. Mesoscutum flattened behind, but scutum and scutellum not aligned to same plane. Basal face of propodeum narrow and broadly rounded onto posterior face.

Petiole: Cuneate, summit narrow, flat; crest, in front view, shallowly, angularly incised.

Vestiture: Cephalic pubescence sparse, densest on vertex and occiput and near mandibular base. Pubescence sparse on scutum and scutellum, conspicuous but not dense elsewhere on thorax, long on propodeum and pleura, Mediobasal portions of dorsum of first tergum and mediobasal area of second tergum sparsely pubescent, otherwise first four terga moderately pubescent, pubescence not obscuring surface, thinner along broad middle area of each segment.

Erect hairs general on face, about 16 erect and suberect hairs present on malar area; longest occipital hairs less than 0.65 x MOD. Erect hairs numerous on scutum, longest about 0.50 x MOD; some scutellar hairs much longer, nearly equal MOD; long pleural hairs sparse, longest about 0.65 x MOD; propodeum with numerous shorter hairs on sides and across basal face. Petiole with numerous short, erect hairs on sides and across crest. Erect discal hairs less numerous on segments beyond first tergum than on that segment, these hairs arising from coarse punctures and longest about twice minimum thickness of hind tibia. Scapes, femora and tibiae with abundant suberect to erect hairs; inner face of fore femur with hairs shorter, finer and sparser than elsewhere on that segment. Fore and hind wings with fringe hairs on apical and posterior margins.

Integument: Frons, on either side of middle, shiny, subpolished and impunctate, head otherwise slightly shiny and distinctly shagreened; vertex and occiput closely micropunctate and with sparse coarse punctures; frontal lobes coarsely, closely punctate; side of face with abundant, variably spaced (0.5-3.0 x puncture diameter) coarse punctures; malar area with sparse, coarse elongate punctures which become finer and denser below; clypeus sparsely, coarsely punctate. Mesoscutum shiny, lightly shagreened, almost polished posteromedially, with scattered coarse punctures; parapsis with sparse coarse punctures, separated by 1-3 puncture diameters, micropunctures absent. Scutellum shiny, lightly shagreened; finely punctate, punctures in middle separated by 1-2 puncture diameters, sparser laterad; with scattered coarse punctures. Pronotum, metapleura and propodeum slightly shiny, densely shagreened and micropunctate. Mesopleura slightly shinier, anepisternum anteriorly densely shagreened and with scattered coarse punctures, posteriorly more lightly shagreened and similarly punctate; katepisternum duller, closely micropunctate and with sparse coarse punctures. First tergum, at summit of declivity, with irregularly scattered coarse and micropuntures die are separated by more than a puncture diameter and with sparse coarse punctures; middle of disc shiny, with irregularly scattered coarse and micropunctures which become denser caudad and laterad. Broad median area of disc of second tergum shiny, with sparse coarse and micropunctures which become denser caudad and laterad. Third and fourth terga uniformly closely micropunctate and with scattered coarse punctures.

Color: Head and antennae clear ferruginous; thorax light brownish ferruginous, extensive brown areas on scutum, scutellum and propodeum; legs light brownish ferruginous; gaster medium brown. Wings faintly yellowish, subcostal vein brown, remaining veins and stigma pale yellowish.

Male
Snelling (1976) - Measurements. HL 0.90-1.00; HW 0.83-0.97; SL 1.20-1.23; WL 2.3-2.6; PW 1.4-1.6.

Head: A little longer than wide, CI 93-97, distinctly shorter than scape, Sl 123-133; in frontal view sides straight, distinctly convergent toward mandibular bases. Occiput, in frontal view, evenly convex, abruptly rounded onto lateral margins. OMD 0.90-1.00 x EL; OOD 2.0-2.4 x OD; IOD 2.8-3.0 x OD. Mandible without preapical notch or subbasal denticles.

Thorax: Robust, PW 0.57-0.62 x WL. Propodeum, in profile, broadly curved from base to apex, without defined basal face and posterior face.

Petiole: In profile, thick, cuneate, summit broadly rounded; crest, in frontal view, slightly concave in middle; from above, about twice wider than long.

Vestiture: Cephalic pubescence extremely dilute, conspicuous only on occiput. Thoracic pubescence extremely dilute over most surfaces, sparse even on pronotum and propodeum where it is most conspicuous. First three terga with sparse pubescence, fourth with only a few hairs.

Cephalic hairs general, stiff, about 8 on malar area, longest about 0.5 x MOD; longest occipital hairs less than 0.5 x MOD. Thoracic hairs stiff, abundant, longest about 0.5 x MOD, a little shorter across base of propodeum. Hairs of crest of petiole slightly longer, slender and acuminate. Hairs of first three terga short, less than 0.5 x MOD, more slender than those of mesoscutum. Scape, femora and tibiae with numerous suberect to erect hairs. Fore wing without fringe hairs; hind wing with a few hairs on posterior margin in basal half.

Integument: Head slightly shiny, densely shagreened and with sparse coarse punctures, occiput and malar area closely micropunctate. Scutum slightly shiny, densely shagreened, sometimes with traces of shinier area on midline; scutellum similar; pronotum and propodeum barely shiny, densely shagreened and closely micropunctate; pleura similar but without micropunctures; entire thorax with scattered coarse punctures. Gaster slightly shiny, closely shagreened and micropunctate.

Color: Blackish brown, mandibles, antennae and legs light brown. Wings whitish, subcostal vein brownish, remaining veins nearly transparent apicad, becoming pale ferruginous basad.

Type Material
Snelling (1976) - Originally described from workers from Calif. (San Jacinto) and Colo. (Denver and Pueblo); Wheeler (1908) restricted the type locality to San Jacinto, Calif. At least one specimen from San Jacinto is in the Museo Civico, Genoa, Italy, but not available for study. Another worker, marked as cotype, is in the and here selected as Lectotype. Other San Jacinto specimens from the same series, but not originally seen by Emery, are in the.