Myrmecocystus romainei

AntWiki - Where Ant Biologists Share Their Knowledge
Jump to: navigation, search
Myrmecocystus romainei
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Hymenoptera
Family: Formicidae
Subfamily: Formicinae
Tribe: Lasiini
Genus: Myrmecocystus
Subgenus: Endiodioctes
Species group: romainei
Species: M. romainei
Binomial name
Myrmecocystus romainei
Snelling, R.R., 1975

Myrmecocystus romainei casent0005886 profile 1.jpg

Myrmecocystus romainei casent0005886 dorsal 1.jpg

Specimen labels

Some populations are known from areas with deep, fine sands.

Identification

A member of the romainei group of the Myrmecoystus subgenus Endiodioctes.

Key to Myrmecocystus subgenus Endiodioctes species.

Worker - In frontal view, malar area with 5-17 hairs extending beyond margin; HW not exceeding 1.55 mm; frons and vertex finely and closely punctate; longest occipital hairs less than 0.5 x MOD. Female - malar area with numerous erect hairs; parapsis finely and closely punctate; first three terga uniformly, densely micropunctate; frons abundantly punctate. Male - ventral lobe of aedeagus convex; mesoscutum and scutellum faintly tessellate, shiny; summit of petiolar scale distinctly incised; first two terga without obvious pubescence except at sides, discs smooth and polished; mesoscutal and occipital hairs less than half minimum eye diameter. (Snelling 1976)

Keys including this Species

Distribution

United States. Western Kansas, Oklahoma and Texas, westward to Utah and central Arizona.

Distribution based on Regional Taxon Lists

Nearctic Region: United States (type locality).
Neotropical Region: Mexico.

Distribution based on AntMaps

AntMapLegend.png

Distribution based on AntWeb specimens

Check data from AntWeb

Habitat

Habitats in which this species has been collected included: Bluestem-Grama Prairie, Pinon-Juniper Woodland, Trans-Pecos Shrub Savanna and Creosote bush-Tarbush Grassland. A series from Selden, Kansas, was taken from a "road side nest."

Biology

Snelling (1976) - Colonies which I observed in Texas, southeast of El Paso, and at the Jornada Experimental Range, New Mexico, were all nesting in very deep, soft sand. Tumuli were low, somewhat irregular craters, with an external diameter up to 20 cm. Cole (1954) reported this ant, as M. semirufa "Forel" (!) from White Sands National Monument, the nests with "... neat, circular, sand craters ... in open level sand areas with bunchgrasses and yucca between dunes." Although he reported that the gasters of living workers were a brilliant metallic blue color, I am unable to verify this phenomenon although I looked specifically for it in the material observed at the Jornada Experimental Range.

C. A. Kay and I attempted excavation of one colony at the Jornada Experimental Range, with largely unsatisfactory results. The nest was in deep, soft sand. While most honey ant species have a vertical, or nearly vertical, main shaft of considerable diameter descending to the nest, this species apparently does not. Rather, there are a few chambers near the surface. Descent to the nest proper is by way of a single, narrow tunnel which is very difficult to follow in the loose sand. At a depth in excess of four feet we abandoned the effort because, as the sand dried, the walls of the pit crumbled excessively. Since I found similar situations in sandy areas southeast of EI Paso, this may be a normal response of this species in soil of this type.

In New Mexico (Mackay and Mackay 2002) - Numerous habitats, ranging from grasslands through creosote bush scrub up to pinyon juniper woodlands. These ants have irregular craters, with a diameter up to 20 cms. This species can nest in loose, sandy soils, but prefers the more stable interdunal areas at White Sands National Monument. Cole (1954c) reports that the population at White Sands National Monument had brilliant blue gasters, that disappeared after the specimens were preserved. We have not seen this in any of this species that we have collected.

Castes

Minor Worker
Major Worker

Nomenclature

The following information is derived from Barry Bolton's New General Catalogue, a catalogue of the world's ants.

  • romainei. Myrmecocystus romainei Snelling, R.R., in Hunt & Snelling, 1975: 22 (w.) U.S.A. [First available use of Myrmecocystus melliger subsp. semirufus var. romainei Cole, 1936b: 120; unavailable name.] Snelling, R.R. 1976: 78 (q.m.).

Unless otherwise noted the text for the remainder of this section is reported from the publication that includes the original description.

This species has been confused with others by previous authors. The confusion began as early as 1908, for Wheeler's cotype series of mimicus includes romainei. I have not been able to reassemble the entire type series, said to consist of ". . . numerous workers, six males and six females ..." A pin of mimicus cotypes in the MCZ consisting of one female and two workers, and another pin of three worker cotypes in the LACM, are definitely romainei; other cotype pins, all workers, are mimicus as herein interpreted.

Cole described romainei as a variety of semirufa (i.e., kennedyi) from specimens collected 57 mi N of Cameron, Coconino Co., Ariz. The original description was not very detailed and was concerned primarily with differences between the new form and kennedyi. Creighton (1950) correctly recognized the similarities of this ant to mimicus and synonymized it with that name. Since the characteristics of mimicus were not at all clear at that time, the decision to do so is not surprising. It is my opinion, however, that this was incorrect and that romainei is an unusually distinctive species.

This medium-sized species is best recognized, in the worker and female, by the abundant erect hairs of the malar area and the uniformly short hairs on the occiput, promesonotum and gaster. The worker caste is further characterized by the rather closely micropunctate frons and vertex. The exceptionally short pleural hairs of the female are shared only with those of sympatric populations of mimicus. Since the malar area of the latter species is sparsely pilose, separation of the two is not difficult. When mimicus females possess more than two or three erect hairs on the malar area, these are still confined to the lower half of the area. In romainei they are evenly distributed along the entire area between the lower eye margin and the mandibular base. There are, furthermore, conspicuous erect hairs along the head margin behind the eye which project beyond the outer margin of the eye in full face view.

Workers of romainei from Utah and central Arizona are characterized by a weakening of the punctures of the vertex to the extent that it may be virtually impunctate at the sides. Such specimens closely resemble samples of flaviceps from the Mojave Desert and may not always be recognizable as romainei. Available material is too limited for adequate analysis, but these variant romainei possess some pronotal hairs which are more than 0.5 x MOD; inflaviceps the pronotal hairs are less than 0.5 x MOD.

The male, because it lacks conspicuous appressed pubescence on the first three terga, is readily separable from all species except kennedy and mimicus. The mesoscutal hairs of kennedyi males are half, or more, as long as the MOD; the frons, the center of the mesoscutum and the parapsis are polished and shiny. Males of allopatric mimicus populations also have long pleural hairs, but those of sympatric populations are more difficult to separate. The pleural hairs appear to average longer in such mimicus, about 0.12 mm, while in romainei they are shorter, about 0.08 mm.

The color of the head and thorax of romainei workers varies from light to medium ferruginous in the samples from Oklahoma, Texas, New Mexico, Arizona and Utah. The samples from Selden, Kansas, and Las Lunas, New Mexico, are unusually dark. These approach the brownish ferruginous color of mimicus from the same area but may be recognized by the closely micropunctate frons, densely pubescent frons, occiput, promesonotum and third tergum and more pilose malar area.

The Selden series consists of 21 workers from a single nest. In this series, 16 (76%) have a CI or 90 or more. In a similar series from the type locality and a single nest, selected as randomly as possible, 14 (67%) possess CI of 89 or less. The sample from Kenton, Oklahoma, consists of a dozen individuals of which lO (83%) have a CI in excess of 90. These samples are very limited, but it appears there may be a tendency toward relatively broader heads in northeastern samples.

Another variation involves large workers in samples from New Mexico and Texas. More specimens with HW at or above 1.23 mm have the petiolar scale broadened at the level of the spiracle, with the spiracle itself prominently projecting. When the petiole is viewed from above, the scale, excluding the spiracle, is about twice wider than long. This contrasts sharply with the usual shape, the scale 1.5 or less wider than long. This feature, apparently unique in Myrmecocystus, is not consistent; one worker, HW 1.23 mm, has a normal appearing petiole.

Smith (1935) recorded "melliger subsp. or var. from Oklahoma: Wichita Natl. Forest; Comanche Co.; Washita Co. I have been unable to locate any specimens from these localities but suspect they may prove to be romainei. They could, however, be mimicus and so these records must remain questionable for the present.

Description

Worker

Snelling 1976 figs. 136-145

Snelling (1976) - Measurements. HL 0.90-1.53 (1.17); HW 0.75-1.47 (1.03); SL 1.00-1.67 (1.37); WL 1.3-2.4 (1.7); PW 0.6-1.0 (0.7).

Head: Distinctly longer than broad to as broad as long, CI 80-100 (89), as long as to a little longer than scape, SI 100-121 (117). In frontal view, side straight in small workers, distinctly convex and abruptly convergent below in largest; occiput, in frontal view, with margin evenly convex (smallest workers) to flattened (largest), without lateral angle. Eye small, 1.00-1.25 x first flagellomere; OMD 1.45-2.00 (1.67) x EL. Mandible septemdentate.

Thorax: Moderately robust, PW 0.40-0.47 (0.42) x WL. Basal face of propodeum broadly rounded onto posterior face, distinctly shorter than posterior face.

Petiole: Usually about as thick as high, but in largest individuals may be higher than thick; crest rounded or flattened in frontal view, notched in largest workers; in dorsal view, about 1.4 x wider than long, in largest workers over twice wider than long and with distinctly projecting spiracles.

Vestiture: Pubescence sparse on clypeus, malar area and gula, conspicuously more abundant on frons and occiput; dense on thorax; dense and conspicuous on first three terga, sparse on following segments. Erect hairs abundant on head, with ten or more present on malar area; longest occipital hairs 0.5, or less, x MOD: pro notal hairs all shorter than EL, longest hairs on disc about one-third longer than shorter hairs and distinctly longer than those of hind tibia; mesonotum and propodeum with numerous fully erect hairs; petiolar scale with a few erect hairs; terga with abundant erect hairs, progressively a little longer on succeeding segments, those of first segment about as long as those of hind tibia. Appendages abundantly hairy; scape with erect hairs on all faces; femora and tibiae with erect hairs on all faces.

Integument: Clypeus polished, with scattered coarse punctures; frontal lobes, frons and occiput moderately shiny, lightly shagreened, frontal lobes finely and closely punctate, frons more coarsely and sparsely punctate and with abundant micropunctures; occiput more finely and sparsely punctate than frons; malar area moderately shiny and sparsely punctate, the punctures coarser and somewhat elongate near eyes, closely shagreened near mandibles and less shiny. Thorax slightly shiny and closely shagreened, without evident punctures. First three terga slightly shiny, densely shagreened, with scattered fine punctures and a few small poriform punctures.

Color: Head, alitrunk and appendages ferruginous, gaster blackish brown (see DISCUSSION).

Queen

Snelling (1976) - Measurements. HL 1.58-1.80; HW 1.67-1.88; SL 1.43-1.67; WL 3.8-4.3; PW 2.2-2.5.

Head: Sides straight, slightly convergent toward mandibular insertions; head as broad as, to broader than, long, CI 100-107; longer than scape, SI 88-94. Occiput, in frontal view, evenly convex from side to side, with broadly rounded lateral angles. Eye small, 1.09-1.20 x first flagellomere; OMD 1.54-1.75 x EL; OOD 3.3-5.5 x OD; IOD 2.0-3.3 x OD. Penultimate segment of maxillary palp slender, approximately parallel-sided. Mandible septemdentate.

Thorax: Moderately to very robust, PW 0.55-0.61 x WL. Scutum and scutellum moderately flattened. Basal face of propodeum ill-defined, broadly rounded into posterior face.

Petiole: Strongly compressed, crest angulate; in frontal view, crest deeply incised.

Vestiture: Pubescence diffuse on front of head and vertex, denser on occiput and malar area. Sparse on dorsum of thorax, longer and moderately dense on sides and on propodeum. Dense on first four terga.

Malar area with 15-20 erect hairs visible beyond margin in frontal view; longest occipital hairs about 0.5 x MOD. Longest mesoscutal hairs about equal to longest occipital; longest scutellar hairs subequal to MOD. Pleural hairs equal to shortest scutal hairs, very sparse, separated by their own length or more. Propodeal hairs about equal to longest scutal hairs. Petiole with abundant short, erect hairs on sides and crest. Terga with abundant erect, short hairs (those on disc of second segment about 0.1 mm), but those of apical segment about twice as long as on preceding segments; sparse and short on discs of ventral segments. Erect hairs abundant on all except posterior face of scape; abundant on extensor surface of femora; sparse on inner or fore femur; abundant on tibiae. Wing margins without fringe hairs.

Integument: Clypeus moderately shiny, lightly shagreened and with sparse coarse punctures; frontal lobes finely and densely punctate; frons and vertex moderately shiny, abundantly punctate, punctures finer and denser above; occiput closely micropunctate. Malar area slightly shiny, with abundant coarse, elongate punctures. Mesoscutum shiny, middle of disc impunctate, with sparse, fine punctures toward parapside; parapsis finely, closely punctate. Scutellum uniformly finely and closely punctate, punctures separated by a diameter or more. Pleura and propodeum slightly shiny, densely and finely punctate. First four terga moderately shiny, densely micropunctate and with scattered coarse piligerous punctures.

Color: Head, alitrunk and appendages ferruginous, gaster blackish brown. Wings whitish, veins and stigma yellowish.

Male

Snelling (1976) - Measurements. HL 0.80-0.93 (0.85); HW 0.77-0.90 (0.82); SL 0.80-0.93 (0.90); WL 1.8-2.2 (2.2); PW 1.1-1.2 (1.1).

Head: A little longer than broad to as long as broad, CI 95-100 (96), as long as, to shorter than, scape, SI 100-108 (106); in frontal view, sides straight and distinctly convergent toward mandibular insertions; occiput, in frontal view, evenly rounded, with broadly rounded lateral angle. OMD 0.78-0.89 (0.89) x EL; OOD 2.3-2.8 (2.3) x OD, IOD 2.3-3.3 (2.3) x OD. Mandible with a single tooth on apical margin or simple.

Thorax: Moderately robust, PW 0.49-0.64 (0.52) x WL. Propodeum with strongly sloping and poorly defined basal face.

Petiole: Moderately cuneate in profile, summit subangulate; in frontal view, crest broadly, shallowly concave.

Vestiture: Pubescence generally sparse, but moderately dense on occiput, pleura and propodeum.

Cephalic hairs sparse, short, longest occipital hairs less than 0.5 x MOD; malar area with 10-15 erect hairs. Mesoscutal hairs sparse, longest equal to about 0.5 x MOD; scutellar hairs longer, longest little shorter than MOD: pleural hairs sparse, shorter than 0.5 x MOD. Propodeum with a few short hairs laterobasally and on pleura. Petiolar scale with sparse, short hairs on sides and crest. Terga with scattered short hairs, longer on apical segment; sterna with hairs longer, sparse. Short, erect hairs abundant on scape and legs. Forewing without fringe hairs; hind wing with short, sparse fringe hairs on basal half of posterior margin.

Integument. Malar area dull, with close, fine punctures; rest of head slightly to moderately shiny, closely shagreened and with scattered fine punctures; discs of scutum and scutellum moderately shiny to shiny, lightly shagreened, more faintly in middle and with scattered fine, piligerous punctures. Pleura moderately shiny, moderately shagreened and with abundant fine punctures. Disc of propodeum smooth, impunctate and shiny, side moderately shiny, with abundant fine punctures. First three terga shiny, subpolished, very faintly shagreened; remaining terga and sterna less shiny, more distinctly shagreened.

Color: Blackish brown, mandibles, antennae and legs light brownish. Wings whitish, veins and stigma yellowish.


Type Material

Snelling (1976) - "Described from a series of 54 workers taken by Miss Marjorie Romaine, at Cameron, ARIZONA." Data labels on the specimens read: "57 mi. N Cameron, Ariz. 5/15/32 M. Romaine." Holotype and most paratypes in Los Angeles County Museum of Natural History; additional paratypes in American Museum of Natural History, Museum of Comparative Zoology, National Museum of Natural History.

References