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Figures 28 - 31
Types. Holotype worker and paratypes (all castes): USA, Idaho National Engineering and Environmental Laboratory (INEEL), Bingham and Clark Counties, Idaho, U. S. A., 2 nest series, 31. viii. 1991 (# 9172, with males) and 22. ix. 1989 (# 8929, with alate queens) (W. H. Clark). Holotype worker and paratypes (all castes) in MCZC; paratypes also in ACIC, BMNH, CAFR, CASC, LACM, MNHG, and USNM. Topotypes in ACIC.
Etymology. From latin crassus = thick and ruga = wrinkle. The name is based on a feature of the mesosoma sculpture.
Worker. Habitus, figures 22, 25. Head in full face view, typically rounded, eyes centered on mid-line cutting the lateral margin, malar margin convex. Head slightly longer than broad (suboval) with convex sides, a convex or slightly straight (larger specimens) preoccipital margin, and very broadly rounded preoccipital corner. Median half of anterior margin of clypeus convex, border of lateral wings thick and sculptured so as to close the antennal fossae. Frontal lamellae rounded, reduced posterioly to short and narrowly subparallel carinae, merging to dorsum sculpture. Antennal scape rather long, surpassing the preoccipital corner by the length of the first two funiculus segments; sharply bent at base (almost right angle), with a reduced to moderately developed dorsal carina, either thin or lobate and surounding the shaft angle, shortly developing laterally and associated to a vertical thin and narrow ridge along basal shaft. In dorsal view shaft narrower along anterior half, about 1 / 3 the maximal width, particularly just after the bend; funicular segments 3 - 6 less than 1.5 times longer than broad; club 4 - segmented.
In profile, mesometasternum external margin horizontally aligned, mesosoma evenly convex, lower posteriorly; mesopropodeal suture not or very shallowly impressed; propodeal lobes angulate posterodorsally, but not pointed. Strigil of protibia with a basal tooth; middle and hind tibiae with large pectinate spurs. Propodeal spines of medium length, subparallel, surpassing slightly the propodeal lobes, usually straight and acuminate, sometimes slighly deflected, projecting backwards and upwards at just less than 45 °. Petiole higher than long and wide with a short but distinct peduncle; seen in profile the anterior face concave, forming a rounded right angle with the dorsal surface which is almost straight, while the posterior surface forms an arch. Postpetiole relatively short and low, very slightly larger than high in profile, node rounded, sternum subglobular.
Mandibles finely rugulose with ciliated punctures. Frons and clypeus longitudinally rugose; remainder of head dorsum with reticulated rugae, surface between rugae subopaque and punctulate. Antennal fossae with faint rugulae. Mesosoma strongly and deeply striated; rugae with flattened summit, longitudinally aligned, sometimes sinuous on pronotum. Petiole and pospetiole rugose. Gaster smooth and shining. General body color light to dark brownish-red; mesosoma often more reddish. Erect body hairs moderately abundant and long; gastric pubescence very dilute.
Queen. Habitus, figures 23, 26. Basically similar to workers in shape of head, characters of sculpture, color and pilosity of body except the following. Usual distinct mesosoma development of a queen and body size larger. Sculpture coarser on posterior half dorsum of head, on petiole and postpetiole, reduced on anteromedian third of pronotum, behind the collar. Surface between rugae of mesopleurae distinctly punctate; transverse groove narrow and deeply impressed; katepisternum with thinner rugae, largely separated, obliquely straight. Surface between spines subshining, faintly sculptured in upper third, then shagreened. Wings not tinted; submarginal cell partly divided. Gaster smooth and shining.
Male. Habitus, figures 24, 27. About the size of queen. In full face view head slightly longer than broad, narrower before eyes, without distinct antennal fossae, posterior half evenly rounded. Mandibles elongate, blade large and subtriangular; masticatory margin with three apical teeth followed by 2 - 3 teeth or denticles. Clypeus more or less bulging, anterior margin weakly convex. Malar space short. Frontal triangle depressed; lateral carinae paralled, weak, originating from toruli. Antennae with 13 segments; scapes rather thick and long, equal to first 3 - 4 funiculus segments; shaft with a short base, equal before the weak angle to 1 / 4 - 1 / 3 the scape length, flattened dorsally; funiculus with weakly enlarged club of 4 segments; second funicular segment longer than first, about twice the length of third. Eyes large and globular, with some erect, minute hairs. Ocelli small, 0.06 - 0.08 mm in diameter; distance between the posterior two equal to diameter of 4 anterior ocelli.
In lateral view, mesosoma rather long. Mayrian furrows not impressed, weakened or absent posteriorly. Spurs of meso and metalegs well pectinated. Metapleural lamellae small, not surpassing the petiole peduncle height. Wings as in queen. Propodeum without spines, just a more or less developed protuberences; spiracles rounded and well marked; surface with long, well separated, dark rugae. In profile petiole elongated with an anterior peduncle; ventral margin straight or very weakly concave; node with an anterior slope straight, summit rounded with horizontal rugulae. Postpetiole shorter, slightly larger than long; in profile higher than long; anterior and dorsal surfaces of dorsum forming a convex slope with apex posterior to center; sternum longer than high, ventral margin straight or convex.
Head sculpture generally fine; rugulae present on front, shorter and stronger around eyes and malar space, anastomosed on temples, surface punctulate. Mandibles subopaque, faintly sculptured. Clypeus very faintly sculptured, partly smooth, subshining mesially, often with a short median ruga from anterior margin. Frontal triangle punctulate. Front area with rugulae reaching the ocellar triangle, median part often only punctulate and shining; lateral carinae paralled, weak, originating from toruli. Temples punctate, with a varying abundance of short, partly anastomosed rugulae. Antennal scape with long suberect hairs over pubescence; funiculus with short, dense and erect pubescence, in addition a second layer of longer, erect dilute fine hairs. Pronotum and mesoscutum faintly sculptured, partly shagreened and smooth; mesoscutellum with longitudinal rugulae; mesoplurae shagreened or punctulate with few rugae or rugulae mostly associated to borders, transverse grooves strongly impressed, dark, base of some rugae origin. Propodeal protuberances with a row of fine erect hairs. Body pilosity moderately abundant, fine, erect to decumbent; denser and longer on head and legs. Postpetiole and gaster smooth and shining. Body color black to blackish brown; appendages lighter.
Specimens examined. All nest series available were recently collected (& # 8805; 1980). CANADA. British Columbia (CAFR). USA. Idaho (ALBRCIDA, CAFR, DEUI, LACM, UCDC), Montana (CAFR, USNM), Nevada (CAFR, LACM), Oregon (CAFR), Utah (CAFR, LACM), Washington (CAFR, LACM).
Notes. Rarely found in collections. Then either not identified or under the names M. americanaHNS, M. emeryanaHNS and M. lobifronsHNS. Based upon specimens deposited in CAFR, the species was reported from the INEEL by Allred and Cole (1971) as Myrmica lobicornisHNS.
The only literature concerning this species is Jackson et al. (1991) which was a chemotaxonomic study of the species based on specimens from INEEL. It showed that M. crassirugisHNS is distinctive from 14 described Nearctic MyrmicaHNS and that it shares some similarities with European species of MyrmicaHNS.
Range. A western species presently known from southern Canada down to southern USA. This ant should be found in Arizona, California, New Mexico, Wyoming and southern Alberta in addition to states and province mentioned hereafter.
Ecology. Collection records indicate this ant lives in semi-xerophilous prairie like sagebrush habitats and open rather dry coniferous forest of the upper Sonoran zone in mountains. Foragers have been collected on Atriplex confertifolia, Agropyron cristatum, Pterysia terebinthina, Balsamorhiza sagitta and Pinus sp. Collecting altitudes include 880 m in Oregon, 1465 - 2380 m in Idaho, 1870 m in Montana, 1935 - 2129 m in Utah, 1935 - 3134 m in Nevada. Nests are dug in mineral soils, uncovered or under rock and vegetation (herbs, shrubs). W. H. Clark and P Blom (personal communication) found M. crassirugisHNS in all of the major soil and vegetation types of the INEEL site, despite its very cryptic habits. A detailed account of the natural history of this ant will appear in a report on the ant fauna of that site to be published in Sociobiology.
Found most commonly in these habitats: 3 times found in shrub steppe, 4 times found in sagebrush, 1 times found in sagebrush desert, 1 times found in aspen grove.
Found most commonly in these microhabitats: 1 times on inflor. Ericameria nauseosa, 1 times at baits, 1 times nest in ground, 1 times nest under stone, 1 times ground nest, apparently at base of Artemisia arbuscula, 1 times ground forager(s), 1 times on low vegetation, 30 pm times nocturnal ground foragers, ca. 9, 1 times in dead base sagebrush.
Collected most commonly using these methods: 5 times search, 1 times baiting, 1 times attracted to shortbread cookie baits.
Elevations: collected from 260 - 2150 meters, 1232 meters average