Crematogaster mutans

This species in the female has a very large head, and the least voluminous thorax and gaster of any North American species known to me. The habitus is thus much like a dulqtic species. As temporary social parasitic species are known in the genus Crematogaster, the discovery of another would not be too surprising. If this new species is a temporary parasite the host must be either Crematogaster californica or Crematogaster mormonum or both, to my knowledge the only other ground nesting species occurring with any commonness in the foot-hills and lower mountains of California and western Nevada. Unfortunately, mixed incipient colonies, if they exist, have not yet been found. (Buren 1968)

Identification
Buren (1968) - Both the thorax and gaster of this species are slender and non-voluminous. The thorax is compressed, and the gaster is also quite slender, scarcely broader than the head and scarcely longer than the thorax. Moreover the gaster appears depressed or flattened dorsoventrally. Most North American species have the gaster considerably wider than the head, longer than the thorax, and not or scarcely depressed.

The females of mutans can be easily separated from all other North American species by the very long, silky, yellowish, appressed pubescence, the compressed thorax, depressed gaster, and proportionately very large head. The workers are not likely to be confused with any species except californica with which differentiation is rather subtile and not readily apparent at first gance. Identification confidence may be attained by noting the somewhat more square-like head shape of mutans with the scarcely or not at all produced clypeus, the strong anterio-ventral tooth of the petiole, usually much stronger than in californica, the unique shape of the postpetiole, and the appressed condition of the long pubescence on all surfaces, including scapes and legs.

Key to western US Crematogaster

Distribution
Nevada and the mountainous regions of California.

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

Biology
Nevada, Wheeler and Wheeler (1986) - We have 8 records from 6 localities in the western part of the state; 5,800-7,400 ft. All records with adequate notes are from Pinyon-Juniper Biome and all nests were under stones. The workers from one colony were tending the scales Eriococcus sp. (Homoptera: Eriococcidae; det. D.R. Miller) at ground-surface level on an unhealthy plant (Eriogonum cf. fasciculatum polifolium) at Lida Summit (Esmeralda Co.).

Nomenclature

 *  mutans. Crematogaster (Crematogaster) mutans Buren, 1968b: 115 (w.q.) U.S.A.

Worker
Length about 3.5 to 4.0 mm., in some colonies up to 4.5 mm.

Clypeal border in front straight, only slightly convex, or in some cases slightly concave, little produced forward beyond the level of the anteriolateral corners of the head, giving a rather truncate appearance to the anterior border of the head. Head a little wider than long, sides only feebly convex, and hind border straight or slightly concave in large specimens, sometimes slightly convex in small specimens. Hind corners of head more angular in the larger workers than in most species. Scapes surpassing hind corners by less than one diameter in large workers, by little more than this even in smaller specimens. Thorax with the same shape and almost the same sculpture as in Crematogaster californica, the promesonotum somewhat flattened above, the mesonotal declivity indistinct, the spines only moderately divergent, straight, and of moderate length. Petiole trapezoidal, with anterior angles rounded but well produced. Postpetiole with shallow sulcus and with poorly developed hemilobes, the sides straight, and, unlike any other North American species known, narrower behind than in front. The petiole has a very large anterio-ventral tooth-like process, which arises at the front of the median ventral keel.

Mandibles, clypeus, and genae wth the usual coarse striae; those near the eyes carried past the level of the eyes. Front not especially shining but without obvious sculpture except very faint shagreening. This changes gradually to puncturation on the vertex and occiput. Thorax all distinctly punctate as in californica, even the declivity of the epinotum punctate in large specimens; front of pronotum and base of epinotum also with weak to strong vermiculate rugae, their strength not especially correlated with size. Large workers often have weak to moderate striae on the lower portions of the metapleura. This species also usually has the median carina of the mesonotum complete for the entire length of this sclerite, although there are many exceptions to this condition. Gaster subshining, with very weak and shallow puncturation.

Erect hairs long and flexuous but very sparse, a few hairs on the head, one on each shoulder of the pronotum or entirely absent from the thorax, the usual single posterior pair each on petiole and postpetiole, and a very few scattered hairs on the gaster. Pubescence very long and apparent, appressed or nearly so on all surfaces including scapes and legs; whitish in color rather than pale yellowish as in the female, however.

Head and thorax dark reddish brown to dark brown. Gaster very dark brown or black.

Queen
Length about 8 mm.

Head, excluding mandibles, broader than long and with slightly excised or straight posterior border, wider behind than in front. Head very convex above in profile. Scapes reaching hind corners of head. Ocelli rather large, oval in shape, but not as well developed as in Crematogaster californica or Crematogaster nocturna. Frontal furrow usually weak, occasionally apparent. Head much broader than the very slender thorax, in a ratio of up to about 1.75 to 1.0, but usually about 1.5 to 1, the greatest difference of any North American species measured. Mesoscutum much longer than broad. Scutellum wider than long. Mesoscutum in profile strongly and convexly produced in front and overhanging the pronotum. Pronotum in a few specimens with distinct longitudinal ridges on each side parallel with and near the dorsal border. Metanotum not produced. Epinotal spines longer than is usual in females, about twice as long as diameter of base. Petiole in some specimens with greatly produced anterior corners, so that the dorsal face can be over 3 times as broad as long, but in most specimens not this developed.

Mandibles striate, without smooth sulcus at base. Clypeus often with median shining streak, otherwise striate. Genal striae strong and dense, carried back past the ocelli. Rear of head finely and densely but weakly striate. Pronotum subshining, weakly striato-punctate. Mesosternal sides with strong striae and faint intercalated punctures: mesopleura mostly shining. Metapleura strongly striate below, finely striato-punctate above. Epinotal sides finely striato-punctate anterior to the spiracles, coarsely striate behind them. Base of epinotum irregularly rugose. Sides of petiole with coarse striae and fine puncturing. Postpetiole smooth above.

Pubescent hairs pigmented and extremely long and silky on all parts, giving a pale yellowish sheen to the surfaces in some lights; appressed on all parts. Erect hairs sparse but present on all regions, more numerous on the gaster, long and setae-like.

Head and thorax brown or reddish brown. Gaster dark brown.

Type Material
I know this new species from Morena Lake, Calif., found Aug. 3, 1957, under a rock, W. F. Buren; between Reno and Carson City Nev., under rocks, edge of desert, Aug. 9, 1957, Buren; south of Julian, Calif. On route 79, Sept. 14, 1959, under rock, Buren; Desert View Park, San Diego Co., Calif., Apr. 23, 1952, Wm. S. Creighton; and two females only from 3 mi. N. E. of Tehachapi, Calif., Aug. 11, 1935, G. D. Hanna. I have marked as the holotype a female from Morena Lake, Calif., the type locality. The other specimens have all been marked as paratypes. The holotype and a number of paratypes will be sent to the National Museum, and a number of paratypes will be sent to the Museum of Comparative Zoology and the California Academy of Sciences.