Crematogaster rossi

Little is known about the biology of .

Identification
Buren (1968) - This species seems most closely related to Crematogaster californica Emery but is easily distinguishable from that species in either worker or female, the worker by its coarsely reticulate or vermiculate rugose thorax and more shining head, and the female by longer scapes, smaller ocelli, broader thorax and very broad scutellum, and several details of sculpture. Many workers also have the erect hairs somewhat more numerous than in californica. It is unlikely to be confused with any other species except, perhaps, Crematogaster vermiculata, with which, however, it has no real affinity. The type locality of vermiculata is recorded as Los Angeles, Calif. This is certainly in error but will undoubtedly cloud the identity of vermiculata for all time. I have examined types of vermiculata in the National Museum and they are, without shadow of a reasonable doubt, conspecific with the rather common small arboreal species which is restricted to cypress swamps throughout the southeastern states. Since the ecological habitat for this speces is restrictive, I see no possibility that vermiculata could have ever been captured in California and must consider the type series mislabeled. The ant which Dr. Creighton (1950) treated as vermiculata is californica.

Distribution based on type material
Mexico.

Nomenclature

 * . Crematogaster (Crematogaster) rossi Buren, 1968b: 111 (w.q.) MEXICO (Baja California, Nayarit).
 * Type-material: holotype worker, 22 paratype workers, 4 paratype queens.
 * Type-locality: holotype Mexico: Baja California, San Jose del Cabo (no collector’s name); paratypes: 19 workers, 4 queens with same data, 3 workers Mexico: Nayarit, Tepic (no collector’s name).
 * Type-depository: USNM.
 * Junior synonym of vermiculata: Morgan & Mackay, 2017: 396.
 * Status as species: Kempf, 1972a: 82; Bolton, 1995b: 161; Ward & Blaimer, 2022: 926.
 * Distribution: Mexico.

Worker
Length about 3.5 to 4.3 mm.

Head, excluding mandibles, a little broader than long, subrectangular in appearance, the sides more straight sided than in many species; posterior border slightly excised. Scapes surpassing posterior corners by about one diameter. Humeri of pronotum evident. Pro-mesonotal dorsum flattened in profile. Mesonotal declivity short or scarcely developed. Mesonotal carina moderate to weak, present in front only. Spines slender, divergent, sharp, of moderate length but less than the interbasal distance, straight or somewhat curved outwardly. Petiole broader than long, sometimes very broad, usually with rather angulate corners and straight sides, trapezoidal. Hemilobes of postpetiole not rounded, produced to the rear and semi-angulate there, median sulcus not strong, spiracular angles weakly produced.

Genal striae carried a little past the eyes. Front and most of rear of head shining or subshining; venter of head smooth and shining; vertex and middle of occiput weakly punctate or shagreened, a short median carinula often present on occiput. Pronotal front and dorsum strongly vermiculate or reticulate rugose. Mesonotal dorsum punctate and with irregular rugae or striae. Pronotal sides punctate with some striae in front. Mesopleura densely punctate. Metapleura densely punctate and rugose. Base of epinotum with irregular longitudinal rugae and fine dense punctures. Declivity of epinotum shining, faintly punctate. Petiole and post petiole punctate; postpetiole with tendency to have striae.

Pubescent hairs of moderate length, appressed on head, thorax, and gaster; on scapes subappressed to nearly erect. Erect hairs rather long and slender, sparse, on thorax only one or two on each shoulder; on gaster sometimes rather numerous and evenly scattered over first segment, in others less numerous, but always with the usual row near the posterior border of each segment. Postpetiole usually with accessory pairs of hairs. Head and thorax yellowish or light brownish red, the head usually a little darker than the thorax.

Queen
Length about 9 to 10 mm.

Head, excluding mandibles, broader than long, subsquare in appearance. Scapes reaching posterior corners or sometimes slightly surpassing them. Basal funicular joints about as broad as long. Ocelli large, smaller, however, than in Crematogaster californica, round to oval in shape. Eyes also large. Head slightly broader than thorax. Mesoscutum a little longer than broad. Scutellum very broad, sometimes well over one and one-half times as broad as long. Thorax more robust than in californica. Metanotum not produced into a point. Spines short, about equal to diameter of their bases. Postpetiole with quite strong spiracular angles. Gaster voluminous.

Mandibles striate, without smooth sulcus at base. Clypeus striate but with median shining streak. Genal striae coarse, carried past the eyes. Front, vertex, and occiput of head shining, nearly smooth. Hind corners of head usually with some fine but distinct striae. Pronotum finely punctate and with some irregular striae, these becoming distinct and longitudinal on lower posterior quarter, shining a little at extreme rear. Mesosternal sides striato-punctate on rear half, the striae stronger and denser than in californica; mesopleura smooth and shining. Metapleura strongly striate. Sides of epinotum strongly striate. Base of epinotum irregularly and transversely rugose. Petiole with strong striae and fine punctures on sides. Postpetiole striate above.

Pubescent hairs rather short and subappressed on all parts. A few, scattered erect hairs also present on all parts. Both erect hairs and appressed or subappressed pubescence present on venter of head.

Probably always concolorously dark brown in life but many specimens available to me now faded to a reddish brown. Wing veins and stigma dark brown.

Type Material
San Jose del Cabo, Baja California, Mexico.

I have before me the holotype worker and nineteen paratype workers and four paratype females from San Jose del Cabo, Baja California, and three paratype workers from Tepic, State of Nayarit, Mexico. Most of these will be returned to the U. S. National Museum but a few will be retained in my collecton. I also have seen a series of females from Triunfo, Baja California, and a single worker from Triunfo, Michelbacker and Ross, collectors.

Etymology
This species is named in honor of Dr. E. S. Ross of the California Academy of Natural Sciences.