Crematogaster opuntiae

These ants nest in cholla cactus, especially Opuntia fulgida. Nests are also found in the soil or under stones or in rotten wood, including under the bark of a standing, dead tree, and in limbs of oaks (Quercus sp.). Brood was found from March to October, sexuals in nests in July - September. The crickets Myrmecophila sp. occur in nests. (Mackay and Mackay 2002)

Identification
Buren (1968) - This species is very similar to Crematogaster californica, differing mainly in its shorter pubescence which is entirely appressed on head and scapes. The sculpturing, especially on the hind portions of the head, is weaker, and the colors are nearly always dark in life. C. californica is never associated with cactus so far as I have been able to determine. Since the two forms differ in both ecology and morphology, and their ranges seem to be separated by an impenetrable barrier, I have chosen to regard them as distinct species.

Mackay and Mackay (2002) - This species can be recognized by a single pair of hairs on the pronotal shoulder, and usually no other erect hairs on the dorsum of the mesosoma. The head is mostly shiny, the mesosoma coarsely punctate. The hemilobes of the postpetiole are blunt posteriorly. The pubescence on the head and scapes is mostly appressed.

Key to Crematogaster of the western United States

Distribution
Arizona, southern Nevada, southeastern California, south into northern Mexico.

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

Habitat
Mackay and Mackay (2002) - Chihuahuan Desert scrub and grasslands (especially grama grass), as well as transitional areas with the Sonoran Desert, up into pinyon-juniper forests, oak forests and ponderosa pine forests (up to 1380 meters elevation).

Biology
Buren (1968) - The species is very common within its rather circumscribed range within the Sonoran desert in Ariz., and surrounding semi-desert, but apparently reaches little into New Mexico, and to the south, in the Sonoran desert of Mexico, is replaced entirely in the cholla cactus areas by Crematogaster dentinodis. To the west, I have never been able to find the species beyond Ajo and Gila Bend, Ariz. Northward, insufficient sampling at present will not allow assessment of the limits of the range of opuntiae but I would expect it to occur only rarely beyond the limits of the Sonoran desert. This new species can be found most easily by searching for foraging workers on various cholla cactus species. Probably the chain fruit cholla, Opuntia fulgida, is the most frequented but there is no specificity to this plant.

Nevada, Wheeler and Wheeler (1986) - We have 4 records from 3 localities, all in the Hot Desert. We found 1 nest at the base of an Ephedra plant; our other 2 records were workers in the soil at the base of desert shrubs.

Nomenclature

 *  opuntiae. Crematogaster (Crematogaster) opuntiae Buren, 1968b: 120 (w.) U.S.A.

Worker
Length about 3.5 to 4.5 mm.

Head broader than long, with quite convex sides and rounded hind corners. Hind border nearly straight, slightly convex in small workers and slightly excised in large workers. Clypeal border gently convex. The head is usually noticeably narrower behind the eyes than in front, especially in medium sized and small specimens. Scapes evenly incrassated to tips, surpassing the hind corners of head by about one diameter even in large sized specimens. In smaller specimens the scapes may be a little longer, proportionately. Thorax flattened above in profile as is usual in this group of species, and with the mesonotal declivity short, poorly differentiated, or absent. Humeri not strongly developed, but nearly always distinct. Spines of moderate length, slender, sharp, and divergent. In some specimens, the spines may be outwardly curved at tip. Petiole of usual trapezoidal shape, the anterior corners moderately well developed and the anterior borders, as seen from above, usually not produced at right angles to the pedicel, but slightly to moderately oblique. Postpetiole with flattened hemilobes, the sides straight and subparallel or very slightly widening to the rear. Median sulcus of the postpetiole shallow in front, widening and deepening to the rear. In profile the hemilobes are somewhat produced posteriorly and are semiangulate behind. The petiole sometimes has a distinct anterio-ventral tooth developed on the front of the ventral keel.

Mandible, clypeus, and genae with the usual striae, those on the genae distinct only slightly past the eyes, sometimes fading out at about the middle of the eyes. Rest of head shining, and with only the very weak sculpturing of fine shagreening which becomes very faint puncturing on the vertex and occiput. Thorax strongly and densely punctate on nearly all its surfaces, even the declivity of epinotum faintly punctate in some specimens. There are also some distinct vermiculate rugae on the front of the pronotum and base of epinotum. Petiole and postpetiole very finely and densely punctate. Gaster finely shagreened, shining.

Erect hairs very few or nearly entirely absent on dorsum of head (excluding the usual anterior row of bristles on the clypeus.) On the thorax only a single erect hair on each pronotal shoulder. On petiole arid postpetiole, the usual posterior pairs of hairs only. On gaster, a very few scattered erect hairs and sparse rows of hairs at posterior borders of the tergites. Pubescence rather short and appressed or nearly so on all surfaces, including scapes and legs. The length of the pubescent hairs in relation to those of Crematogaster californica on the gaster can be assayed by noting that in opuntiae these fine hairs are usually not long enough to overlap those arising caudad.

Colors variable, especially in preserved material. The head and thorax may be reddish brown to black. Often the head is darker than the thorax. In life, foraging workers on cactus (Opuntia sp.) are usually quite dark and more nearly concolorous.

Type Material
I have chosen a worker collected in the Santa Rita Experimental Range, near Continental, Ariz. to be the holotype, and this locality becomes the type locality.

The species is known to me from the following localities and specimens from these have been marked as para types: Santa Rita Experimental Range, E. of Continental, Ariz., several series, W. F. Buren; on route 89 in New Mexico close to Arizona border, Buren; 10 mi. E. of Benson, Ariz., Buren; in Texas Canyon E. of Benson, Ariz., Buren; 50 mi. E. of Ajo, Ariz. on Ajo Road, Buren; Saguaro National Monument, E. of Tucson, Ariz., Buren; Sill, Ariz., Buren; 5 mi. S. of Oracle Junction, Ariz., Wm. S. Creighton; near Papago Reservation Boundary on Ajo Road, Ariz., Buren; Portal, Ariz., Creighton and Buren; 30 mi. N. of Tucson, Buren; 15 mi. E. of Globe, Ariz., Buren; Organ Pipe Nat. Mon., Buren; Abra Wash, Organ Pipe Nat. Mon., Creighton; Benson, Ariz., W. M. Wheeler; and Tucson, Ariz., W. M. Wheeler.