Crematogaster larreae

A common species that nests in the roots of the creosotebush (Larrea tridentata).

Identification
Buren (1968) - The workers of larreae and Crematogaster depilis are surprisingly similar for species living in such close proximity. About the only character which will easily separate them is color, the head and thorax of depilis being reddish, while larreae is more concolorously very dark brown to black. Taxonomic distinction must fall on the structures of the females and males, especially the latter. The females of depilis have the entire pronotum punctate. The head is distinctly broader than long. The frontal furrow is strong and distinct to the first ocellus. The genae are striate to past the eyes; and the base of the epinotum has strong rugae or longitudinal striae. The color is usually a very dark concolorous reddish brown.

The males of the two species differ markedly. First there is a marked size range difference. All of the males of depilis measure 5.5 to 6.0 mm. The head is entirely punctate in depilis as is the pronotum. The spinal angles are often apparent in depilis and are always delimited by a tuft of long, flexuous pubescent hair. The coxae, femora, petiole, and postpetiole are also clothed with long erect pubescence. The pubescence is also erect and long on the venter of the head and suberect on hind corners of the head; the thorax has suberect to erect pubescence on nearly all surfaces. The vertex with its ocelli does not usually interrupt and distort the hind border of the head in full face view in depilis as it does in larreae.

Mackay and Mackay (2002) - Concolorous dark brown or black, and the mesosoma is densely and evenly punctate. The pranotal shoulders are without erect hairs, in fact there are rarely any erect hairs on the dorsum of the mesosoma. The head is finely sculptured with a mixture of punctures and striae, some parts, especially the central region, are nearly smooth and shining.

Key to western US Crematogaster

Distribution
California and east to west Texas, south into northern Mexico.

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



Habitat
Creosotebush scrub.

Biology
Buren (1968) - The determination of the identity of this cryptic species was of interest to me and may be related in part. I first became aware of the existence of this species in 1957 when, after summer rains, I took males and females of obviously two species of Crematogaster at lights several hours after sundown in the Coronado Hills residential area near the Franklin Mts. In El Paso. Searches within the next few days quickly established through captures of workers with associated winged forms that two very closely related species were-present on these slopes. Crematogaster depilis Wheeler was found in the lower trunks and roots of a number of desert plants, including Acacia sp., ocotillo, mesquite, and the creosote bush, but C. larreae was found only in creosote bushes. I had previously confounded the new species with depilis because of their extremely close resemblance in the worker form.

The captures of this species that I have made have all been associated with the creosote bush in widely ranging stations within the Chihuahuan, Sonoran, and Mohave deserts. Since this plant is perhaps the most common and characteristic bush plant of these and neighboring deserts, it might be postulated that larreae is equally wide ranging and common. This appears to be only partially true, for I have made searches for this ant in many localities in what appared to me to be favorable localities without success. In particular, I have been unable to find this ant at any station within the Colorado and Imperial deserts in spite of the commonness of the Cresote bush there. Although the factors responsible for this spotty distribution remain largely obscure, I do have at least a working hypothesis for the discontinuous distribution of this ant near El Paso, where I have made many collections (both positive and negative for larreae) and observations.

The cresote bush is very abundant near El Paso, occurring on the extensive, rocky, alluvial wash slopes of the Franklin mountains as well as in the surrounding sandy deserts. C. larreae in the creosote bush and C. depilis in various other desert trees and plants are common on the rocky slopes. In spite of many intensive searches, however, I have never been able to find either of these species in the immediately surrounding sandy deserts. In this case, no very subtile factors seem to be involved, but instead a possible case of elimination by intense competition. Night observation will quickly establish that Dorymyrmex bicolor, the predominant sandy desert dwelling species near El Paso, and several species of Myrmecocystus, in particular, Myrmecocystus mimicus and Myrmecocystus semirufus, are all quite active at night, leaving their nests in large numbers and foraging on the branches and leaves of the creosote bushes and other plants. Since C. larreae and depilis also forage mostly at night on these same species of plants, all these species would be in direct competition and possible conflict if exactly the same territories were occupied. Neither Dorymyrmex bicolor nor the two common Myrmecocystus'' spp. colonize in the mountain slopes, probably because of inability to construct their nests in the extremely hard and compacted rocky aluvium.

Mackay and Mackay (2002) - This ant nests in the roots of the creosotebush, Larrea tridentata, in galleries of wood boring beetles. A nest occupies a single bush, but may be in various roots of the same plant. There is a single queen and a mean of 789 adult ants in a nest. The larval population peaks in the fall and winter, pupae are found in the spring. Males are most commonly found in the nest in June, with flights occurring during the last 2 weeks of June and during July. Foragers are active 24 hours per day, with activity peaking in summer. They feed on nectar, honeydew and dead insects. They apparently cause no damage to the creosote, and may even form a mutualistic relationship with the shrub.

Nevada, Wheeler and Wheeler (1986) - We have 7 records from 6 localities in the southern part of the state; 2,800-5,800 ft. All are from the Hot Desert. Workers were found in the soil around the bases of desert plants (2 Larrea and 3 Ephedra).

Nomenclature

 *  larreae. Crematogaster (Crematogaster) larreae Buren, 1968b: 117 (w.q.m.) U.S.A.

Worker
Length 3 to 3.6 mm., an occasional specimen up to 4.0 mm.

Head a little broader than long, with convex sides, and hind border straight or slightly concave in the center. Clypeal border evenly and gently convex. Scapes shorter than head, surpassing hind corners only slightly in larger workers, terminal third of scapes incrassated. Thorax flattened above in profile, without or with only very weakly developed mesonotal declivity. Mesoepinotal impression shallow. Pronotal humeri apparent. Weak lateral oblique pro-mesonotal impressions present. Spines rather short, straight, and weakly divergent. Petiole trapezoidal, anterior corners moderately produced and convex. Postpetiole broader behind than in front, the hemilobes well separated by a broad median sulcus behind, but the sulcus may be very weak or almost absent in front in some specimens. In profile hemilobes produced posteriorly, weakly angulate there.

Dorsum of head shining, but with apparent shagreening which becomes weak puncturing on the occiput. Mandibles, clypeus, and genae with the usual striae, the genae more striato-punctate than is usual in most species and becoming punctate to the rear of the frontal carinae. Thorax entirely and fairly strongly punctate, subopaque; even the declivity of epinotum weakly punctate. Front of pronotum with weak vermiculate rugae. Base of epinotum with a few longitudinal striae. Sides and dorsa of petiole and postpetiole entirely punctate. Gaster with fine shagreening.

Dorsum of head, thorax, petiole, and gaster devoid of erect hairs. Only the postpetiole may sometimes have the usual posterior pair. Pubescence short and entirely appressed on all surfaces.

Head, thorax, and appendages always very dark brown as far as known. Gaster black.

Queen
Length about 8.5 to 10.0 mm.

Head subsquare, as broad as long or very slightly longer than broad. Eyes and ocelli large, the ocelli turned on their sides as in several closely related species. Frontal furrow weak to moderate. Scapes failing to reach hind corners of head by appreciable distance. Thorax slender. Spines short but sharp. Petiolar anterior angles well produced. Postpetiole trapezoidal, wider in front than behind.

Major portion of head smooth; genal striae not carried past the eyes (unlike depilis.) Rear fourth of pronotum smooth. Rear half or third of sides of mesosterum striato-punctate. Metapleura striato-punctate. Sides of epinotum striate or striato-punctate. Base of epinotum with weak irregular rugae. Sides of petiole striato-punctate. Hairs very sparse on dorsal surfaces, but present on head, thorax, and gaster. Venter of head with moderate number of erect flexuous hairs. Pubescence short and appressed on all surfaces.

Dark brown to black. Wing veins and stigma brown.

Type Material
The type locality of this new species is El Paso, Tex., where it may be found commonly nesting in the lower stems and roots of the desert plant, Larrea divaricata Cav., growing on the compacted rocky aluvial washes surrounding the bases of the Franklin Mts. I have found C. larreae in numerous specimens of this plant on a number of occasions at El Paso and have taken males and females at lights in El Paso. I have also captured the species at Van Horn, Tex., 10 mi. E. of Gila Bend, Ariz., and at Yucca Grove, Calif., all of these specimens from lower stems and roots of Larrea. I have chosen a male taken with workers at El Paso to be the holotype and all the other specimens, including the winged forms at lights, are marked as paratypes.

Holotype and several paratypes of each sex will be deposited in the National Musem, but I will retain most of the paratypes.