Crematogaster coarctata

Nevada, Wheeler and Wheeler (1986) - sixteen nests were under stones, 1 was exposed with a 50-mm crater, 1 was in duff at the base of a juniper, 2 were at the base of Sarcobatus vermiculatus, 3 were at the base of Atriplex confertifolia. Workers of C. coarctata were tending Phenacoccus solenopsis (Homoptera: Pseudococcidae; det. D.R. Miller) on the bases of stems of Atriplex confertifolia just below ground surface.

Identification
A member of the Crematogaster scutellaris group.

Morgan & Mackay (2017) - The key characteristics of Crematogaster coarctata are the intense striate-punctate sculpturing over the entire head and the pronotum being rounded with striae and with some punctures following the curvature of the pronotum. Crematogaster coarctata also has a highly variable anterior sternopetiolar process. The scape is also of variable length, always at least reaching the posterior border of the head.

The worker of this species is apparently identical to the worker of Crematogaster mutans and they are sympatric in distribution. There is a slight difference in the width of the mesosoma of the queens; the width of the mesosoma of C. coarctata, viewed from above, is wider than the width of its head and in C. mutans the width of the mesosoma is narrower than the width of its head. It is possible that C. mutans is a synonym, but more research on habits must be conducted and more specimens need be collected to be sure.

Crematogaster coarctata can easily be confused with Crematogaster cerasi and Crematogaster vermiculata. All three species have 1-5 long flexuous hairs on the pronotal shoulder with similar but not identical sculpturing. Pronotal shoulder sculpturing differs in that C. cerasi is more lineolate, C. vermiculata is vermiculate and C. coarctata is striate-shallowly punctate to areolate in sculpturing. The scape of C. coarctata always reaches the posterior border of head and often surpasses it; the scape of C. vermiculata is shorter but can reach the posterior border of head; the scape of C. cerasi extends about the first funicular segment past the corner. The head of C. coarctata is shiny medially to very and completely punctate in neat longitudinal rows, appearing as striolae, while C. vermiculata has a shiny head. The head of C. cerasi is mostly smooth and glossy, especially medially. The propodeal spines of C. coarctata and C. vermiculata are always long and straight while C. cerasi has reduced to medium length spines with the upper edge sinuous when viewed from the side.

It can be difficult to separate C. coarctata workers from those of Crematogaster dentinodis. The size, sculpture and color are nearly identical. The lack of development of spines or angles on the posterior lateral corners of the petiole usually works, but sometimes tiny angles are present in that position of workers of C. coarctata. It is important to collect a large series of different sized workers, and sometimes arbitrarily decide to which species specimens belong.

Crematogaster mormonum
This form can be separated from Crematogaster coarctata as follows: The workers can be recognized as the pronotum is nearly smooth and shining, the upper half of the mesopleuron has well defined rugae or striae, the lower half is punctate with the punctures lining up into striae, the side of the propodeum has striae with the background shining. The dorsum of the mesosoma has poorly defined striae with the background smooth and shining. The head and the posterior face of the propodeum are predominantly smooth and shining. The pronotum has several erect hairs (approximately 3) on each pronotal shoulder. (Mackay and Mackay 2002)

Crematogaster californica
It seems likely the synonymy of this taxon is incorrect and it should be treated as a valid species.

Distribution
Morgan & Mackay (2017) - Western United States from west Texas north to Montana; west to the Siskiyou Mountains of southwestern Oregon (Wittman et al., 2010), south to Baja California, Sonora, Chihuahua and Veracruz, México.

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

Biology
Morgan & Mackay (2017) - This common species is usually found in subterranean nests, sometimes with mounds and under stones or occupying downed logs. One nest was thatched (possibly an uninhabited Formica nest), others are craterlike in the soil surrounded by seed hulls, possibly abandoned Pogonomyrmex nests. They can also be found in cavities in plants and among exposed roots of plants. Brood were collected in nests in April, June, July and August, and sexuals were present in nests in March and July.

Workers forage in open areas on the soil surface diurnally and nocturnally and were collected in pitfall traps, and at Vienna sausage baits on the soil surface and in vegetation. Crematogaster coarctata have been observed tending Hemiargus isola and visiting extrafloral nectaries on cholla (Opuntia sp.) throughout the day, especially in arid habitats. This species has also been observed on saltbush, live oak, pine juniper and other desert shrubs. They collect seeds of the exotic shrub Cytisus scoparius in California and removed the eliaosome before discarding the remainder of the seed (Bossard, 1991). They are associated with gall inducing aphids (Valenti et al., 1996).

In northern California, they are only present in habitats when the Argentine ant (Linepithema humile) was absent (Human and Gordon, 1997). Various beetles are found in nests. It has been collected together with Genuchinus (Coleoptera: Scarabaeidae) beetles (Krikken, 1981) and with Genuchinus ineptus Horn (Cazier and Statham, 1962).

Crematogaster coarctata is found in a variety of habitats ranging from arid ecosystems to forested habitat. It has been collected in desert shrubland, thorn shrubland, shrubland in the Sonoran Desert of México, mesquite/grassland/creosotebush scrub, big sagebrush and in chaparral. It is common in chaparral vegetation in serpentine and non-serpentine soils (Fisher, 1997). It is the dominant ant in some forested habitats (Wittman et al., 2010, Wittman and Gotelli, 2011). It is found in burned and unburned fen and forest (Ratchford et al., 2005). Mackay and Mackay (unpublished) collected it in pinyon juniper forests with grama grass, oak/juniper grassland, oak woodland, riparian pine/oak forest, riparian Chihuahua pine forest, pines and junipers and in ponderosa pine/Douglas fir forests.

It occurs in several soil types including white sand, light brown, orange to dark brown rocky loam soils, light brown rocky sandy loam, to orange rocky soil.

Holway and Suarez (2006) determined the critical thermal maxima.

Nomenclature

 *  coarctata. Crematogaster coarctata Mayr, 1870b: 992 (w.) U.S.A.
 * Combination in C. (Acrocoelia): Emery, 1922e: 141.
 * Combination in C. (Crematogaster): Buren, 1968b: 94.
 * Junior synonym of lineolata: Mayr, 1886d: 462.
 * Revived from synonymy as subspecies of lineolata: Emery, 1895c: 283; Wheeler, W.M. 1904d: 270.
 * Revived status as species: Wheeler, W.M. 1919g: 111.
 * Subspecies of lineolata: Emery, 1922e: 141.
 * Subspecies of opaca: Enzmann, J. 1946c: 94.
 * Revived status as species: Creighton, 1950a: 207; Buren, 1968b: 94 (in key).
 * Senior synonym of californica, mormonum: Morgan & Mackay, 2017: 105.
 * californica. Crematogaster laeviuscula var. californica'' Wheeler, W.M. 1919g: 111 (w.) U.S.A.
 * [First available use of Crematogaster lineolata subsp. laeviuscula var. californica Emery, 1895c: 285; unavailable name.]
 * Combination in C. (Crematogaster): Buren, 1968b: 94.
 * Subspecies of lineolata: Wheeler, W.M. 1934f: 135.
 * Junior synonym of coarctata: Creighton, 1950a: 207.
 * Revived from synonymy and raised to species: Smith, M.R. 1951a: 808; Buren, 1968b: 94 (in key).
 * Junior synonym of coarctata: Morgan & Mackay, 2017: 105.
 * mormonum. Crematogaster coarctata var. mormonum Wheeler, W.M. 1919g: 111 (w.) U.S.A.
 * [First available use of Crematogaster lineolata subsp. coarctata var. mormonum Emery, 1895c: 284; unavailable name.]
 * Combination in C. (Acrocoelia): Emery, 1922e: 141.
 * Combination in C. (Crematogaster): Buren, 1968b: 94.
 * Raised to species: Creighton, 1950a: 215.
 * Junior synonym of coarctata: Morgan & Mackay, 2017: 105.

Taxonomic Notes
Morgan & Mackay (2017) - Emery (1895) described C. mormonum a variety of C. lineolata subspecies coarctata. In his list of Crematogaster, Wheeler (1919) raised C. coarctata to species and listed C. mormonum as a variety. Creighton (1950) stated that he had not seen intergrades between C. coarctata and C. mormonum and raised C. mormonum to species status. The differences between them have to do with longer scapes that surpass the head by at least the length of the first funicular segment in C. mormonum and less than the first segment in C. coarctata (Creighton, 1950, in key), or in difference in sculpturing of the head (Buren, 1968, in key) in which the head of the worker of C. coarctata is striato-punctate whereas the head of C. mormonum is smooth and shining behind the eyes or with only weak striation. There is so much variability in the first character, depending on the size of the worker (Creighton, 1950) and in the sculpturing of the head in many species of Crematogaster, even within some single series, to render both characters worthless. In comparing workers of type material of C. coarctata, to material labeled “possible type” and topotypes of C. mormonum from Salt Lake, Utah from the, we find no significant differences. Both taxa share the same sculpturing on the head consisting of deep striae below the eyes fading to shiny punctate medially; and longitudinally striate-shallowly punctate to areolate sculptured on the mesosoma. All have the scape at least reaching the posterior border of head to variable lengths past the border. The most interesting feature of these ants is the highly variable anterior sternopetiolar process. All have it and within a single nest series the variability can be from a slight nub to a well-developed and pointed process. Based on this evidence we consider C. mormonum to be a synonym of C. coarctata.

We have also compared workers of Crematogaster lineolata to the possible type of C. mormonum and observed differences in sculpturing and pilosity. The pronotal sculpturing and pilosity on C. lineolata is lineolate with many short bristle like hairs on the pronotum, C. mormonum differs in sculpturing with longitudinal rugae and 1-5 long flexuous erect hairs on the pronotum. They are clearly not the same taxon. Pilosity of the pronotal shoulder of C. coarctata is also variable, 1-5 long flexuous hairs, with 1-2 being the most common number.

Crematogaster lineolata subspecies laeviuscula var. californica was described by Emery in 1895. Creighton (1950) considered it to be a synonym of C. coarctata. Smith (1951) raised C. californica to species and Buren (1968) maintained this position in his key. We compared type workers of C. coarctata and C. californica, they appear to be essentially identical, and based on the lack of other evidence, and the arguments in Creighton (1950), we agree with Creighton that C. californica is a synonym of C. coarctata.