Crematogaster minutissima

A diminutive ground-nesting species that also inhabits downed wood and acorns and nuts on the ground.

Identification
Longino (2003) - In Costa Rica Crematogaster minutissima is uniquely characterized by the combination of (1) yellow coloration; (2) humeral setae of mesosomal dorsum long, flexuous, and longer than any other mesosomal setae; (3) relatively short propodeal spines; and (4) relatively compact promesonotum. Similar Costa Rican species are Crematogaster wardi and Crematogaster flavomicrops.

Crematogaster minutissima and Crematogaster missouriensis (see also Creighton 1939) are small yellow ants with short, upturned propodeal spines, promesonotal setae in three ranks decreasing in length from front to back, dorsal face of petiole subquadrate, about as wide as long, scapes just reaching margin of vertex, and tibiae lacking the extremely long setae of Crematogaster sumichrasti and Crematogaster flavosensitiva. It occurs throughout the southern United States and south to northwestern Costa Rica. Within these parameters there is variation in overall size, degree of development of the anteroventral petiolar and postpetiolar teeth, strength of punctate sculpture on katepisternum and side of petiole, and queen size. This variability is the basis for the subspecies missouriensis from the central United States and the now synonymized smithi (= missouriensis) from the southwestern United States.

Crematogaster cubaensis and its synonym barbouri, restricted to Cuba, are similar to the population of small minutissima in Florida, but the promesonotum has a scruffy appearance, with abundant erect setae that are not clearly arranged in three ranks. Crematogaster wardi is a parapatric version of minutissima that occurs in wet forest habitats in Costa Rica. It has longer scapes, the promesonotum is longer and flatter, the three ranks of setae on the promesonotum are more nearly equal length, the propodeal spines are longer and directed posteriorly, and the dorsal face of the petiole is distinctly longer than wide.

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

Biology
Longino (2003) - The one Costa Rican record of this species is from Santa Rosa National Park in the seasonally dry northern Pacific lowlands. I collected a series of nocturnal foragers from low vegetation in the second growth forest around the administrative headquarters. In the USA the species is known to occur in a variety of habitats across the southern and central USA, nesting in dead wood on the ground. Where there is moist leaf litter they may be collected in Winkler samples of sifted leaf litter.

MacGown (2006) examined ants nesting or occupying hickory nuts in the Tombigbee National Forest (Ackerman Unit), Mississippi. While several hickory species were present, ants were found almost exclusively in the nuts of Carya glabra. Four colonies of Crematogaster minutissima were found, with 464 workers and 4 queens, 78 workers and 3 queens, 6 workers and 5 workers and 10 queens. This suggests that colonies contain less than a thousand workers, are likely monodomous (because most nuts contains queens) and polygonous (because multiple queens were always present in the nest). While C. minutissima colonies were found with relative ease and in large numbers in the hickory nuts by MacGown (2006), the species was otherwise only rarely encountered in the Tombigbee National Forest when using pitfall and other collecting methods.

Nomenclature

 *  minutissima. Crematogaster minutissima Mayr, 1870b: 995 (w.q.) U.S.A. Wheeler, W.M. 1908e: 484 (m.); Wheeler, G.C. & Wheeler, J. 1960b: 14 (l.). Combination in C. (Orthocrema): Emery, 1922e: 135. See also: Longino, 2003a: 84.

Worker
Longino (2003) - (Costa Rica) HL 0.538, 0.535, 0.577; HW 0.538, 0.542, 0.606; HC 0.497, 0.499, 0.539; SL 0.438, 0.430, 0.483; EL 0.149, 0.142, 0.165; A11L 0.219; A11W 0.103; A10L 0.085; A10W 0.078; A09L 0.047; A09W 0.058; A08L 0.040; A08W 0.053; WL 0.570, 0.547, 0.602; SPL 0.093, 0.081, 0.104; PTH 0.141, 0.130, 0.139; PTL 0.196, 0.198, 0.193; PTW 0.163, 0.162, 0.162; PPL 0.137, 0.134, 0.135; PPW 0.190, 0.173, 0.200; CI 100, 101, 105; OI 28, 27, 29; SI 81, 80, 84; PTHI 72, 66, 72; PTWI 83, 82, 84; PPI 139, 129, 148; SPI 16, 15, 17; ACI 1.15.

Color yellow orange; workers monomorphic in size.

Mandibles feebly striate on proximal half, smooth and shining with large piligerous puncta on distal half; clypeus with two longitudinal carinulae at anterior margin, anterior margin gently convex to straight; head slightly longer than wide, subquadrate, with flat posterior border; antenna with terminal two segments enlarged to form a club, third segment from end somewhat enlarged, blurring distinction between two and three-segmented club; scapes with abundant suberect flexuous setae; when scapes laid back from antennal insertions, they barely surpass margin of vertex; face smooth and shining, with a few concentric carinulae around antennal insertion; face covered with abundant, medium-length, suberect, moderately stiffened, amber setae, no appressed pubescence; in face view short setae project from lateral and posterior margins.

Promesonotum in lateral profile convex, forming an evenly curved arch; propodeal suture deep in dorsal view but partially obscured in profile by lateral carinulae that bridge the suture; propodeum with very short, weakly differentiated dorsal face and long posterior face; propodeal spines short, spiniform, upturned; pronotal dorsum with sparse longitudinal carinulae, interspaces smooth and shining; mesonotum with parallel lateral carinae that converge toward propodeal suture, continue across suture, and onto bases of propodeal spines; medial mesonotum concave, smooth and shining; posterior face of propodeum flat to concave, smooth and shining; side of pronotum smooth and shining; katepisternum and side of propodeum shining, largely smooth with traces of feeble carinulae; promesonotum with somewhat stiffened, amber, erect setae in three ranks, four across anterior pronotum (humeral pair 0.21mm, longer than medial pair), two at anterior mesonotum (0.l7mm), and two at mesonotal midlength (0.13mm); propodeal dorsum with two long setae, short inconspicuous setae sparsely scattered elsewhere on mesosomal dorsum, including on propodeal spines; tibiae with abundant short subdecumbent setae, none longer than maximum tibial width.

Petiole in side view trapezoidal, faintly microareolate, with longitudinal carinula at level of spiracle; anteroventral tooth small, rounded; dorsal face of petiole smooth and shining, subquadrate, longer than wide, with about six long amber setae along posterior border; postpetiole with small subacute anteroventral tooth, postpetiole in dorsal view subquadrate, wider than long, with emarginate posterior margin, abundant long setae; fourth abdominal tergite smooth and shining, with abundant long suberect somewhat stiffened amber setae, no appressed pubescence.

Queen
Longino (2003) - (Florida) A normal queen (dorsal face of propodeum drops steeply from postscutellum and much of propodeum appears ventral to scutellum and postscutellum) with general shape, sculpture, and pilosity characters of the worker; size characters as in Figures.

Type Material
Longino (2003) - Syntype worker, queen: “Aus Texas im Stockholmer Museum”, label on syntype worker “Texas” “Belfrage” “Stock” (examined).