Stenamma meridionale

A forest species that forms small colonies.

Identification
Stenamma meridionale workers can be distinguished by the following characters: Large size, 3.4-4 mm; large eyes, which have 8-10 ommatidia in their greatest diameter; pronounced mesoepinotal constriction, which is often as much as 0.15 mm in its greatest length and from 0.05 to almost 0.10 mm in depth; the posteriorly sloping base of the epinotum; the long, finger-like epinotal spines; and the anteroposteriorly compressed petiolar node, which when viewed from above and behind is subrectangular and has a straight or weakly emarginate superior border. (Smith 1957)

Distribution
Virginia, Missouri, and Illinois south to South Carolina and Arkansas. The most northern locality from which this species has been collected is Oakwood, Vermilion County, Illinois, which is slightly above the 40th degree of latitude. (Smith 1957)

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



Biology
From Smith 1957: The only collections of meridionale made directly from colonies were those of Mary Talbot in the Droste Woods in St. Charles County, Missouri. She described the woods as a small, mixed oak-hickory woods, with large red and white oaks predominating. There was a great variety of other trees such as linden, elm, sycamore, maple, and sassafras. The collections were made in a pawpaw thicket occupying a gentle slope from a ridge to a small stream in the center of the woods. The trees overhead allowed moving patches of sunlight but did not form the continuous deep shade of beech-maple woods. There were scattered shrubs of buck brush, elderberry, sumach, etc., with the herb layers consisting of spring blooming flowers such as spring beauty, mandrake, dentura, and red trillium. The ground cover had a fairly heavy leaf covering mixed with a litter of twigs, acorns, hickory nuts and decaying branches. The soil was very dark and loose for three or four inches, then it became progressively compact and light colored until below six or seven inches it was a very hard-packed clay. Colony 48-2 was collected-November 10, 1948, from two chambers in which the ants were hibernating" in hard clay in depths of 10 and 15 inches. This colony was found when the air temperature was 43° F "and the soil temperature 52° F. In the 10 inch chamber both workers and larvae were found, in the 15-inch chamber only a few workers. Although the ground was dug to a depth of 21 inches, no other immature stages or adults were found. The total content of the nest was 19 workers and 36 medium to large larvae, but no pupae, females, "or males. This may not have represented the entire colony. The second colony, 52-12, was found October 6, 1952, in a chamber 13 inches deep which looked like a horizontal crack in the dry, hard clay. There had been no cold weather and the ants were still foraging in the woods. The air temperature at this time was 73° F, and the soil temperature 58° F. From the chamber were taken 11 workers and one dealate female, four have but no eggs, pupae, winged females or males.

In localities in other states where collections were usually made with Berlese funnel, single collections usually produced only from 1-13 workers with occasionally a dealate female. These individuals were largely taken from leaf mould, ground cover or top soil, mostly, if not entirely, in the woods. At this time- we do not know the maximum size of colonies, the diversity of the nesting habits nor the month or months of the year in which males and winged females are produced.

Talbot (1957) added some additional information to that she supplied to Smith. This information was part of a study where she excavated soil during the cooler months of the year, in a Missouri woodland, on order to survey ant nests. "Stenamma meridionale was found only once on the plots and once previously. The two colonies overwintered larvae, as did the other Stenamma. One occupied a chamber thirteen inches deep, and one had two chambers, ten and fifteen inches deep, in the hard, yellow clay. The colonies collected were small, being made up of sixteen and 55 individuals of which eleven and nineteen were workers."

Nomenclature

 *  meridionale. Stenamma meridionale Smith, M.R. 1957b: 169, pl. 4, fig. 15 (w.q.) U.S.A.

Worker
Length 4 mm. Last funicular segment 0.35 mm in length, longer than the combined lengths of the two preceding segments. Eye oblong, placed a little more than its greatest diameter from the base of the mandible, the greatest diameter less than 0.2 mm and composed of 9 or 10 ommatidia. Thorax 1.4 mm in length measured from the anterior border of the pronotal collar to the apices of the epinotal spines; with rather rounded or sub• angular humeri; widest through the prothorax (0.6 mm), narrowest through the epinotum (0.45 mm). In profile, with a very pronounced mesoepinotal impression which is approximately 0.15 mm in its greatest length and slightly more than 0.05 mm at its greatest depth. Base of epinotum distinctly inclined posteriorly, approximately 0.3 mm in length, the base of the epinotum meeting the declivity to form a pair of well developed, long, finger-like spines which are between 0.05-0.10 mm in length, and are directed posterodorsally and somewhat laterally. From above and somewhat behind, the petiolar node appears compressed anteroposteriorly and has subparallel sides and a weakly emarginate but not sharp, transverse, superior border. Postpetiole, from above, subcampanulate, scarcely longer than broad. Gaster, from above, oblong or subelliptical, without basal humeri.

Head with rather coarse, distinct sculpturing; front of head bearing a number of longitudinal striae which extend to approximately the posterior border of the head; much of the remainder of the head with rugulose-reticulate to reticulate sculpturing, the interspaces punctulate. Thorax, from above, with rather coarse and somewhat widely spaced rugulose-reticulate sculpturing, some of the rugulae on the pronotum, at least, with a longitudinal trend; side of thorax somewhat similarly sculptured except that perhaps the ventral half or more of the mesopleuron is largely reticulate. Pedicel and anterior face of petiolar node punctulate, the dorsal and posterior surface of the node rugulose-punctate; postpetiole sculptured somewhat similarly. Basigastric striae more than 0.1 mm in length. Frontal area, epinotal declivity and gaster smooth and shining. Most of the head, the thorax, petiole and postpetiole subopaque (slightly shining however in some lights).

Hairs moderately abundant, yellowish, of variable length, largely reclinate to suberect; apparently longest on the c1ypeus and the front of the head.

Body dark brown, to some extent with a blackish cast; anterior portion of the head, antennae, legs and apex of gaster a much lighter or yellowish brown.

Paratype workers vary from the holotype worker in the following characters: Body length 3.4-4 mm; head 1.10-1.12 times as long as broad with the posterior border straight or broadly and almost imperceptibly emarginate; length of thorax 1.25-1.4 mm; greatest width (through pronotum) 0.5-0.6 mm; narrowest width (through epinotum) 0.375-0.45 mm; last funicular segment 0.3-0.35 mm in length and longer than the combined lengths of the two preceding segments; the 1st, and 7th through 11th funicular segments, longer than broad; eye with 8-10 ommatidia in its greatest diameter; mandible usually with five basal teeth but occasionally as many as six teeth; superior border of petiole straight or feebly emarginate; postpetiole, from above, almost as broad as long to 1.2 times as long as broad; head, thorax, petiole and post. petiole from light brown to dark brown with a decided blackish cast.

Workers other than paratypes show the following variations: Body length 2.8-4 mm; head 1.10-1.23 times as long as broad; thoracic length 1-1.4 mm; greatest prothoracic breadth 0.45-0.60 mm; narrowest breadth of thorax (through epinotum) 0.35-0.40 mm; mesoepinotal impression 0.1-0.15 mm in length and usually about 0.05 mm in depth; last funicular segment 0.3-0.35 mm in length; greatest diameter of eye 0.1-0.15 mm with 6-10 ommatidia; petiolar node from above and behind with subparallel to dorsally converging sides and with the superior border of the node straight or rounded; sculpturing of head not always coarse; epinotal spines from tuberculiform to slender, digitiform; epinotum occasionally with a transverse welt at the base; pronotum and mesonotum often with well defined and rather broadly spaced longitudinal rugulae, the interspaces of which are either smooth or finely punctulate; body varying from light reddish brown to' dark reddish brown, the anterior portion of the head, appendages and apex of the gaster usually lighter.

Queen
Length 4.6 mm. Similar to the worker except in the following respects: Head 1.08 times as long as broad; anterior ocellus located approximately 0.4 mm back of frontal area; length of thorax 1.7 mm; greatest breadth of thorax (through the mesonotum anterior to the wing insertions) 0.85 mm; narrower breadth (through the epinotum) 0.55 mm; greatest diameter of eye between 0.25-0.30 mm with approximately 18 ommatidia; epinotal spines well developed, approximately 0.10 mm in length, stout, with blunt apices, from above, at least three times as far apart at the apices as are the length of the spines; mesonotum with well spaced, longitudinal rugulae; base of epinotum with coarse, transverse rugulae; sides of prothorax and epinotum largely with coarse, longitudinal rugulae with punctate interspaces, most of the mesopleuron largely smooth and shining.

Females other than the paratype show the following variations: Body length 3.9-4.6 mm; head 1.08-1.14 times as long as broad; anterior ocellus located from 0.35-0.40 mm back of frontal area; length of thorax 1.35-1.7 mm; greatest breadth of thorax 0.7-0.85 mm; narrowest breadth of thorax 0.40-0.55 mm; greatest diameter of eye 0.2-0.3 mm; with 14 to 18 ommatidia therein; epinotal spines 0.25-0.35 mm apart at their apices; mesopleuron usually more smooth and shining than the remainder of. the side of the thorax, although it may be sculptured somewhat; dorsal surface of body often infuscated, with the anterior portion of the head, the appendages and apex of gaster, and some scattered areas on the mesonotum lighter.

Type Material
Described from individuals collected from two colonies by Mary Talbot. The holotype and 15 paratype workers from colony No. 48-2 collected 11-10-48 and a wingless female and 11 paratype workers from colony No. 52-12 collected 10-6-52. All of these have been placed in the U. S. National Museum under U.S.N.M. No. 62392.

Type Locality Information
Droste Woods, St. Charles County, Missouri.

Etymology
Descriptive. Presumably Smith felt this species was relatively restricted in its latitudinal range, meridional L. = southern