Leptothorax foveata

The type worker, and an abnormal worker specimen were collected by Miss Mary Talbot in the nest of Aphaenogaster fulva subsp. aquia Buckley in a roadside ditch at Plainfield, Illinois [USA] on May 25, 1933. It is still only known from this type specimen.

Identification
This species is so different from all of the Leptothorax with which I am familiar that I am somewhat hesitant in trying to assign it to its proper taxonomical position. In Wheeler’s key to the species of Leptothorax (Proc. Acad. Nat. Sci. Phila. p. 223, (1903) the specimen would apparently key down to the acervorum canadensis group. From canadensis the species can be distinguished by the following characters: (1) lack of a distinct longitudinal impression on the clypeus, (2) longer scape, (3) shorter thorax, (4) poorly developed pro-mesonotal and meso-epinotal sutured, and (5) differently shaped petiole and postpetiole.

The most striking characteristics to me are the unusually prominent eyes of the worker, as well as the peculiar type of sculpturing; the species has, therefore, been very aptly named foveata.

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

Nomenclature

 *  foveatus. Leptothorax foveata Smith, M.R. 1934b: 211 (w.) U.S.A. Combination in L. (Myrafant): Smith, D.R. 1979: 1392. Currently subspecies of ambiguus: Creighton, 1950a: 263.

Taxonomic Notes
Creighton (1950): Dr. M. R. Smith now regards the insect which he described as the species foveatus in 1934 as very closely related to Temnothorax ambiguus if not actually a synonym of that species. In 1940 the Wessons recognized a variety of ambiguus to which they gave the name Temnothorax ambiguus pinetorum. The principal differences between foveatus and ambiguus are to be found in the more robust petiolar nodes and a slightly stronger impression of the sides of the thorax at the mesoepinotal suture in foveatus. According to the Wessons, the epinotal spines of pinetorum are notably longer than those of ambiguus and the thoracic rugae of pinetorum are feebler. In both cases the differences are clearly discernible only when the variants can be compared with the typical form. For this reason I have made no attempt to include either foveatus or pinetorum in the key. The problem of distinguishing between these variants and the typical ambiguus is by no means the only difficulty involved. We know practically nothing about the range of either insect. The two type specimens of foveatus were taken at Plainfield, Illinois. The type series of pinetorum and several other nests of this form came from Jackson County, Ohio. Since it has been customary to regard the range of the typical ambiguus as extending from eastern Canada and New England to the Dakotas, there is little present help to be secured from the occurrence of both foveatus and pinetorum at points approximately in the middle of this range. But it is by no means certain that the population which has previously been regarded as the typical ambiguus is a uniform one. It may be recalled that Emery utilized material coming from South Dakota, Ohio and New York as type specimens of ambiguus. In order to reduce confusion which might arise from a mixed type series, I propose to restrict the type series of ambiguus to those specimens which were taken in Hill City, South Dakota. There are two reasons why this is advantageous. Specimens from this same series, which are authentic and presumably cotypes, are present in three American museums. In the second place, if there is any tendency for ambiguus to produce geographical races, it may be safely assumed that the Hill City specimens represent the western race, for this station appears to be close to the western limit of the range of the species. Before anything certain can be stated as to the exact relationship of foveatus and pinetorum to the typical ambiguus it will be necessary to make a survey of the eastern population of ambiguus and determine to which of the three described forms this population belongs. Either foveatus or pinetorum may prove to be an eastern race of the typical ambiguus. I confess that it seems very unlikely that both will prove to be valid subspecies and perhaps both may prove to be inconsequential variations which lack any distributional significance. Until the matter can be definitely decided the two forms may be retained provisionally as subspecies.

Worker
Length 2.43mm.

Head moderately large, excluding the mandibles, noticeably longer than broad, with moderately convex sides, rounded posterior angles, and straight posterior border. Eyes large and prominent, oval, convex, placed near the middle of the sides of the head. Mandibles with 5 distinct teeth. Clypeus convex, with anterior border entire. Antenna 11-segmented; scape lacking its greatest width or slightly more of attaining the posterior border of the head; first funicular segment longer than segments 1 and 2 taken together. Thorax short, robust, convex above; viewed dorsally the humeri are rounded, the pro-mesonotal suture very faintly visible, and the meso-epinotal suture only slightly more perceptible. Epinotal spines moderately long and robust, directed upward, outward and backward. Petiole viewed in lateral profile with feebly concave anterior surface, faintly convex or flattened superior surface, which posteriorly rapidly descends toward the postpetiole. Postpetiole from above with convex node, which is very distinctly broader than long. Head, thorax, petiole, and postpetiole, with fovoeate impressions, subopaque; those on the head much finer, especially on the front and vertex where they are intermingled with very fine longitudinal rugulae; remainder of head, and dorsum of thorax, petiole, and postpetiole reticulate-foveate. Gaster glabrous, appendages, very similar.

Head, thorax, petiole, postpetiole, and gaster sparsely covered with short, erect, clavate hairs of a grayish or light yellowish color. Pubescence very fine and appressed, extremely sparse, most easily discernible on appendages.

Color deep reddish brown or ferruginous brown, with lighter appendages and gaster. Eyes and mandibular teeth black.