Temnothorax americanus

Temnothorax americanus (previously known as Protomognathus americanus) is a social parasite of a number of widespread and common Temnothorax species that occur in North America.

Identification
This ant is a Myrmicinae that is differentiated from other genera in the subfamily by the combination of mandibles with four teeth, a median concavity present on the anterior clypeal border and the presence of well-developed antennal scrobes. Most similar to Harpagoxenus but this other genus differs in having smooth mandibles with no teeth.

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

Biology
P. americanus is fairly well studied. This surely has something to do with its abundance. It can be common in local areas where a suitable host is present and abundant and the three species it parasitizes (, and ) are in fact quite common. Raiding occurs by workers invading a foreign nest, causing the natal workers to flee, and raiding individuals absconding with eggs, larvae and pupae. Pupae that are taken back to the Protomognathus americanus nest and allowed to eclose become workers within this colony.

Creighton (1929) found that dealate P. americanus queens were able to gain access to laboratory maintained nests of Temnothorax, establish themselves on the brood pile and over time eventually maim and kill all the resident workers. Existing queens were not attacked but did eventually die, presumably from starvation. Pupae that subsequently eclose form constitute the first workers that are not hostile to the P. americanus queen and attend to her needs.

Nomenclature

 *  americanus. Tomognathus americanus Emery, 1895c: 272 (w.) U.S.A. Creighton, 1927: 27 (q.m.); Wheeler, G.C. & Wheeler, J. 1955b: 26 (l.). Combination in T. (Protomognathus): Wheeler, W.M. 1905a: 3; in Harpagoxenus: Wheeler, W.M. 1910g: 494; in Protomognathus: Cover, in Hölldobler & Wilson, 1990: 65; in Temnothorax: Ward et al., 2014: 15. See also: Smith, M.R. 1939b: 166.

Type Material
Washington D. C., im Neste von Leptothorax curvispinosus (=Temnothorax curvispinosus) Mayr von Herrn Pergande gefunden. Ein Exemplar aus Beatty, Pennsylvanien, ohne weitere Angabe.

A syntype worker is located in the Emery collection,

Worker
Picea, pilosa et microscopice pubescens, capite thoraceque creberrime reticulato-punctatis, illius dimidio postico et fronte tamen laevioribus, nitidulis, clypeo laevi, nitido, medio depresso et late emarginato, mandibularum margine masticatorio dente apicali valido, aliisque 3-4 brevibus, obtusis armato, antennarum flagelli articulo]. tribus sequentibus aulo breviore, 2-6 transversis; thorace versus metanoti basin depresso, sutura tamen non impressa, spinis brevibus, rectis, divergentibus; abdominis nitidissimi pedunculo punctulato, segmento 1. antice breviter petiolato, postice cum nodo squamiformi, 2. Transverse ovato, praecedente fere duplo latiore, subtus mutico, scapis et pedibus sine pilis erectis. Long. 2 ½ - 2 ¾ mm.

Smith (1939) - Length 2.5-2.75 mm.

Head subrectangular, distinctly longer than broad, with very feebly emarginate or straight posterior border, rounded occipital angles, and moderately convex sides. Mandible rather small, convex, 3- to 4-toothed, apical tooth much larger than others. Anterior border of clypeus with a prominent and broad median emargination, which is distinctly broader than long; each side of emargination with an angular tooth or projection; posterior border of clypeus rounded, extending backward between frontal carinae. Frontal area not clearly defined. Frontal carinae prominent, longer than antennal scapes, and forming rather deep and distinct scrobes into which the scapes rest when in repose. Antenna 11-segmented; scape stout, curved, strongly depressed; last three segments of funiculus greatly enlarged, ultimate segment slightly exceeding combined length of the two preceding segments, funicular segments 2-6 each clearly broader than long. Thorax, from above, with rounded humeral angles; promesonotal suture present but not always very distinct, mesoepinotal constriction especially pronounced laterally; epinotal spines rather short, acute, directed upward, backward, and outward. Petiole, viewed laterally, scalelike, with abruptly sloping anterior and posterior faces, which meet to form a sharp superior border; viewed posteriorly, sides of petiole converging dorsally toward the superior border, which is narrow laterally, entire or feebly emarginate; ventral surface of peduncle with a prominent tooth anteriorly. Postpetiole, from above, considerably broader than long; viewed laterally, lacking a ventral tooth. Gaster strongly constricted at base, and with feeble basal angles.

Mandibles, clypeus, dorsal surface of head, anterior surface of petiole, and gaster rather smooth and shining; cheeks, and sides of thorax longitudinally rugulose-punctate; antennal scrobes, dorsum of thorax, and dorsal surfaces of petiole and postpetiole finely punctulate, the thorax often with fine rugulae.

Hairs long and erect, moderately abundant, present on all parts of body except appendages; a few hairs sometimes present on coxae, trochan ters, and bases of femora. Pubescence sparse, appressed, most easily discernible on appendages but also visible on other parts of body under certain lights.

Color varying from almost uniform deep brown to brownish black, with the mandibles, clypeus, antennae, coxae, trochanters, base of femora, and tarsi lighter; eyes, mandibular teeth, and edges of frontal carinae black.

Queen
Smith (1939) - Length 2.7-3.5 mm.

Excluding the usual morphological differences and size, so similar to worker as to be easily associated. Wings whitish, pilose, with ciliated margins; veins pale, indistinct. Anterior wing with a discoidal, a cubital, and an open radial cell, as well as a fairly large but pale stigma.

Male
Creighton (1927) - Length: 2.7 mm.

Color: head, thorax and abdomen brownish black; antennae and legs very pale, almost transparent in fresh specimens. Head rugulose with numerous erect hairs. Thorax feebly rugulose, somewhat glabrous, and with fewer hairs. Abdomen glabrous with sparse erect hairs. Antennae 12-jointed. Funiculus without a distinct club but the joints gradually increasing in diameter towards the tip. First funicular joint pyriform, much broader than those immediately succeeding it. Second and third funicular joints cylindrical and distinctly shorter than the adjacent joints. The following joints sub-oval and gradually increasing in length towards the tip. Scape one quarter the length of the funiculus. Scape and funiculus clothed with a short erect pubescence. Antennal scrobes much shallower than in female and worker, but distinct. Mandibles long and narrow, feebly toothed and sharply mueronate at the tip. Neck long and flattened dorso-ventrally.

Anterior face of mesonotum abruptly projecting above pronotum. Mayrian furrows strongly impressed at the promesonotal suture, bat becoming feeble at their point of confluence. Fore wings with a short open radial cell. Hind wings veinless except for faint impressions at the base of the wing. Epinotum unarmed. Second node of petiole without ventral tooth, squamiform, broader and less constricted behind than in worker.

Petiolar hairs sparse.

Smith (1939) - Length 2.7 mm.

Posterior border of head and occipital angles strongly rounded. Eye convex, protuberant, occupying approximately one-half-length of side of head. Distance between two lateral ocelli greater than that between either of them and median ocellus. Antennal scrobe extending from anterior end of frontal carina to above and somewhat behind eye. Antenna 12-segmented; scape approximately as long as first five funicular segments; first funicular segment pyriform. Clypeus strongly convex, its anterior border with a broad emargination. Mandible with a long, prominent, apical tooth, followed by a broad, blunt edge which is sometimes finely denticulate, sometimes toothless. Thorax with Mayrian furrows and parapsidal furrows; propleuron deeply concave laterally; epinotum without spines but often with a pair of blunt angulations. Wings like those of female. Petiole, viewed laterally, with a blunt superior border; ventrally with a longitudinal carina, which sometimes bears a small tooth anteriorly. Postpetiole distinctly broader than long; ventral surface without a tooth. Base of gaster scarcely wider than posterior border of postpetiole. Genital appendages not remarkably large; a pair of terminal cerci.

Head and thorax subopaque, with reticulate-punctulate shagreening; dorsum of thorax more finely sculptured and shining. Gaster smooth and shining, petiole and postpetiole almost smooth and glabrous.

Body with grayish, moderately long, sparse hairs, those on appendages shorter and suberect.

Color varying from deep brownish black to black; with mandibles, appendages, wings, apex of gaster, and genital appendages pale yellowish white; edges of mandibles brownish to black.