Temnothorax americanus

Temnothorax americanus is 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 (Temnothorax ambiguus, Temnothorax curvispinosus and Temnothorax longispinosus) 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.

Dulotic Temnothorax
Siefert et al. (2014) - Three slave-making species of the Temnothorax genus group (Bolton 2003) of the ant tribe Formicoxenini are known from North America. Each of the three represents an unmistakable combination of phenotypic characters. They all use species of the genus Temnothorax Forel, 1890 as hosts and cluster genetically with species of this genus (Beibl et al. 2005). The first species and outgroup to all the others (Beibl et al. 2005), Temnothorax americanus (Emery, 1895), is characterized by an elongated, semi-rectangular head capsule with extremely long antennal scobes that fully accommodate the short and flattened scape when it is folded back. These characters are a convergence to the Holarctic genus Harpagoxenus that belongs to the distantly related Leptothorax genus group. The second one, Temnothorax duloticus (Wesson, 1937), shows an acute, frontoventrally directed dent on the postpetiolar sternite, a high petiole with a bulky, truncate node that slopes down to the caudal cylinder with a distinct step. This particular petiolar shape and the reduction of antennal segments to 11 resemble the situation in the subgenus Mychothorax Ruzsky, 1904 of the genus Leptothorax Mayr, 1855. However, T. duloticus differs from the latter by the absence of a curved transverse carina on the stipes of the maxillae. On the third species….only little information exists to date (Herbers and Foitzik 2002, Beibl et al. 2005). Its phenotype is an unmistakable combination of an acute, frontoventrally directed dent on postpetiolar sternite, a stout, hump-backed mesosoma, small scape length, a high petiole that is in lateral aspect roughly triangular, a wide petiole and reduced mandibular dentition. Robin Stuart was the first who recognized the new species (Herbers and Foitzik 2002). We follow his proposal to name this slave-making species Temnothorax pilagens.

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.

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.

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.

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,