Temnothorax arboreus

An arboreal species, workers have been collected from the trunk and beaten from foliage of Pinus jeffreyi. That this ant is arboreal further distinguishes it from Temnothorax nitens, a species that nests in soil, often under small covering objects such as stones.

Identification
Snelling et al. (2014) - Promesonotum flat, followed by sloping dorsal face of the propodeum, so that in lateral view propodeal angles are relatively low on the declivity; head shiny, varying from weakly sculptured to smooth; petiole node robust and triangular in profile; propodeal spines reduced to small angles; body color dark brown.

This species is similar to Temnothorax nitens and in the key by Mackay (2000) it will run, with some difficulty, to Temnothorax melinus, a synonym of T. nitens. From T. nitens it differs in the much darker color, the obtuse propodeal denticles that are shorter than the subpetiolar tooth, and the considerably more robust petiole node.

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

Castes
Known only from the worker caste.

Nomenclature

 *  arboreus. Temnothorax arboreus Snelling, Borowiec & Prebus, 2014: 38, figs. 5, 19, 24–26 (w.) UNITED STATES.

Worker
Worker measurements (mm) (4 measured): EL 0.128–0.142 (0.136); HFL 0.201–0.444 (0.371); HFW 0.101–0.123 (0.112); HL 0.584–0.652 (0.614); HW 0.475–0.534 (0.502); IOD 0.416–0.453 (0.435); OMD 0.151–0.187 (0.168); PPW 0.197–0.217 (0.206); PSL 0.025–0.034 (0.030); PTW 0.136–0.151 (0.143); PW 0.328–0.369 (0.347); SL 0.395–0.447 (0.425); WL 0.647–0.761 (0.702). Indices: CI 79.6–85.6 (81.8); FI 83.1–84.4 (83.9); OI 21.6–23.0 (22.1); PI 142–145 (144); PSI 4.28–5.21 (4.88); SI 67.6–71.3 (69.2).

Head longer than broad in frontal view, lateral margins very weakly curved, posterior margin flat to weakly curved. Antennal scape ending below posterior margin by more than its apical width; apical club distinctly 3-segmented. IOD 3.04–3.33 × EL; EL 0.75–0.91 × OMD. Mandible finely longitudinally rugose. Clypeus with 1 or 2 short fine carinae on either side of median carina. Dorsum of head shiny, mostly smooth between scattered fine piligerous punctures; area around frontal carinae moderately shiny and weakly reticulate; malar area with several short fine longitudinal rugae, interspaces dull and sharply reticulate; posterolateral angles of head moderately shiny and weakly reticulate. Dorsum of head with sparse short, fine setae. Mesosoma slender, WL 1.97–2.11 times longer than PW; mesosomal dorsum nearly flat in profile before sloping down to obtuse propodeal denticles. Mesosomal dorsum moderately shiny and weakly reticulate but pronotum posteriorly with transverse smooth band; side of pronotum moderately shiny and irregularly rugulose, interspaces inconsistently reticulate; posterior face of propodeum dull and reticulate. Metafemur 3.54–3.97 times longer than wide in dorsal view. Entire length of dorsum with >20 flattened setae that are distinctly longer than those of frons.

Petiole without anterior peduncle; node robust and subtriangular, no higher than thick, summit subacute; subpetiolar tooth short and acute. Postpetiole profile low; in dorsal view node 1.42–1.45 times width of petiole node. Both segments moderately shiny and mostly finely reticulate. Each node with 4–6 setae similar to those of mesosoma.

Gaster in dorsal view 2.86–3.02 times wider than postpetiole; disc of first tergite smooth and shiny between sparse piligerous punctures; disc with sparse suberect flattened setae similar to those of mesosoma and scattered finer prostrate pubescence.

Head and body dark brown, gaster darker posteriorly.

Type Material
Holotype worker, U.S.A.: CALIFORNIA: San Diego Co.: Wooded Hill, 3 km SW Mount Laguna, 1800 m, 32.85° -116.43°, 26.v.2004 (P. S. Ward #15254), on low vegetation [beating on Pinus jeffreyi foliage], Pinus jeffreyi forest (CASENT0339243). Paratypes. Same data as holotype, 1 worker (CASENT0339243), 2 workers (CASENT0339244) UCDC.

Etymology
From Latin, arboreus - of trees, in reference to this being an arboreal species.

References based on Global Ant Biodiversity Informatics

 * Snelling R.R., M. L. Borowiec, and M. M. Prebus. 2014. Studies on California ants: a review of the genus Temnothorax (Hymenoptera, Formicidae). ZooKeys 372: 2789. doi: 10.3897/zookeys.372.6039