Tetramorium caespitum complex
As detailed in: Wagner, H.C., Arthofer, W., Seifert, B., Muster, C., Steiner, F.M. and Schlick-Steiner, B.C. 2017. Light at the end of the tunnel: Integrative taxonomy delimits cryptic species in the Tetramorium caespitum complex. Myrmecological News. 25:95-129.
This complex is one of four within the T. caespitum group. (T. semilaeve complex (Csősz and Schulz 2010), T. ferox complex (Csősz and Schulz 2010); T. chefketi complex (Güsten et al. 2006, Csősz et al. 2007), and the T. caespitum complex (Schlick-Steiner et al. 2006).
Characters of species of the Tetramorium caespitum complex are as follows:
(1) At least some workers of a nest with c-shaped,crinkly, or sinuous hairs arising just behind buccal cavity. Most typical character for Tetramorium caespitum complex; absent from Tetramorium semilaeve complex, Tetramorium ferox complex, Tetramorium chefketi complex, Tetramorium meridionale, Tetramorium brevicorne, Tetramorium hippocratis, and Tetramorium lucidulum, but also present in Tetramorium pelagium and Tetramorium goniommoide.
(2) Workers with microsculpture on basal part of 1st gastral tergite varying from few, scattered stickman-like to complex reticulate structures, MC1TG < 30 (error 0.0% in 993 workers). Very complex polygonal structure in Tetramorium chefketi complex, MC1TG > 40 (error 0.0% for 34 workers).
(3) Propodeal spines small to medium, PEW / SPST < 2.055 (error 0.0% for 471 nest means), 33.959 * POTCos - 8.569 * PPH + 7.487 * SPST + 649 < 0 (error 0.4% for 471 nest means). In European species of Tetramorium ferox complex and Tetramorium inerme, propodeal spines reduced to slightly developed corners, PEW / SPST > 2.055 ( > 2.08 in 11 workers). In T. brevicorne, propodeal spines rather long and number of postoculo-temporal costae and costulae high in relation to postpetiole height: 33.959 * POTCos - 8.569 * PPH + 7.487 * SPST + 649 > 0 (error 0.0% for 9 workers).
(4) Worker head, mesosoma, petiole, and postpetiole surface partly smooth (as in Tetramorium hungaricum) to coarsely sculptured (as in Tetramorium staerckei), but not largely smooth (as in T. inerme) or very coarsely sculptured as in T. chefketi complex and Tetramorium goniommoide.
(5) Worker head, dorsum, and occiput with longitudinal costae and costulae, but occiput never with transversal costae and costulae as in Tetramorium meridionale.
(6) Often dark brown to black. In Benelux, Central Europe, and Balkan mountain areas sometimes light brown (Tetramorium impurum); rarely reddish (Tetramorium immigrans); most species not yellowish (as in Tetramorium diomedeum, T. lucidulum, T. flavidulum) or reddish (as typical in T. ferox, Tetramorium punicum).
(7) Worker eye moderately sized, in nest mean EYE / CS = 0.155 - 0.196 (n = 471), but not > 0.197 as in Tetramorium pelagium and Tetramorium biskrense (n = 8 workers).
(8) Male with ten antennal segments, and not nine as in Tetramorium pelagium and Tetramorium biskrense.
(10) Large sexuals. Gyne MW > 1198 μm and thus larger than in Tetramorium semilaeve complex, T. brevicorne, Tetramorium punctatum Santschi, 1927, and T. pelagium.