Tetramorium caespitum species group

Diagnosis

Agavekar et al. (2017) - Twelve-segmented antennae; anterior clypeal margin complete and unspecialized; eyes of moderate size; antennal scapes of moderate length, not surpassing posterior head margin; antennal scrobes absent; frontal carinae very short to almost completely reduced; base of first gastral tergite not concave in dorsal view, without tubercles or teeth on each side; pilosity on dorsal surfaces of body erect to suberect with long and stout hairs; sting appendage dentiform.

Notes

Agavekar et al. (2017) - As noted by Bolton (1977), the Tetramorium caespitum group is the only endemic Tetramorium species group in the Palearctic, and it is widely distributed throughout all of Eurasia. Currently, it contains around 80 species and subspecies but this count has to be taken with a lot of caution and does not likely represent a realistic number. Compared to all other Tetramorium species groups, the Tetramorium caespitum group has never been comprehensively revised. Despite some recent small-scale revisionary treatments (Csosz, Radchenko & Schulz, 2007; Csosz & Schulz, 2010), its taxonomic situation can be classified as chaotic and no reliable identification resources exist for the group as a whole.

So far, only one species of the group is known from India: Tetramorium nursei. It occurs in Northwestern India representing the only genuine Palearctic component within the Indian Tetramorium fauna. It should be noted that the record of Tetramorium nursei from Kerala (Saranyan et al., 2013) is extremely dubious and very likely a misidentification. Species of the Tetramorium caespitum group are adapted to temperate and arid subtropical climate, thus not likely to occur in the Western Ghats.

Tetramorium ferox species complex

Based on Csösz and Schulz 2011.

Species

Identification

Key to Tetramorium ferox species complex workers

Diagnosis

Species belonging to the T. ferox-complex within the caespitum-group can be defined by the combination of the following characters.

Workers

petiole and postpetiole relatively broad (CS/PEW > 2.31, CS/PPW > 1.93), in T. aegeum and T. diomedeum very broad.
head, mesosoma and waist moderately sculptured; dorsum of both petiolar node and postpetiole medially shiny.
first gastral tergite smooth (excluding T. aegeum, for which 1st gastral tergite is imbricate); several long, erect hairs always appear on first gastral tergite.
propodeum in profile flat, sloping down at an angle of approximately 45°.
propodeal teeth small, developed as triangular denticles, in contrast to a prominent propodeal lobe.

Queens

mandibles smooth and shiny.
petiole and postpetiole wide.
mesosoma low, with flattened dorsum (seen in profile); scutum (seen from above) somewhat narrowed anteriorly and does not completely cover the pronotum, so that humeri (i. e. anterolateral pronotal angles) are easily visible.
head, mesosoma and waist moderately sculptured or smooth.
petiole and postpetiole with some very long thin hairs, in contrast to the first gastral tergite which is generally without long erect hairs.

Males

head and mesosoma moderately sculptured.
sides of petiole and postpetiole angulate in dorsal view.
stipes of genitalia curved inwards at the tip, and with flattened apical plate (seen in caudal view)

Tetramorium caespitum species complex

Based on Wagner et al. 2017.

Species

Identification

See Wagner et al. (2017) and https://webapp.uibk.ac.at/ecology/tetramorium/ for keys.

Diagnosis

Characters of species of the Tetramorium caespitum species 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.

(9) Male paramere length > 843 μm and thus larger than in Tetramorium semilaeve complex, T. ferox, Tetramorium moravicum, and T. pelagium.

(10) Large sexuals. Gyne MW > 1198 μm and thus larger than in Tetramorium semilaeve complex, T. brevicorne, Tetramorium punctatum Santschi, 1927, and T. pelagium.

Tetramorium chefketi species complex

Based on Csösz & Schulz 2007.

Species

Identification

Diagnosis

Workers

a) polygonal striae are continuous on 1st gastral tergite, and is sometimes microreticulate basally. Polygonal striation: interstices marked by feeble anastomosing striae (Fig. 8.), compare to microreticulation: interstices marked by very feeble elevated structures, like rugulae (Fig. 6, 7.);

b) head, alitrunk and waist coarsely sculptured, dorsum of petiolar node and postpetiole coarsely rugose and/or reticulate.

c) petiole and postpetiole relatively narrow (CS/PEW and CS/PPW, Table 1);

d) ground surface on the frons is usually coarsely microreticulate;

Gynes

e) alitrunk is low, dorsum is flattened in profile;

f) scutum in dorsal view is somewhat narrowed anteriorly and does not cover completely the pronotum, humeri are well visible;

g) head, alitrunk and waist are coarsely sculptured, and petiole and postpetiole dorsum coarsely rugose or/and reticulate;

h) polygonal striae disrupted on 1st first gastral tergite, sometimes microreticulate basally;

i) mandibles are longitudinally striate;

j) petiole and postpetiole are relatively narrow (WAIST, Table 2);

Males

k) head and alitrunk with usually coarsely sculpture, ground surface microreticulate;

l) sides of petiole and postpetiole not angulate as in the ferox species complex (in dorsal view);

m) first gastral tergite usually smooth and shiny, or feebly striate;

n) stipes of genitalia blunt, curved inwards at the top, with flattened apical plate (in caudal view)

notes

The newly defined chefketi species complex may not strictly reflect the phylogenetic relationship of the above-mentioned species. T. sulcinode and T. annectens possess several autapomorphic characters (e.g. relatively large eyes and a long psammophore) what probably may lead to place them into a separate group in a future.

Tetramorium semilaeve species complex

This problematic species-complex lacks a modern taxonomic revision.

Additional Resources

References