Key to Tetramorium species groups of India

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This worker key is based on: Gaurav Agavekar, G., Hita Garcia, F., Economo, E.P. 2017. Taxonomic overview of the hyperdiverse ant genus Tetramorium Mayr (Hymenoptera, Formicidae) in India with descriptions and X-ray microtomography of two new species from the Andaman Islands. PeerJ 5:e3800 (DOI 10.7717/peerj.3800).

It is almost certain that future collecting in India will yield additional undescribed species. The key provided by Bharti & Kumar (2012) is a good foundation for the identification of most of the currently known Indian species. Here we provide a newly developed and illustrated species group key that allows a straightforward placement of species into their respective species group, and can be used to supplement the existing species level keys. This is especially useful when dealing with undescribed species.

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Figure 3. Differences in pilosity on body, gastral tergite, and antennal segments. Body in profile (A) T. rossi (CASTYPE12543), (B) T. obesum (CASENT0280874), (C) T. belgaense (CASENT0280882), (D) T. simillimum (CASENT0102390). First gastral tergite in profile (E) T. obesum (CASENT0280874), (F) T. walshi (CASENT0909098). Antennal funiculus, (G) T. smithi (CASENT0178421), (H) T. belgaense (CASENT0280882). Image (B, E, H) by Estella Ortega, image (F) by Zach Lieberman, image (G) by Erin Prado; all images from
Figure 4. Differences in head, petiole and sting appendage. Lateral head (antennal scrobe within ellipses) and petiole in profile view (A, B) T. smithi (CASENT0178421), (C) T. pilosum (CASENT0280881). Head in full-face view (clypeus within ellipses) (D) T. wroughtonii (CASENT0909204), (E) T. fergusoni (CASENT0909167). Sting appendage and head in full-face view (frontal carinae within ellipses) (F) T. smithi (CASENT0790832), (G) T. fergusoni (CASENT0901104, CASENT0909167), (H, I) T. mixtum (CASENT0790833, CASENT0280896). Image (A) by Erin Prado, image (I) by Estella Ortega; all images (except F and H) from
Figure 5. Differences in gaster, eye size, and frontal carinae. First gastral tergite in dorsal view (A) T. jarawa sp. n. (NCBS-AV761), (B) T. krishnani sp. n. (NCBS-AV940). Head in profile view (eyes under ellipses) (C) T. jarawa sp. n. (NCBS-AV761), (D) T. rugigaster (CASENT0901105). Head in full face view (frontal carinae in ellipses), (E) T. nursei (CASENT0901103), (F) T. krishnani sp. n. (NCBS-AV940). Images (D, E) by Ryan Perry; from
Figure 6. Differences in mesosoma and metatibiae pilosity and clypeus shape. Mesosoma profile view showing pilosity on dorsum of mesosoma. (A) T. simillimum (CASENT0102390), (B) T. tonganum (CASENT0103250). Head in full-face view (clypeus in ellipses), (C) T. bicarinatum (CASENT0125127), (D) T. barryi (CASENT0280889). Pilosity on metatibiae (E) T. flagellatum (CASENT0901097), (F) T. tonganum (CASENT0171074). Images by April Nobile, Michele Esposito, Ryan Perry, and Eli Sarnat; from
  • Species with distinctly branched (bifid, trifid, or very rarely quadrifid) hairs (Figs. 3A and 3B) . . . . . 2
  • Species without branched hairs, hairs present neither bifid, trifid, nor quadrifid, either with simple pilosity (Fig. 3C), or with reduced pilosity but short appressed pubescence (Fig. 3D) . . . . . 3


return to couplet #1

  • Pilosity on first gastral tergite predominantly erect with hairs simple, bifid, or a combination of both (Fig. 3E) . . . . . Tetramorium obesum group
  • Pilosity on first gastral tergite predominantly suberect with trifid or very rarely quadrifid hairs (Fig. 3F) . . . . . Tetramorium walshi group


return to couplet #1


return to couplet #3

  • Antennal scrobes present and well-developed with margin all-around (Fig. 4A); antennal scapes shorter (SI 65–75); petiolar node in profile high rectangular nodiform with moderately rounded anterodorsal and posterodorsal angles (Fig. 4B) . . . . . Tetramorium angulinode group
  • Character combination never as above, especially antennal scrobes, if present, always much less conspicuous than above, and without well-developed posterior and ventral margins (Fig. 4C) . . . . . Tetramorium tortuosum group


return to couplet #3

  • Head in full-face view distinctly cordate (Fig. 4D); lateral portion of clypeus modified into a low ridge in front of the antennal insertions (Fig. 4D); median cephalic and clypeal carinae/rugae absent (Fig. 4D) . . . . . Tetramorium melleum group
  • Head in full-face view never cordate as above (Fig. 4E); lateral portion of clypeus modified into a sharp and high ridge in front of the antennal insertions (Fig. 4E); median cephalic and clypeal carinae/rugae usually present, at least one of them (Fig. 4E) . . . . . 6


return to couplet #5

  • Sting appendage spatulate (Fig. 4F); frontal carinae very short, ending shortly behind level of posterior clypeal margin (Fig. 4G); antennal scrobes absent . . . . . Tetramorium fergusoni group
  • Sting appendage triangular to dentiform, but never spatulate (Fig. 4H); frontal carinae usually conspicuous and much longer than above, rarely short or absent (Fig. 4I); antennal scrobes present or absent . . . . . 7


return to couplet #6

  • Base of first gastral tergite with anterodorsal angles projecting as a pair of blunt teeth or horns (Fig. 5A) . . . . . 8
  • Base of first gastral tergite without anterodorsal angles projecting as a pair of blunt teeth or horns (Fig. 5B) . . . . . 9


return to couplet #7

  • Eyes moderately to strongly reduced, at most with five or six ommatidia in the longest row, usually just two or three. (Fig. 5C) . . . . . Tetramorium inglebyi group
  • Eyes moderately to well-developed and conspicuously much larger than above, at least with 10 or 11 ommatidia in the longest row (Fig. 5D) . . . . . Tetramorium mixtum group


return to couplet #7

  • Frontal carinae very short to almost completely reduced and antennal scrobes absent (Fig. 5E) . . . . . Tetramorium caespitum group
  • Frontal carinae variably developed, but never reduced or absent as above (Fig. 5F) . . . . . 10


return to couplet #9

  • Hairs on mesosomal dorsum equal to or shorter than maximum antennal scape width and stout apically (Fig. 6A) . . . . . Tetramorium simillimum group
  • Hairs on mesosomal dorsum usually significantly longer than maximum antennal scape width, if short then fine and acute apically (Fig. 6B) . . . . . 11


return to couplet #10

  • Anterior clypeal margin with distinct median impression, small in some species but always distinct (Fig. 6C) . . . . . Tetramorium bicarinatum group
  • Anterior clypeal margin complete, without median impression (Fig. 6D) . . . . . 12


return to couplet #11

  • Propodeal spines comparatively longer; metatibiae with conspicuous suberect to erect hairs on outer surface (Fig. 6E) . . . . . Tetramorium ciliatum group
  • Propodeal armament variable, ranging from almost absent to short teeth/spines, but always shorter than above; metatibiae with (usually) appressed to (rarely) decumbent hairs on outer surface (Fig. 6F) . . . . . Tetramorium tonganum group