Key to Malagasy Carebara majors

This key to major workers is based on: [[Media:Azorsa, F., Fisher, B.L. 2018. Taxonomy of the ant genus Carebara in the Malagasy Region.pdf|Azorsa, F., Fisher, B.L. 2018. Taxonomy of the ant genus Carebara Westwood (Formicidae, Myrmicinae) in the Malagasy Region. ZooKeys. 767:1–149. (doi: 10.3897/zookeys.767.21105).]]

They included the following discussion about worker polymorphism, and it is quite useful to read this before you begin to use this key:

Most Carebara  species from the Malagasy Region show a remarkable range of morphological diversity, and this is especially noticeable in the major worker subcaste. In some cases, like Carebara jajoby, and Carebara nosindambo, there are four recognizable “intermediates” in the major worker subcaste (from the smallest, intermediate 1, to the largest, intermediate 4) in the same colony. Morphologically these intermediates are mosaics between major workers and queens.

The main variations present in the intermediates from the smallest to the largest are: a) posterolateral corners of head: moderately to strongly expanding posteriorly; b) posterior margin of head: weakly to strongly concave; c) size of the eyes: in some species from one to 75 ommatidia; d) number of ocelli: from one to three; e) form of the mesosoma: showing remnants of queen flight sclerites; f ) propodeal spiracle: distance of propodeal spiracle to declivity of propodeum closer to midlength of propodeal sclerite in larger intermediates; g) hair abundance; and h) sculpture: weakly to strongly sculptured.

All the variations present in the intermediates were included in the identification key, and can be separated using the major worker key. In some cases, larger intermediates are similar in the form of the head, but they differ in the form of the propodeum, petiole, as well as in the pilosity, so the user should check all characters mentioned on each part of the key.

There is also a key for minor workers: Key to Malagasy Carebara minors

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 * Carebara
 * Madagascar

1

 * Antennae 9-segmented . . . . . 2


 * Antennae 10- or 11-segmented . . . . . 3

2
return to couplet #1
 * Mandible with six teeth; dorsum of head and mesosoma smooth and shiny, genae and frontal lobes anteriorly with short longitudinal rugulae, not surpassing mid-length of head; head relatively long (HL 0.56–0.84) (Fig. 4A) . . . . . Carebara grandidieri


 * Mandible with five teeth, dorsum of head and mesosoma areolate-rugose, genae and frontal lobes with long longitudinal rugulae, surpassing mid-length of head, head relatively short (HL 0.45–0.53) (Fig. 4B) . . . . . Carebara creolei

3
return to couplet #1
 * Posterodorsal corner of propodeum angulate or convex, without a triangular tooth, or armed with at least a dentiform angle (Fig. 5A, B) . . . . . 4


 * Posterodorsal corner of propodeum with a triangular tooth (Fig. 5C, D) . . . . . 8

4
return to couplet #3
 * Dorsum of head with well-defined longitudinal rugae on the frons, extending to the posterior margin (Fig. 6A); head laterally with longitudinal rugae extending from mandibular insertion to posterolateral corner of head . . . . . Carebara placida


 * Dorsum of head with at least the frons smooth and shiny (Fig. 6B, C, D); head laterally with fine longitudinal rugulae extending from mandibular insertions to about eye level or slightly beyond . . . . . 5

5
return to couplet #4
 * In full-face view posterolateral corners of head narrowing posteriorly and their prominent appearance enhanced by the relatively deep median impression of the posterior margin (Fig. 6D) . . . . . Carebara malagasy


 * In full-face view posterolateral corners of head evenly rounded, not prominent, their short, broad appearance enhanced by the relatively shallow median impression of the posterior margin (Fig. 6B, C) . . . . . 6

6
return to couplet #5
 * In full-face view, mandible with six teeth; in profile, combined outline of dorsal surface of peduncle and anterior face of node medially concave; anterodorsal corner of node more broadly rounded, petiole node longer (PNL 0.12–0.15); petiole and postpetiole with all hairs suberect to subdecumbent (Fig. 7C); dorsum of propodeum with more than ten long erect to suberect hairs . . . . . Carebara hiragasy


 * In full-face view, mandible with five teeth; in profile, combined outline of dorsal surface of peduncle and anterior face of node nearly flat (Fig. 7A, B); anterodorsal corner of node convex or narrowly rounded, petiole node short (PNL 0.08–0.11); dorsum of propodeum with fewer than ten erect or suberect hairs . . . . . 7

7
return to couplet #6
 * In full-face view, dorsum of head with well defined longitudinal rugae laterally, and smooth and shiny middle area; in profile gaster with abundant long suberect hairs; distance from propodeal spiracle to declivity less or same as the diameter of the spiracle (Fig. 7A) . . . . . Carebara tanana


 * In full-face view, dorsum of head smooth and shiny or with fine longitudinal rugae laterally, smooth and shiny frons; in profile gaster with short decumbent to subdecumbent hairs and long subdecumbent to suberect hairs; distance from propodeal spiracle to declivity same or greater than the diameter of the spiracle (Fig. 7B) . . . . . Carebara bara

8
return to couplet #3
 * In full-face view, lateral margins of head straight or weakly convex, when weakly convex posterolateral corners nearly rounded (Fig. 8A, B, C, D) . . . . . 9


 * In full-face view, lateral margins of head convex or nearly straight, when nearly straight or weakly convex posterolateral corners of head more prominent and narrowing posteriorly (Fig. 8E, F, G H), when lateral margins are convex like (Fig. 8E) then posterolateral corners rounded . . . . . 16

9
return to couplet #8
 * Dorsal surface of head not completely sculptured, frons smooth and shiny, dorsolateral face of head with longitudinal rugae, mandible with five or six teeth (Fig. 9A, B) . . . . . 10


 * Dorsal surface of head sculptured, when median area of head not completely sculptured or smooth and shiny, head with longitudinal and irregular rugae and reticulate-rugose near the posterior margin, mandible with five teeth (Fig. 9C, D) . . . . . 13

10
return to couplet #9
 * In full-face view, head without transverse rugae near posterior margin of head, mandible with six teeth (Fig. 9A) . . . . . 11


 * In full-face view, head with transverse rugae near posterior margin of head, mandible with five teeth (Fig. 9B) . . . . . 12

11
return to couplet #10
 * In full-face view, head with longitudinal rugae, not extending to posterior margin of head, posterolateral lobes weakly sculptured, almost smooth and shiny; in profile, combined outline of dorsal surface of peduncle and anterior face of node nearly flat; posterior face of petiolar node nearly flat (Fig. 10A); distance from propodeal spiracle to declivity twice the diameter of the spiracle; posterolateral portion of cephalic dorsum lacking sculpture . . . . . Carebara omasi


 * In full-face view, head with longitudinal rugae, extending to posterior margin of head, posterolateral lobes sculptured; in profile, combined outline of dorsal surface of peduncle and anterior face of node medially concave; posterior face of petiolar node convex (Fig. 10B); distance from propodeal spiracle to declivity less than twice the diameter of the spiracle; posterolateral portion of cephalic dorsum sculptured . . . . . Carebara nosindambo

12
return to couplet #10
 * In profile, posterior face of petiolar node vertical to weakly concave; petiolar node short (PNL 0.07–0.11) (Fig. 11A); distance from propodeal spiracle to declivity equal to the diameter of the spiracle; declivity of propodeum flat . . . . . Carebara berivelo


 * In profile, posterior face of petiolar node steeply sloping and weakly convex; petiolar node long (PNL 0.11–0.12) (Fig. 11B); distance from propodeal spiracle to declivity less than the diameter of the spiracle; declivity of propodeum concave . . . . . Carebara tana

13
return to couplet #9
 * In profile, length of propodeal tooth less than the diameter of the propodeal spiracle; dorsum of propodeum slightly convex . . . . . 14


 * In profile, length of propodeal tooth equal to, or slightly greater than the diameter of the propodeal spiracle; dorsum of propodeum flat . . . . . 15

14
return to couplet #13
 * Dorsum of head with well-defined longitudinal rugae; irregular and transverse rugae present close to posterolateral corners and medially on posterior margin of head (Fig. 12A) . . . . . Carebara dota


 * Dorsum of head with fine longitudinal and irregular rugae laterally, rugae weakly defined on frons, rugoreticulum present close to posterior margin of head (Fig. 12 B) . . . . . Carebara demeter

15
return to couplet #13
 * In full-face view, posterolateral corners of head with a small triangular, tooth-like horn; dorsum of head longitudinally rugose laterally, becoming rugoreticulate medially, with a strong median longitudinal ruga reaching almost to the posterior margin of the head (Fig. 13A) . . . . . Carebara hainteny


 * In full-face view, posterolateral corners of head without teeth; dorsum of head with longitudinal rugae directed to posterolateral corners of head, without a distinctly stronger median ruga (Fig. 13B) . . . . . Carebara betsi

16
return to couplet #8
 * Lateral margins of head convex; occipital margin shallowly to moderately concave medially and posterolateral corners not prominent, rounded and not narrowed posteriorly (Fig. 14A, B) . . . . . 17


 * Lateral margins of head weakly convex, straight or nearly so medially; occipital margin deeply concave medially and posterolateral corners prominent, narrowed posteriorly (Fig. 14C, D) . . . . . 18

17
return to couplet #16
 * Posterodorsal corner of propodeum with a laminate triangular tooth that is slightly longer than the maximum propodeal spiracle diameter (PSL 0.08– 0.09); propodeal spiracle oval and separated by almost twice the diameter of the spiracle from the propodeal declivity (Fig. 15A) . . . . . Carebara mahafaly


 * Posterodorsal corner of propodeum with a triangular tooth that is shorter than the propodeal spiracle diameter (PSL 0.05); propodeal spiracle round and separated by less than half the diameter of the spiracle from the propodeal declivity (Fig. 15B) . . . . . Carebara salegi

18
return to couplet #16
 * In full face-view, dorsum of head smooth and shiny, or with fine longitudinal rugae laterally, extending from frontal lobes to midlenght of head, but never reaching to apices of frontal carinae and smooth and shiny frons (Fig. 16A, B, C) . . . . . 19


 * In full face-view, dorsum of head with well-defined longitudinal rugae, extending from frontal lobes to apices of frontal carinae, except for smooth and shiny frons (Fig. 18A, B, C) . . . . . 21

19
return to couplet #18
 * In profile, propodeal dorsum flat and slopes at about 30 degrees compared to the ventral margin of the metapleura, gaster with abundant short decumbent hairs; in dorsal view, anterior margin of pronotum sculptured, weakly areolate (Fig. 16E) . . . . . Carebara raberi


 * In profile, propodeal dorsum flat and slopes at about 45 degrees compared to the ventral margin of the metapleura; gaster with few short decumbent or appressed hairs; in dorsal view, anterior margin of pronotum smooth and shiny, in some cases weakly sculptured with short longitudinal rugae (Fig. 16D, F) . . . . . 20

20
return to couplet #19
 * In full face-view, posterolateral corners of head narrowed posteriorly (Fig. 16 A); propodeal tooth triangular and barely longer than propodeal spiracle, distance from posterior border of propodeal spiracle to declivity less than two times the diameter of the spiracle; combined outline of dorsal surface of peduncle and anterior face of node weakly concave (Fig. 17A) . . . . . Carebara sampi


 * In full-face view, posterolateral corners of head not as narrowed as above (Fig. 16C); propodeal tooth triangular and short, rarely longer than propodeal spiracle, distance from posterior border of propodeal spiracle to declivity same as or less than the diameter of the spiracle; combined outline of dorsal surface of peduncle and anterior face of node concave medially (Fig. 17B) . . . . . Carebara lova

21
return to couplet #18
 * In profile, propodeal tooh triangular, well defined, and longer than the diameter of the propodeal spiracle; narrow petiolar peduncle, anterodorsal face of petiolar node weakly convex or straight; in full-face view head usually heart shaped, posterolateral corners of head narrowed anteriorly, head weakly narrowed anteriorly (Fig. 18A, D) . . . . . Carebara jajoby


 * In profile, propodeal tooth triangular, and shorter or barely longer than the diameter of the propodeal spiracle; broad petiolar peduncle, anterodorsal face of petiolar node, convex or rounded; in full-face view head less heart shaped, posterolateral corners of head nearly rounded, head not narrowed anteriorly (Fig. 18B, C, E, F) . . . . . 22

22
return to couplet #21
 * In profile, petiolar peduncle tapering evenly from the node toward its anterior articulation, appearing slender anteriorly, dorsal margin of peduncle curving evenly into anterior margin of node, anterodorsal margin of petiole convex; propodeal lobes short and weakly convex, propodeal tooth shorter than propodeal spiracle diameter (Fig. 19A) . . . . . Carebara vazimba


 * In profile, petiolar peduncle not tapering, remaining deep almost to the anterior articulation and here narrowing abruptly, junction of dorsal margin of peduncle and anterior margin of node distinctly inflected, anterodorsal margin of petiole rounded; propodeal lobes short and weakly triangular, propodeal tooth slightly longer than propodeal spiracle diameter (Fig. 19B) . . . . . Carebara kabosy

worker caste diagnosis
The study that included this key also provided a "Morphological diagnosis of the worker caste of Carebara (adapted from, and with additions to Fischer et al. 2014)."

1 Workers polymorphic, dimorphic or monomorphic, allowing a division of the worker caste into smaller workers (minor worker) and larger workers (major worker). The major worker subcaste shows size differences, with intermediates between small and large major workers. Some species of the Old World with phragmotic heads in the major worker subcaste.

2 Eyes either absent or present (when present, small to medium sized, from 1–75 ommatidia). Major workers of some Malagasy species present one or more ommatidia in specimens from the same colony.

3 One to three ocelli occasionally developed in the major worker subcaste (intermediates). The number of ocelli is related to the size of the major worker.

4 Antennae with 8–11 segments, with a two-segmented club. In some Malagasy species (e.g. C. jajoby, C. nosindambo), the largest major worker (intermediate) may have one additional segment (11 segments) than medium, smaller major workers, and minor workers in the same nest series (10 segments).

5 Palpal formula 2,2 and 1,2.

6 Mandible subtriangular or triangular with four to seven teeth or denticles (three teeth in C. crigensis).

7 Clypeus with median area well defined, inserted between the frontal carinae, with rugae on the frontal carinae continuing to the anterior margin of the clypeus.

8 Clypeus of minor workers usually with four distinct setae (some species or specimens, e.g. C. carinata, C. sangi, C. lignata, with a central, isolated seta).

9 Frontal carinae covering the antennal sockets and often bases of the scapes.

10 Short antennal scrobe present on phragmotic major workers.

11 Head of major worker rarely bearing a pair of short, forwardly-directed horns or transverse ridges on the posterolateral lobes, or with posterolateral corners well developed.

12 Promesonotal suture usually distinct only laterally to the height of the spiracle, absent on dorsum, but usually present in larger major workers (intermediates).

13 Metanotal groove distinct and deeply or shallowly impressed on the dorsum.

14 Propodeum with posterodorsal corner rounded, sharply angulate or dentate, propodeal carinae lamellar.

15 Propodeal spiracle usually round.

16 Petiole peduncle relatively short or long, node distinct, subpetiolar process usually stoutly dentate.

17 Postpetiole with distinct node but lower than petiole in profile view.

18 Sculpture variable, smooth and shiny, punctate, striate, rugose, reticulate or costate.

19 Color yellow to deep brown.