Key to Crematogaster kelleri group workers

This worker key is based on: Blaimer, B.B. & Fisher, B.L. 2013. How much variation can one ant species hold? Species delimitation in the Crematogaster kelleri-group in Madagascar. PLoS ONE 8(7): e68082 (doi:10.1371/journal.pone.0068082).

C. kelleri, C. madagascariensis, C. hafahafa, C. hazolava, C. tavaratra

The kelleri group is distinguished by the following: 1) In lateral view promesonotum forming a straight (or at most slightly rounded) plane; 2) posterior face of the mesonotum long and distinctly set off from dorsal face and abruptly and steeply sloping into metanotal groove; 3) propodeal spines always spiniform, very short to medium-sized (SPI 0.07–0.24) and situated high on propodeum.

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A more detailed treatment of the castes of this group:

C. kelleri worker caste
Very small to large size (HW 0.60–1.16, WL 0.65–1.16).

Masticatory margin of mandibles with four teeth (five teeth in some large specimens of C. kelleri). Head shape fairly quadrate, usually wider than long (CI 1.04–1.16); posterior margin of head in full face view laterally rounded or subangular, sometimes medially slightly depressed; occipital carinae present; antennal scapes usually easily surpassing head margin, sometimes merely reaching head margin; midline of eyes situated at or slightly above midline of head in full face view; eyes fairly large (OI 0.18–0.27) and moderately protruding.

Pronotum laterally subangular; promesonotal suture usually absent or indistinct; mesonotum usually with a distinct dorsal and posterior face, and laterally carinate, angulate or subangulate; mesonotum often with posterolateral angular tubercules or denticles, and in lateral view outline of promesonotum usually characteristic: pronotum and dorsal face of mesonotum form a straight or slightly rounded plane, while the posterior face of the mesonotum slopes abruptly and steeply into the metanotal groove; metanotal groove shallow; propodeal spines very short to mediumsized (SPI 0.07–0.27), spiniform; dorsal face of propodeum almost as long as posterior face; petiole in dorsal view oval or suboval, rarely moderately flared, subpetiolar process variable from absent to a reduced angular dent to a small, but distinct tooth; postpetiole bilobed, but depth of median impression variable; subpostpetiolar process absent.

Sculpture reduced overall; head shiny to aciculate; mesosoma dorsally shiny and aciculate; propleuron aciculate, meso- and metapleuron mostly reticulate, sometimes carinulate; dorsal face of propodeum aciculate, posterior face shiny; dorsal face of petiole shiny; helcium dorsally carinulate; postpetiole dorsally aciculate; lateral and ventral face of petiole and postpetiole feebly reticulate; face with 4–14 (more commonly 8–12) erect, long, flexuous setae, and abundant shorter, decumbent to subdecumbent pubescence; number of erect, long, flexuous setae on promesonotum highly variable, but usually present are at least four pronotal setae, and two lateral setae each on dorsal and posterior face of mesonotum; petiole with a pair of long, erect setae on dorsoposterior tubercules; postpetiole with at least one pair of long erect dorsoposterior setae, sometimes additional erect pilosity; abdominal tergites and sternites four to seven with long erect pilosity that is mostly abundant though highly variable, and abundant to very abundant appressed, decumbent or suberect pubescence throughout. Color pale to medium yellow, light to dark brown.

C. kelleri queen caste
Small to medium size (HW 1.15–1.45, WL 1.70–2.34); with worker characters, except as follows.

Masticatory margin of mandibles with five to six teeth; antennal scapes of variable length; eyes fairly large (OI 0.27–0.32) and protruding, situated at or below midline of head in full face view; head shape quadrate, wider than long (CI 1.05–1.20), widest just posterior to eyes; posterior margin of head straight.

Mesosoma fairly compact (MSNI 0.75–0.98, WL 1.70–2.34); mesoscutum in dorsal view varying from longer than wide to as wide as long; dorsal face of propodeum short, posterior face abruptly sloping; propodeal spines present or absent (SPI 0.00–0.10), spiniform or dentiform; petiole lacking dorsoposterior tubercules; postpetiole with worker characters, but median impression less pronounced.

Sculpture mostly shiny and aciculate except for metapleuron, and with anteriormost part of propodeum carinulate, and face between eyes and antennal insertions sometimes costulate; erect pilosity moderately abundant on head, dorsal side of mesosoma and on metasoma, but shorter than in workers; petiole with or without a pair of long, flexuous dorsoposterior setae, sometimes other erect setae present laterally; erect pilosity on postpetiole variable, usually with at least one pair of dorsoposterior setae. Color similar to respective workers, but metasoma often darker. Wings clear.

C. kelleri male caste
Very small to small (HW 0.47–0.65, WL 0.85–1.24). Masticatory margin of mandibles with two to three teeth; clypeus squarely protruding; eyes large (OI 0.40–0.68) and protruding, midline of eyes situated well below midline of head, approaching clypeal margin; antennae 12-segmented, scapes very short (SI 0.18–0.24); head wider than long (CI 1.17–1.35); in full face view ocellar triangle situated at or below posterior head margin and may be slightly elevated with respect to rest of face; occipital carinae very distinct.

Mesosoma compact (MSNI 0.84–1.39, WL 0.85–1.24); mesoscutum in dorsal view as wide as long; scutellum in dorsal view laterally compressed, often distinctly tapering from anterior to posterior end, dorsoposterior portion pointed or truncate; dorsal face of propodeum very short or absent; propodeal spines absent; petiole in dorsal view oval, carinae or denticles absent and all margins rounded, in lateral view petiole anteriorly greatly tapered; subpetiolar process absent; postpetiole with weak median impression, more pronounced posteriorly; wings clear.

Head sculpture shiny to rugulose; clypeus with several carinulae; mesoscutum rugulose, scutellum shiny to aciculate, propodeum longitudinally carinulate, petiole and postpetiole rugulose to shiny; erect pilosity on face variable; mesoscutum with regular or scattered short, erect pilosity; posterior part of scutellum with more abundant, longer pilosity; petiole and postpetiole with distinct long dorsoposterior setae, and abundant erect pilosity dorsally and laterally; abdominal segments four to seven with abundant short suberect pubescence, longer erect pilosity lacking. Color mostly as in worker and queen, sometimes paler.

1

 * Postpetiole clearly bisected by a complete, deep, longitudinal median impression (Figs 5, 6) . . . . . 2


 * Postpetiole with shallow median impression anteriorly, more pronounced posteriorly (Figs 7, 8) . . . . . Crematogaster kelleri

2
return to couplet #1
 * Propodeal spiracle mostly confluent with base of propodeal spines (Fig. 9); propodeal spines short (SPI 0.07–0.15) . . . . . 3


 * Propodeal spiracle situated below base of propodeal spines (Fig. 10); propodeal spines medium length (SPI 0.17–0.24); far northern Madagascar . . . . . Crematogaster tavaratra

3
return to couplet #2
 * Postpetiole evenly colored (as in Fig. 5, 7, 8), body color other than yellow . . . . . 4


 * Postpetiole with ‘‘median stripe’’: longitudinal impression lighter colored than lobes (as in Fig. 6), or body color yellow (in this case median stripe present, but hard to see) . . . . . Crematogaster hazolava

4
return to couplet #3
 * Very small species (HW 0.68–0.72, WL 0.73–0.74); posterior head margin rounded; color dirty yellow; known only from Montagne d’Ambre massif . . . . . Crematogaster hafahafa


 * Medium to large species (HW 0.86–1.11, WL 0.92–1.16); posterior head margin usually with subangular corners, color brown or dark brown . . . . . Crematogaster madagascariensis