Crematogaster sewellii

Crematogaster sewellii is commonly found in high-altitude grassland, savannah and woodland habitat in the central and south-central highland region (800-1500 m), and at lower elevations (160-600 m) in the Makay massif and the RF Beanka in western Madagascar. The species often co-occurs with Crematogaster mafybe and Crematogaster degeeri, and otherwise with all other species of the C. degeeri-assemblage except Crematogaster malahelo. This species appears to nest exclusively on the ground, either in the soil or under stones. (Blaimer and Fisher 2013)

Identification
Blaimer and Fisher (2013) - A member of the Crematogaster castanea group and Crematogaster degeeri assemblage.Crematogaster sewellii can be identified with the following unique combination of characters: very large eyes (OI 0.24-0.29), antennal scapes usually long (SI 0.77-0.87) and surpassing head margin, propodeal spines reduced to small denticles, and distinct bicoloration with head and thorax yellowish to dark orange and metasoma with abdominal segments four to seven black.

Distribution based on Regional Taxon Lists
Afrotropical Region: Comoros.

Worker
Additional images of workers can be found here

Nomenclature

 *  sewellii. Crematogaster inermis r. sewellii Forel, 1891b: 196, pl. 6, fig. 9 (w.) MADAGASCAR. Combination in C. (Crematogaster): Wheeler, W.M. 1922a: 844; in C. (Acrocoelia): Emery, 1922e: 148; in C. (Crematogaster): Bolton, 1995b: 166. Raised to species: Dalla Torre, 1893: 86; Mayr, 1895: 138; Emery, 1895f: 342. Current subspecies: nominal plus acis, marnoi.

Description
Blaimer and Fisher (2013):

Worker
(n = 20) HW 0.72-0.99; HL 0.66-0.89; EL 0.18-0.23; SL 0.56-0.70; WL 0.75-1.01; SPL 0.01-0.04; PTH 0.15-0.21; PTL 0.20-0.28; PTW 0.24-0.33; PPL 0.12-0.19; PPW 0.22-0.29; LHT 0.54-0.73; CI 1.08- 1.13; OI 0.24-0.29; SI 0.77-0.87; SPI 0. 01-0.05; PTHI 0.68-0.87; PTWI 1.07-1.32; PPI 1.54-1.92; LBI 1.30-1.45.

Masticatory margin of mandibles with four teeth; head shape fairly quadrate or slightly wider than long (CI 1.08-1.13); posterior margin of head in full-face view laterally subangular or rounded, often slightly medially depressed; occipital carinae distinct; antennal scapes usually reaching or surpassing head margin; midline of eyes situated distinctly above midline of head in full-face view; eyes large (OI 0.24-0.29) and strongly protruding. Pronotum laterally angular; promesonotal suture indistinct; mesonotum usually forming a flat plane with respect to pronotum; mesonotum usually with a short posterior face; mesonotum angular laterally, posterior face carinate, distinctly set off from propodeum; posterior face of mesonotum sloping steeply into metanotal groove; metanotal groove fairly shallow, laterally constricted and bordered by carinae; propodeal spines reduced to small denticles (SPI 0.01-0.05); dorsal face of propodeum short, but distinct; posterior face of propodeum gently sloping; petiole in dorsal view broadly oval, dorsolaterally rounded, without posterolateral tubercules or denticles; subpetiolar process variable; postpetiole bilobed with a broad median impression; subpostpetiolar process absent. Head sculpture aciculate; mesosoma, petiole, helcium and postpetiole reticulate; face usually with six to eight erect longer setae, and regular shorter, appressed pubescence; erect pilosity on promesonotum abundant, usually > ten setae; otherwise promesonotum dorsally with regular appressed to subdecumbent pubescence; propodeum laterally with two to four erect setae; petiole and postpetiole usually with a pair of long, erect setae posterolaterally, and shorter appressed pubescence; abdominal tergites and sternites four to seven with abundant short erect pilosity, and regular appressed to decumbent pubescence throughout. More or less bicolored: head, mesosoma, petiole and postpetiole reddish-orange to yellow, rest of metasoma black.

Queen
(n = 1) HW 1.25; HL 1.18; EL 0.40; SL 0.80; MSNW 1.13; MSNL 1.08; WL 1.97; SPL 0.00; PTH 0.33; PTL 0.42; PTW 0.47; PPL 0.30; PPW 0.47; LHT 0.93; CI 1.06; OI 0.34; SI 0.68; MSNI 1.04; SPI 0.00; PTHI 0.79; PTWI 1.14; PPI 1.59; LBI 2.12.

Small size (HW 1.25, WL 1.97). With worker characters, except as follows. Masticatory margin of mandibles with five teeth; antennal scapes surpassing level of lateral ocelli; eyes large (OI 0.34), situated at midline of head in full-face view; head shape square (CI 1.06); posterior margin straight. Mesoscutum in dorsal view as wide as long (MSNI 1.04); dorsal face of propodeum long and set off at right angle to posterior face; propodeal spines or tubercules absent; petiole moderately flared, postpetiole merely impressed behind; subpetiolar process variable. Sculpture aciculate throughout; face with eight longer erect setae (n = 1!) and abundant shorter erect to suberect pilosity; mesonotum with abundant short and scattered longer erect setae; petiole and postpetiole with dense short suberect pilosity, and postpetiole with additional longer dorso-posterior setae; abdominal tergites and sternites four to seven with abundant erect pilosity and appressed pubescence. Color as in workers; wings clear.

Male
(n = 1) HW 0.57; HL 0.46; EL 0.22; SL 0.11; MSNW 0.69; MSNL 0.61; WL 1.24; SPL 0.00; PTH 0.17; PTL 0.22; PTW 0.22; PPL 0.14; PPW 0.24; LHT 0.60; CI 1.23; OI 0.47; SI 0.24; MSNI 1.14; SPI 0.00; PTHI 0.77; PTWI 0.99; PPI 1.64; LBI 2.07.

Small (HW 0.57, WL 1.24). Mandibles very short and reduced, blunt and edentate; clypeus fairly flat; eyes fairly large (OI 0.47) and protruding, midline of eyes situated well below midline of head, almost extending to clypeal margin; antennae 12-segmented; head wider than long (CI 1.23); in full-face view ocellar triangle situated at posterior head margin and elevated with respect to rest of face; occipital carinae distinct. Mesoscutum in dorsal view as wide as long (MSNI 1.14), scutellum in dorsal view broadly tapering from anterior to posterior end, dorsoposterior part rounded; metanotum not protruding from below scutellum; dorsal face of propodeum almost as long as posterior face; propodeal spines absent; petiole in dorsal view oval, laterally rounded, in lateral view anteriorly greatly tapering; subpetiolar process absent; postpetiole fairly flat and short, lacking median impression. Head sculpture reticulate; mesoscutum with very fine longitudinal carinulae; otherwise sculpture more or less shiny to aciculate; regular appressed to decumbent pubescence, and a few longer setae on face, mesoscutum, and scutellum; remaining pilosity as in queen. Color brown.

References based on Global Ant Biodiversity Informatics

 * Blaimer B. B., and B. L. Fisher. 2013. Taxonomy of the Crematogaster degeeri-species-assemblage in the Malagasy region (Hymenoptera: Formicidae). European Journal of Taxonomy 51: 1-64.
 * Donisthorpe, Horace. 1946. The Ants (Hym. Formicidae) of Mauritius. Annals and Magazine of National History. Ser. 11. 13:25-35.
 * Fisher B. L. 1997. Biogeography and ecology of the ant fauna of Madagascar (Hymenoptera: Formicidae). Journal of Natural History 31: 269-302.
 * Fisher B. L. 2003. Formicidae, ants. Pp. 811-819 in: Goodman, S. M.; Benstead, J. P. (eds.) 2003. The natural history of Madagascar. Chicago: University of Chicago Press, xxi + 1709 pp.
 * Fisher B. L. 2005. A new species of Discothyrea Roger from Mauritius and a new species of Proceratium Roger from Madagascar (Hymenoptera: Formicidae). Proceedings of the California Academy of Sciences (4)56: 657-667.
 * Mamet R. 1954. The ants (Hymenoptera Formicidae) of the Mascarene Islands. Mauritius Inst. Bull. 3: 249-259.
 * Olson D. M., and P. S. Ward. 1996. The ant fauna (Hymenoptera: Formicidae) of Kirindy Forest (tropical dry forest) in western Madagascar. Pp. 161-164 in Ganzhorn, J. U., Sorg, J.-P. (eds.) Ecology and economy of a tropical dry forest in Madagascar. Primate Report 46-1. Göttingen: German Primate Center (DPZ), 382 pp.
 * Soulié J., and L. D. Dicko. 1965. La répartition des genres de fourmis de la tribu des "Cremastogastrini" dans la faune éthiopienne et malgache. Hymenoptera - Formicoidea - Myrmicidae. Ann. Univ. Abidjan Sér. Sci. 1: 85-106.