Key to Crematogaster degeeri species assemblage workers

This worker key is based on: Blaimer, B.B. & Fisher, B.L. 2013. Taxonomy of the Crematogaster degeeri-species-assemblage in the Malagasy region (Hymenoptera: Formicidae). European Journal of Taxonomy 51: 1-64 (DOI 10.5852/ejt.2013.51).

Characterization
The species in the assemblage are part of the Crematogaster castanea species-group (Subgenus Crematogaster).

Blaimer and Fisher (2013) provided the following regarding this species-assemblage: No morphological characters that unite these ants have been discovered to date. This group was referred to in Blaimer (2012b) as the “Crematogaster degeeri-sewellii group”; after subsequent broadening by Blaimer (2012d) to include a few African species, it was hence dubbed the “C. castanea-group”. This grouping likely does not form a clade, but rather represents a group of loosely related species that may have closer affinities with African species (but see phylogeny in Blaimer 2012b). We choose here to revert to a description of the Malagasy species in this group only, since our taxonomic insight into the related African species is not yet sufficient. Most species in the C. degeeri-assemblage occur in Madagascar only, but three species are also found in the wider Malagasy region, including the Indian Ocean Islands of Comoros, Mayotte and Mauritius. The group is not present in the Seychelles.

The natural history and ecology of species within this group do not follow a common theme but are highly diverse. The C. degeeri-assemblage includes arboreal species nesting in dead twigs or branches, as well as ground-dwelling species found in nests under stones or in the soil. Ground-nesting is rather atypical for Crematogaster ants, which often dominate the canopy. All major macrohabitats are occupied by one or the other representative of the C. degeeri-assemblage in Madagascar: dry and spiny forests, littoral forest, rainforest, montane forest, savannah and grasslands, as well as coastal and mangrove habitat. A few species further appear to adapt quite well to urban or disturbed areas.

You may also be interested in


 * Crematogaster 
 * Key to Crematogaster species groups of the Malagasy region
 * Key to Crematogaster degeeri species assemblage queens
 * Ants of Madagascar

1

 * Propodeal spines absent, reduced to small tubercules or denticles, or short triangular spines with SPI < 0.07; if very rarely propodeal spines spiniform and longer (SPI 0.08-0.10), then small species (HW 0.72-0.88, WL 0.79- 0.91), color dirty-yellow, montane rainforest habitats . . . . . 2


 * Propodeal spines longer, distinctly spiniform and SPI > 0.07; size and color variable; all habitats . . . . . 9

2
return to couplet #1
 * Eyes small (OI < 0.21) and largely confluent with lateral head margin . . . . . 3


 * Eyes larger (OI > 0.20) and distinctly protruding from lateral head margin . . . . . 6

3
return to couplet #2
 * Pronotum dorsally with a distinct median longitudinal groove, medium to large species (HW 0.98-1.43, WL 0.98-1.48) . . . . . Crematogaster mafybe


 * Pronotum dorsally without median longitudinal groove, size variable . . . . . 4

4
return to couplet #3
 * Propodeum with spines absent or at most small tubercules (SPI 0.00) . . . . . Crematogaster lobata


 * Propodeum with short triangular spines or sharp minute denticles . . . . . 5

5
return to couplet #4
 * Antennal scapes very short (SI 0.67-0.75), not reaching head margin; mesonotum usually with posterolateral denticles . . . . . Crematogaster masokely


 * Antennal scapes variable, but usually longer (SI 0.69-0.82) and about reaching head margin; mesonotum usually without posterolateral denticles . . . . . Crematogaster dentata (in part - also ) (in part - also )

6
return to couplet #2
 * Eyes very large (OI 0.24-0.29), situated above midline of head in full-face view; antennal scapes mostly longer (SI 0.77-0.87), reaching or surpassing head margin; bicolored: head and thorax yellowish to dark orange, metasoma with A4-7 brown or black . . . . . Crematogaster sewellii


 * Eyes mostly smaller (OI 0.20-0.26), usually situated at midline of head in full-face view; antennal scapes variable, but often shorter (SI 0.69-0.83), just about or not reaching head margin; color variable . . . . . 7

7
return to couplet #6
 * Propodeum usually distinctly set off from promesonotum in lateral view and often with posterolateral denticles; promesonotum with sparse erect pilosity ( < 8 setae); petiole often much wider than long (PTWI 1.18-1.52), and strongly flared . . . . . 8


 * Propodeum not distinctly set off from promesonotum (in lateral view), never with distinct posterolateral denticles; promesonotum usually with abundant erect pilosity (>8 setae); petiole not much wider than long (PTWI 0.95-1.31), moderately flared . . . . . Crematogaster dentata (in part - also ) (in part - also )

8
return to couplet #7
 * Medium-sized species (HW 0.86-1.03, WL 0.92-1.08); propodeal spines short and triangular (SPI 0.03-0.07); pronotum with sharp lateral margins . . . . . Crematogaster malahelo


 * Small species (HW 0.72-0.88, WL 0.79-0.91); propodeal spines longer (SPI 0.06-0.10); pronotum lacking sharp lateral margins . . . . . Crematogaster alafara

9
return to couplet #1
 * Body color dirty to bright yellow . . . . . 10


 * Predominant color either orange, brown or black . . . . . 11

10
return to couplet #9
 * Medium to large species (HW 0.87-1.03, WL 0.98-1.22); antennal scapes very long (SI 0.91-1.01), easily surpassing head margin . . . . . Crematogaster bara


 * Small species (HW 0.60-0.86, WL 0.66-0.93); antennal scapes short (SI 0.71-0.83), not or about reaching head margin . . . . . Crematogaster maina

11
return to couplet #9
 * Head distinctly broader than long (CI 1.10-1.19); propodeal spines longer (SPI 0.10- 0.26); tricolored: orange-red, yellow and black . . . . . Crematogaster tricolor


 * Head not much broader than long (CI 1.01-1.13); propodeal spines shorter (SPI < 0.16); uniformly colored or bicolored . . . . . 12

12
return to couplet #11
 * Mesonotum often with posterolateral denticles (Fig. 5C); in lateral view distinctly set off from propodeum (Fig. 5C); eyes large (OI 0.22-0.26); propodeal spines longer (SPI 0.10-0.16); erect pilosity on promesonotum often sparse ( < 8 long erect setae) (as e.g. Figs 5C) . . . . . Crematogaster degeeri


 * Mesonotum variable, but more often without posterolateral denticles, and thus in lateral view not as distinctly set off from promesonotum (Fig. 5D); erect pilosity usually more abundant ( > 8 long erect setae) (as in Fig. 5D, E); propodeal spines shorter (SPI < 0.12) . . . . . 13

13
return to couplet #12
 * Propodeum with a distinct short dorsal face, and with a transverse impression (Fig. 5E); sculpture on pronotum carinulate or reticulate (Fig. 5E); petiole oval, fairly slender; (PTWI 0.95-1.14); propodeal spines longer (SPI 0.07-0.12) . . . . . Crematogaster ramamy


 * Propodeum usually without a distinct dorsal face, never with transverse impression (Fig. 5F); sculpture on propodeum rugulose or aciculate (Fig. 5F); petiole variable, but often wider (PTWI 0.95-1.31); propodeal spines usually shorter (SPI 0.01-0.10) . . . . . Crematogaster dentata (in part - also ) (in part - also )