Crematogaster

Wheeler, W. M., 1922, The ants collected by the American Museum Congo Expedition., Bulletin of the American Museum of Natural History 45, pp. 39-269 : 150-151

Crematogaster Lund

Crematogaster is one of the largest and most sharply defined genera in the family Formicidae. The species are all small, with monomorphic worker, decidedly larger female, and the male usually as small as the worker. The worker and female have 10- or 11-jointed antennae, those of the male are usually 12-jointed. All the phases can be readily recognized by the peculiar structure and articulation of the petiole and postpetiole. The former does not bear a node but is more or less flattened above, the latter is short and articulated to the anterodorsal surface of the gaster, instead of to its anterior end as in other ants. The gaster, moreover, is in the worker and male subtriangular or subcordate, with pointed tip, and its upper surface is concave or more or less flattened, its ventral surface more convex and protuberant. These peculiarities in the structure of the abdomen enable the workers of many species to turn the gaster forward over the thorax and head, so that they are sometimes called "acrobat ants." As a rule, the sting is feebly developed. The anterior wings of the male and female have a discoidal and a single closed cubital cell.

The species of Crematogaster all form populous colonies which nest in the ground, under stones, in logs, the cavities of living plants, or in peculiar carton nests attached to the branches or trunks of trees. This habit of making carton nests is best seen in the tropical species, but traces of it survive even in the species inhabiting temperate regions, such as the North American C. lineolata (Say) . Many of the species have rank and disagreeable odors.

The genus is cosmopolitan (Map 22), though the species scarcely enter the colder portions of the north and south temperate zones. Our common C. lineolata (Say) of North America occurs, however, as far north as Nova Scotia. The vast majority of species are confined to the tropics, being particularly numerous in the Neotropical and Ethiopian Regions. The African forms are so numerous and so variable that they constitute a veritable welter of subspecies and varieties. Mayr, Forel, Arnold, and Santschi have all dispaired of reducing this chaos to order. Unfortunately the portion of Arnold's work dealing with the South African species has been postponed by the war. He has, however, kindly written me concerning certain necessaly changes in the synonymy of several of the species and I have adopted his interpretations in the list of Ethiopian species (Part VIII). Dr. Santschi, who has given more attention to the African species of Crematogaster than any previous author, has generously examined and identified a series of all the Congo forms collected by Lang, Chapin, and Bequaert and has written the descriptions of several new forms. In the meantime he has published a revision of the subgenera of Crematogaster .1 Forel was the first to begin the splitting of the genus, but Santschi has added several new subgenera. A translation of his table has been included in the key to the genera and subgenera of Myrmicinae. Santschi has arranged these various subgenera according to their natural affinities in the following sequence:

1. Decacrema

2. Orthocrema

3. Eucrema

4. Neocrema

5. Sphaerocrema

6. Crematogaster , sensu stricto

7. Atopogyne

8. Paracrema

9. Xiphocrema

10. Physocrema

11. Oxygyne

12. Nematocrema

Of these, at least seven, Decacrema , Orthocrema , Sphaerocrema , Crematogaster , Atopogyne , Oxygyne , and Nematocrema occur in the Ethiopian Region. In the Congo material before me only Sphaerocrema , Crematogaster , Atopogyne , and Nematocrema are represented.