Crematogaster sp: Cocktail ants

MYRMICINAE

The Genus Crematogaster (Cocktail ants)


Typical ‘carton’ nest built by Crematogaster ants; this one in the hedgerows near Albertinia
Two features in particular distinguish Crematogaster from all other ants: first, the unique nests that many species build from chewed-up vegetable matter, and secondly, the manner in which they aggressively raise their gasters [or ‘cock their tails’] when danger threatens. Ants of this genus have a uniquely-constructed link between thorax and gaster that allows them to do this – see diagram below.


There are about 43 species in Southern Africa, of which the most common are the Black Cocktail ant (Crematogaster peringueyi),the Brown Cocktail ant (Crematogaster melanogaster) and the Red Cocktail ant (Crematogaster castanea), which occurs along the south and east coasts and up into the northern interior of South Africa. The genus in Africa is in a fairly severe taxonomic mess, but includes a large number of forest species as well as thorn-dwelling species in savanna habitats.
Crematogaster peringueyi (Emery, 1895):
Black cocktail ant

Crematogaster melanogaster (Emery, 1895):
Brown cocktail ant

Crematogaster castanea (F. Smith, 1858):
Red cocktail ant


Black cocktails are commonly found in strandveld and moister fynbos, while their reddish-brown black-gastered cousins (C. melanogaster) prefer more arid habitats. The Red cocktail ant (C. castanea) prefers forested or moister habitats. Note that C. castanea are massively varied, with several subspecies and more ‘varieties’ than we can count.

Size: Some confusion exists around the size of the ants. Some of the species are quite variable; C. peringueyi can vary [but not in the same nest, please note – these variations are in separate colonies] from 3.5 to 5 mm in length.





All three species are diurnal and swarm aggressively when disturbed. Their bite can be painful, but their mandibles are too small and weak to draw blood. Despite this none of these species is able to resist invasive ants, especially Argentine ants (Linepithema humile) and, interestingly, they never seem to share a habitat with indigenous Pugnacious ants (Anoplolepis sp.), and are always fiercely antagonistic towards them.

Some useful photos of C. peringueyi can be found at these links:

www.ispotnature.org/node/600786
www.ispotnature.org/node/524985
www.ispotnature.org/node/641417
www.ispotnature.org/node/695810
www.ispotnature.org/node/707932

A couple of good photos of C. castanea are at these:

www.ispotnature.org/node/587881
www.ispotnature.org/node/598371

Crematogaster transvaalensis (Forel, 1894):
Small black cocktail ant




This is the only Southern African Crematogaster that belongs to the sub-genus Orthocrema. Based on characteristics not visible to the naked eye, the classification essentially places this small species amongst the most ‘primitive’ of the genus. Usually found under stones in subterranean nests, the species does not build the carton nests associated with the genus.

The workers are all the same size and measure about 2.5 to 2.8 mm; the colonies are small. The bodies are black with limited pilosity, with brown to reddish mandibles and brown legs.

The name means ‘from the Transvaal’, a complete misnomer as, although never common, the ants are widespread from the Western Cape fynbos to Limpopo.



Crematogaster orobia (Santschi, 1919)
Matroosberg cocktail ant


A small species (workers from 2.6 to 3.2 mm), the ants are black with dark brown mandibles, clypeus and tarsi [lower legs]. Fairly hairless; gaster smooth and shiny. At a microscopic level the petiole joint is more complex than in C. transvaalensis, but otherwise C. orobia is hard to tell apart from its distant cousin. However, the ant is rare and has only been found in the Western Cape at altitudes above 1500 m, so if you find black Crematogaster under stones anywhere above the Western Cape snowline they will with 99% certainty be C. orobia, not C. transvaalensis.



Survive invasive species:

Linepithema humile       : Argentine ants       : No
Pheidole megacephala  : House ants            : unknown
Lepisiota capensis         : Small Black ants    : unknown

2 comments:

  1. Hi, I was just wondering which are the thorn-dwelling species and on what Acacia species are these found? Are these examples of plant-ant mutualisms?

    ReplyDelete
  2. What a wonderful resource this is! Thanks you.

    ReplyDelete

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