AENICTINAE: the False army ants

This monogeneric sub-family was raised by Bolton in 1990, when it was decided that the genus Aenictus was inappropriately placed in the Dorylinae sub-family. The name comes from the Latin ‘aenigma’, meaning ‘puzzling’ or ‘ambiguous’. For a long time the genus was known only from winged male specimens; indeed, there are several species that are still only known from a handful of male specimens, no workers ever having been collected.

The Genus Aenictus (False army ants)

Aenictus, the ‘enigma ants’, are eyeless, ground-dwelling ants that occur across the Old World, from Africa into China and down to Australia. Mostly tropical, there are 181 described species, with 37 of these in Africa. There are several species awaiting description, but there are also a number of obscure species that might be combined in future.
The African species are all specialised predators of other ants, especially eggs, larvae and pupae. The colonies are very large and prey species are overcome by sheer weight of numbers. Raids are mounted upon nearby ant colonies, when large numbers of workers attack and assist each other in collecting and removing their prey. The columns of attacking and/or triumphantly returning ants resemble the habits of army ants such as Dorylus, hence the common name, ‘False army ants’ (‘True’ army ants move in nomadic columns that attack and consume anything edible that they find along the way). Columns move half-concealed through leaf litter, etc; it is not known whether the nests are permanent, or whether the ants are occasionally nomadic – the latter seems probable. 
Most species are very small (>2mm) to medium-small (>5mm), another feature which distinguishes them from true army ants. The antennae are 10-segmented [scape + 9], with a shortened, often curved scape; no eyes; much reduced clypeus bringing the antennal sockets very close to the front of the head; the two-segmented petiole creates a superficial resemblance to ants of the Myrmicinae sub-family. In most species there are ventral processes on the petiole nodes.
The genus is reputed to be monomorphic [all ants are the same size or shape] but this is not so, as some species have major workers that have different head shapes and colouring than the minors. In fact, five of our six local species in which workers have been found are polymorphic, with a smooth gradation from the minors to the (differently shaped) majors.

There are ten species from our region, of which four are so obscure that only males have ever been found; these are not dealt with here, but for the record they are
Aenictus alluaudi 
Aenictus crucifer 
Aenictus fuscovarius
Aenictus inconspicuus

The other six species are described below in descending order of size.

Aenictus eugenii (Emery, 1895):
Eugene’s false army ant

The workers are 3.7 to 4.0 mm long, larger and much darker-coloured than the very similar A. rotundatus, and varying less in size than the workers of that species. The head and alitrunk are a bright castaneous [chestnut-coloured] red with a lighter coloured gaster. The legs are yellowish red, and the sides of the alitrunk and the mandibles are a brownish red.
This species closely resembles A. rotundatus, but apart from size and colour as noted above also differs in that the pilosity is less abundant, but more regularly distributed over the body, and longer. 
The head of A. eugenii is distinctly wider in front than behind. The antennae are proportionately longer than in other species, the scape almost reaching back to the occipital margin, and all the segments of the flagellum are distinctly longer than wide. The alitrunk is narrow, and the sides of the propodeum, mesonotum [middle segment] and petiole nodes are markedly rough and pitted [reticulate-punctate]. The legs are long and slender.
In our region the species is found in KwaZulu-Natal, Mpumalanga, Limpopo, North-West and the Free State, as well as Zimbabwe.
We presume that the species is named after the famed naturalist, Eugene Marais (1871 – 1936); whom Emery met as a young man.
Fantastic pics by Wynand Uys are on iSpot at: 

Aenictus rotundatus (Mayr, 1901):
Golden false army ant

The workers range from 2.3 to 3.8 mm in length. How such a wide range – where the majors are nearly twice as large as the minors – can be described as ‘monomorphic’ is ridiculous, especially as the majors have wider heads and are darker in colour than the minors. In fact the species is polymorphic, with a continuous range of sizes from largest to smallest. The body colour is golden red, with some ants having a paler basal gaster segment. Smooth and very shiny, with only a slight roughness [reticulate-punctate] on the sides of the alitrunk and petiole. Pubescence absent except on the funiculi of the flagellum. There is a long, yellowish and rather sparse pilosity on the petiole and gaster, and less regular and scantier, on the head, scape and alitrunk.
Major workers’ heads are as wide as they are long, while minors’ heads are about 20% longer than wide. The mandibles are fairly long with one large apical tooth and up to 9 smaller teeth. In the antennae, the first to 3rd funiculi are longer than wide, 4th to 6th as wide as long, 7th and 8th longer than wide and the ‘club’ about 2.5 times longer than wide [see A. eugenii above, where all the segments are longer than wide]. There are angular or blunt projections underneath each petiole node. The legs are long but not as proportionately long as in A. eugenii.
In our region the species is found in the Western, Eastern and Northern Cape, KwaZulu-Natal, Gauteng, Botswana and Zimbabwe.
‘Rotundatus’ means ‘rotund’ or ‘round-shaped’ and presumably refers to the shape of the major workers’ heads.
Fairly good pics by Ricky Taylor, which I erroneously originally identified as Solenopsis puntaticeps, are on iSpot at

Aenictus furibundus (Arnold, 1959):
Frenzied false army ant

The workers range from  2.4 to 3.7 mm; as above, they are polymorphic, not monomorphic, with majors’ head wider in front than behind, minors’ heads symmetrical on the long axis.
The colour is reddish ochre, with a lighter gaster; there is a sparse yellow pilosity on the whole body. The mandibles have a large apical tooth and up to seven smaller teeth. The colouring is similar to A. eugenii, but the range of sizes is much wider; the range of sizes is similar to A. rotundatus but the colouring is much redder. The colonies are found under stones and are very large.
Zimbabwe only.
The name ‘furibundus’ simply means ‘frenzied’, ‘frantic’ or even ‘raving’, presumably a reference to their aggressive behaviour.
No pics available yet.

Aenictus steindachneri (Mayr, 1901):
Hairy false army ant

In every way very similar to A. rotundatus [see above], including the range of polymorphic sizes, but the thoracic region is fully clothed in fairly dense, backward-facing pubescence.
Named by Mayr after the zoologist Dr Franz Steindachner (1834 – 1919).
This ant has only been collected in the Free State.
No pics available yet.

Aenictus mariae (Emery, 1895):
Maria’s false army ant

The ants vary in size from 2 to 3 mm; the majors differ from the minors in the shape of their heads, so this species is yet again not monomorphic. The majors are reddish ochre in colour, with convex head sides and the sides of the thorax dull; the minors are straw-yellow with darker margins to the head and mandibles. The pilosity is scanty; the antennae are shorter than in other species; the legs are shorter and stouter than either A. rotundatus or A. eugenii.
The variety natalensis is more brownish yellow with longer pilosity.
The species is named in honour of Maria Sibylla Merian (1647 – 1717), the first-known female entomologist whose careful studies and illustrations first demonstrated and explained the process of metamorphosis in butterflies, studies that have been described by David Attenborough as ‘the most significant contribution in the field of entomology’.
Found in KwaZulu-Natal, Limpopo and Zimbabwe 
No pics at this stage.

Aenictus rixator (Forel, 1901)
Brawling false army ant

Very small ants, less than 2 mm in length. Dirty yellow in colour with a brownish tint, almost yellowish-red on alitrunk; very smooth and shining, with a fine, yellowish short, sparse pilosity. The heads are rectangular, longer than wide, with narrow, 3-toothed mandibles and petiole nodes longer than wide.
The name ‘rixator’ is Latin for ‘brawler’ or ‘bully’, no doubt accurately reflecting the ants’ behaviour.
KwaZulu-Natal only. 
No pics at this stage.

No comments:

Post a Comment

Please feel free to add any comments, observation etc that might help make this site more useful to more people.