SUBFAMILY DORYLINAE - Subgenus Anomma comparative study and revision 2002
|
|
The Ants of Africa SUBFAMILY DORYLINAE - Subgenus Anomma comparative study and revision 2002 |
| Subgenus Anomma introduction |
This I offer as a step towards revision of
the status of the members of the subgenus Anomma, based on
specimens sent to me and literature studies, especially the detailed
review of historic literature and of specimens by Raignier & van Boven
(1955). The main constraint on the latter was that they examined only
specimens from the Congo Basin (old Belgian Congo); either collected by
them around Yangambi, or held in the Royal Museum of the Congo in
Tervuren, Belgium. It should be understood that my revision is not based
on an examination of type specimens or other material held in the great
museums. I hope, however, that it will meet my primary objective for the
whole website, that is to enable a field worker or others without easy
access to museum collections to identify the specimens before them
NOTE - it seems from Raignier & van Boven (1955) that only one species, Dorylus (Anomma) wilverthi, can be definitively stated as having all three life forms, male, female and workers, collected together from a nest (by them). They described how the finding of dealated males in migrating columns does not guarantee the males are associated with the workers in the column, instancing an occasion when they found a male of Dorylus (Typhlopone) in a wilverthi column. Thus, what from the literature appears to be perhaps the best known and most widespread member of the subgenus, Dorylus (Anomma) nigricans Illiger, actually is definitively known solely from the male. The vast majority of the references to "nigricans" most probably should be given under the definitive name of the worker described as Dorylus (Anomma) burmeisteri by Shuckard (1840c: 26).
Raignier & van Boven (1955) also emphasise the problem with evaluating the merits of the numerous descriptions of varieties made by the early taxonomists. Differences in colour were used to justify descriptions of new "varieties", such as pallidus and rubellus, but often the author had seen only one or very few specimens. Raignier & van Boven described how, in their studies of colonies in the field, it was not uncommon to see pale specimens, simply because the individual ants were not fully matured. To illustrate this, the illustration (right) shows several specimens taken by Professor S. Uehara from a migrating Driver Ant column at Mahale in Tanzania. As always - a picture is worth a thousand words!
NIGRICANS subgroup
In Bolton (1995) there is a blanket list of the following under the main
species name nigricans :-
nigricans s.s. type locality Sierra Leone (Illiger, 1802;
in subgenus by Emery, 1895, illustrated) named solely from a male
specimen, with no associated worker or queen stages - see
nigricans;
subspecies arcens (and its synonym pubescens, Roger,
1861a) from Liberia (Westwood, 1847b, illustrated worker,
describing the ants in the paper by T.S. Savage, 1847; also illustrated by
Santschi, 1912b) Cape Palmas; burmeisteri (Shuckard, 1840; also
illustrated by Santschi, 1912b) from Sierra Leone, collector D.F.
Morgan; hybrida (unavailable name of variety of burmeisteri,
Santschi, 1912b, illustrated; named as hybridus by Wheeler, 1922))
from Senegal, collcted at Casamance, by Claveau; pallidus
(Santschi, 1921c) from Cameroun; rubellus (Savage, 1849;
reduced to variety by Emery, 1895j; see Wheeler, 1922) from "West
Africa" but actual type locality seems to be Mpongwe District, Congo;
sjoestedti (ssp. by Emery, 1899e; raised to species by Wasmann,
1913, reduction back to ssp. unclear) collected by Y. Sjöstedt;
sjoestedtiwilverthi (as a variety, Wasmann, 1917) from Cameroun
collected at Grand Batanga, by G. Schwab; and terrificus (as a
variety, Santschi, 1923e) from Zaïre; all forms known (see
Bolton, 1995).
Some light on the situation may be in the Haldeman (1849a) paper on
Savage's collection of rubella "red drivers" from Gabon,
with a column amongst which were three males; this is at
.
Haldeman, however, did write "if Dorylus nigricans is taken
as the male of rubella"
Wasmann (1904b) reviewed what Dorylus (Anomma) burmeisteri and
what he regard as the then known varieties. This is at
.
Santschi (1930a) provided what he called a description of the neuters of
Dorylus (Anomma) nigricans. This is at
.
However, Santschi makes no reference to the collections (from Bamako, Mali,
then French Sudan, by J. Andrieu) as including a queen, let alone the
male, which Santschi noted as still unknown. He also provided a list of
what he regarded as stirps and varieties of nigricans.
Raignier & van Boven (1955) gave an extensive description of the confusion, often contradictory and, ultimately unsatisfactory of the studies of Anomma specimens from 1850 to 1933, and settled for nigricans having three definitive subspecies, arcens, burmeisteri (with the varieties hybridus, molestus, ornatus, pallidus, rubellus and terrificus) and sjostedti (with the varieties rufescens, sjostedti-wilverthi).
As my purpose is to facilitate ease of separation of specimens, I have chosen to separate those that I have now seen, from the fresh material sent to me from Cameroun, Guinea and Tanzania, plus my own work at CRIN, Nigeria, into the following "species", drawing extensively on the descriptions cited and given by Raignier & van Boven (1955). In general, I am happy that the combination of findings from widely separated locations and, as the material sent to me included specimens of all morphs, of the characters of the majors and minors gives credence to my attempt. In October 2003, I received specimens from Uganda and Tanzania that added weight, as they included wilverthi and, excitingly, what possibly is the first specimen of a major of mayri, this, as predicted by Santschi (1912b), is the largest major I have seen, rivalled only by titan (in the gerstaeckeri group and very different).
Species known only from sexual stages
Dorylus
(Anomma) bishyiganus van Boven - queen
Dorylus
(Anomma) funereus Emery - male; junior synonyms acherontus
Santschi, pardus Santschi, stygis Santschi and zumpti
Santschi
Dorylus
(Anomma) niarembensis van Boven - queen
Dorylus
(Anomma) nigricans Illiger - male
Dorylus
(Anomma) stanleyi Forel - male
The overall size, TL ca 19 mm, and mandible shape would appear to place Dorylus atratus Smith in subgenus Alaopone and not Anomma as given by Emery (1895j: 723).
I have tried to separate what is known of the males on MALES.
Species known from worker stages
The division into two main groups - the NIGRICANS group and the GERSTAECKERI group - is something I have based on the separation identified by Raignier & van Boven (1955) of those with slender antennae, notably with their "scape index" = (scape width/scape length) X 100, being < 20; and, those with shorter, stouter antennae, "scape index" > 20. The further division into sub-groups is something I have adopted, although Raigner & van Boven were able to examine and separate the queens of four species - molestus, wilverthi, burmeisteri and sjoestedti - all within the NIGRICANS group and all separable as workers into my "sub-groups".
Morphology pattern graphs on species pages
With the specimens I collected or was able to examine at CRIN, I made measurements using a stage micrometer. With the specimens sent to me from Guinea, Cameroun, Tanzania and Uganda, I made measurements of the images obtained by scanning (not so accurate). The data were entered in an Excel worksheet and normalized by converting each measurement into a % of the total length for the specimen. The graphs so produced have been visually compared as a means of attempting to separate the different forms.
The montages of the minima morph are intended to emphasis the obvious variations between species and the scales are indicative rather than precise due to the small size of the morphs.
Provisional Key to major workers following new definitions
of species
Note - the illustrations are not all at the same scale and the colours are
as photographed using an incandescent low voltage light source (the
species pages include images of the specimens as scanned with a
fluorescent white light source).
I have included a column of full face views of the minima morph; this
appears to confirm the merit of the grouping and sub-grouping of the
species.
The distribution of the subgenus as known does not extend outside the
sub-Saharan forest zone; across from extreme West Africa to Kenya, Uganda
and Tanzania. Thus, where I use the term "panafrican" it relates
only to within the forest areas.
Dorylus (Anomma) erraticus (F Smith) - is known only from a poor description of a minor worker, with an original anomalous type location given as "New Guinea".
| - | Diagnostic feature for major | minima
faces (not to scale) |
Species |
| 1 | Antennal scape long and slender
(width no more than 20% of length), funiculus segments also slender  |
Most relatively narrow and with limited if any pilosity | NIGRICANS group 2 |
| -- | Antennal scape short and broad
(width more than 20% of length), funiculus segments short and broad,
more bead-like   |
Most relatively wide and with quite dense pilosity | GERSTAECKERI group 8 |
| 2 | Head shape trapezoidal, posterior
margin deeply scalloped, long slender mandibles; very bulbous in profile |
- | ARCENS sub-group 3 |
| -- | Head shape otherwise | - | 5 |
| - | ARCENS sub-group | - | |
| 3 | Head with pronounced posterior
angles, each bearing a sharp out-turned tooth |
 |
Panafrican but seemingly more common in eastern areas - Dorylus wilverthi |
| -- | Head with or without pronounced posterior angles but never with distinct teeth at the angles | - | 4 |
| 4 | Head and body matt; colour very dark
brown, near black
|
 |
Western areas - from Liberia round to Gabon - Dorylus arcens |
| -- | Head and body shiny; colour dark
chestnut red |
 |
Zaïre & Guinea - Dorylus terrificus |
| -- | Head shiny but lateral alitrunk,
propodeum and gaster more matt; colour red-brown, with yellow-brown
areas, notably on the gaster |
 |
Cameroun & Uganda - Dorylus mayri |
 |
- | - | |
| 5 | Petiole with dense spiculate
sculpturation and decumbent hairs on posterior margin |
With rounded sides and occipitum | BURMEISTERI subgroup - 6 |
| -- | Petiole relatively short with all
edges rounded and dorsum widening so posterior about 30% wider than
anterior, weakly sculptured |
With relatively straight sides and sharp occipital margin | SJOSTEDTI subgroup 7 |
| - | BURMEISTERI subgroup | - | |
| 6 |
Head widest at mid-length; petiole
only moderately long and with distinct posteroventral processes;
propodeal spiracle ovoid vertical |
With no more than
sparse pilosity on alitrunk |
Panafrican but primarily western - Dorylus burmeisteri |
| -- | Head widest at anterior or within
one-eighth of head length ; petiole quite long and narrow and dorsum
with parallel sides; without distinct posteroventral processes;
propodeal spiracle near circular |
Alitrunk with quite
dense pilosity |
Panafrican - Dorylus molestus |
| - | SJOESTEDTI subgroup | - | |
| 7 | Overall colour red-brown or darker,
matt |
Relatively broad, shiny |
Congo Basin - Dorylus sjoestedti |
| -- | Overall colour of major red
(anterior of head with dark border, matt in front, shiny behind) with
smaller morphs yellow to yellow-brown |
Seemingly relatively pale, yellow-brown | Congo Basin - Dorylus rufescens |
| -- | Overall colour red and shiny ;
petiole with bifurcate ventral process |
Relatively long and
narrow, quite densely sculptured |
Congo Basin east into western Tanzania & Uganda - Dorylus ornatus |
|
Antennal scape short and broad (width more than 20% of length), funiculus segments short and broad, more bead-like | - | - |
| 8 | Head rectangular, straight sided, petiole globulose | Face with near hemispherical occipitum and inconspicuous pilosity on antennae | TITAN sub-group 9 |
| -- | Head with posterior narrowed and petiole not globulose | Face otherwise and/or antenna with obvious pilosity | 11 |
| - | TITAN sub-group | - | |
| 9 | Large species, TL of major ca 14 mm;
major with very distinctive large rectangular head with parallel
slightly sinuous sides |
 |
Zaïre & Guinea - Dorylus titan |
| -- | Small species; TL > 9 mm; petiole
distinctly globular |
10 | |
| 10 | Major TL ca 8 mm; major with dull
appearance, especially on head, due to dense ground spiculation |
 |
Tanzania - Dorylus ueharae new species |
| -- | Major TL > 9 mm; overall shiny
without ground sculpture of dense spiculation |
 |
Guinea - Dorylus lamottei |
| - | - | - | |
| 11 | Head widest at extreme front end;
petiole rectangular with decumbent rear-pointing hairs on posterior
margin |
With near hemispherical
occipitum, quite slender scapes |
VICTORIAE subgroup - panafrican - Dorylus victoriae |
| -- | Head widest at 1/3 of length or further back | With distinct occipital angles, impressed occipitum and thick scapes | 12 |
| 12 | Head near square, widest at about
1/3 of length, posterior margin a shallow scallop, corners rounded;
mandibles quite long, slender and sharp; petiole length and breadth
sub-equal |
Head with HL < 1.25
HW and with widely rounded occipital angles |
KOHLI sub-group - 13 |
| -- | Head widest at mid-length, sides
smoothly convex, posterior deeply scalloped with acute angles; mandibles
relatively short and thick |
Head with HL > 1.25
HW and with near square rounded occipital angles |
14 |
| - | KOHLI sub-group | - | |
| 13 | Head widest at about 1/3 length,
posterior margin a shallow triangle; propodeal spiracle circular;
mandible relatively long |
|
West Africa & Congo Basin - Dorylus kohli |
| -- | Mandibles long and narrow, head
widest about midlength, posterior margin shallowly scalloped. propodeal
spiracle a small oblique oval, colouration dark but brighter than kohli |
 |
Panafrican - Dorylus militaris |
| - | - | - | |
| 14 | Head narrowing < 60%; relatively
shallow in profile; mandibles short and thick, with a subapical tooth;
relatively dull matt; propodeum spiracle small and circular |
 |
EMERYI subgroup - West Africa & Congo Basin - Dorylus emeryi |
| -- | Head shiny, narrowing to ca 50%;
shiny, propodeal spiracle ovoid |
- | GERSTAECKERI sub-group - 15 |
| - | GERSTAECKERI sub-group | - | |
| 15 | Head with quite sharp posterior narrowing | - | 16 |
| -- | Head with limited posterior narrowing | - | 17 |
| 16 | Petiole with long triangular ventral
process; head a uniform dark red-brown |
 |
Panafrican - Dorylus gerstaeckeri |
| -- | Relatively small TL no more than 9
mm; head red-brown with black anterior margin; posterior of head shiny |
|
eastern Zaïre, Uganda & Tanzania - Dorylus indocilis |
| 17 | Head and specially body dull matt,
head narrowing less |
- | West Africa & Congo Basin - Dorylus opacus |
| -- | Head width and length similar, with
more pointed posterior angles, mandibles short and quite straight  |
 |
southern Congo & Angola - Dorylus congolensis |
 |
Subgenus Anomma introduction | © 2007 - Brian Taylor CBiol
FIBiol FRES 11, Grazingfield, Wilford, Nottingham, NG11 7FN, U.K. |
href="anomma2002.htm"