The Ants of Africa
Studies of ant-plant relationships

This is a fascinating story, particularly as it illustrates how important multidisciplinary studies are for the sound understanding of a biological system.

In his first paper, Doyle McKey, relates the beginnings of his study of an "ant-plant", which he names as Leonardoxa africana.(McKey, 1984). This tree had been mentioned by J. Bequaert (1922, p 408) as Schotia africana, a plant with swollen internodes and often inhabited by ants but he found no evidence of it being a true myrmecophyte.

Here, Bequaert's definition of "myrmecophyte" is worth giving. Drawing on the earlier work of Warburg (Warburg, O. 1892. Ueber ameisenpflanzen. Biol. Centralbl., 12, 129-142), it was possible to have three categories:
Myrmecotrophic plants, which provide only food for ants (such as sugary exudates from extrafloral nectaries; special food bodies - the bromatia of fungi; seeds or fruit, etc.).
Myrmecodomic plants, which provide only shelter to the ants - either in normal cavities (such as hollow stalks), or in special swellings, domatia (then called myrmecodomatia).
Myrmecoxenic plants, which provide both shelter and food.

Bequaert himself seems to have preferred simply to use "myrmecophyte" for any plants that "during life are continuously inhabited by certain species of ants". He took some pains to emphasise that, however common, plants, such as the savannah Acacia, where the use by ants of empty insect-induced galls is frequently encountered, are not plants which should be regarded as myrmecophytes. In Africa, he thought the true myrmecophytes to be all restricted to the permanently moist evergreen rain forest. similarly all are perennials and of a woody nature, either bushes, low trees or woody creepers. To be of benefit to the ant colonies there need to be the permanency of a perennial and woody stems add to the solidity of the domatia and the protection given to the ant colonies.

The domatia (derived from the Latin domus, home) that had been recognised were of four types -

  1. With leaf stipules persisting for some time and much swollen, so that their curved over margins enclose a pouch-like cavity, e.g. Macaranga saccifera.
  2. With the leaves with pouches at the base of the blade, e.g species of Cola and Scaphopetalum
  3. With stems which are externally normal but hollowed out for most of their length, e.g Vitex staudti and Barteria dewevrei.
  4. With stems that have fistulose swellings either in the middle of the internodes, e.g. Randia lujae and R. myrmecophyla; in, above, or below the nodes, e.g. Uncaria, Sarcocephalus, Plectronia and Cuviera; or at the base of certain branches, e.g. Barteria fistulosa.

Ants recorded from myrmecophytes

Bequaert (1922, p 406) emphasised that it was necessary to draw a distinction between those ants which were obligatory plant ants, living exclusively in myrmecophytes, and those which had a facultative relationship with the host plant, being only occasionally or accidentally associated with the plant.

Obligate plant ants

Even though the number of ant species that did nest in the domatia of ant plants was low, the number of known obligate plants ant was limited to three species - now all regarded as in the single genus, Tetraponera - T. tessmanni (as Viticicola tessmanni) with its host plant Vitex staudtii; T. aethiops (as Pachysima aethiops) and T. latifrons (as Pachysima latifrons) from various species of Barteria and Epitaberna myrmoecia.

Bequaert thought it likely that some of the African species of Engramma (now split among two genera Axinidris and Technomyrmex) and Plagiolepis which had been collected only from plant domatia might also turn out to be obligate plant ants. See the information below on ant-plants reviewed by Bequaert and my identifications of ants sent to me by the Doyle McKey team.

To this short list now can be added the species, Aphomomyrmex afer, Petalomyrmex phylax and Cataulacus mckeyi studied by Doyle McKey and his colleagues.

Ants in named plants (from Bequaert, 1922; botanical names mostly as given by Bequaert)


Leonardoxa africana (as Schotia africana, p 408) - regarded as a possible myrmecophyte as it has swollen hollow internodes, with the wall pierced by a hole through which ants gain access to the inner cavity. [Now known to be a true myrmecophyte -studied by Doyle McKey and his colleagues].


Macaranga (p 409ff) - two species which have persistent pouch-like stipules, containing nectaries and occasionally occupied by ants. On Macaranga saccifera, an earlier worker, E. Laurent, had found ants inside the pouches of specimens from Kasai District, in north-eastern Zaïre, and once Bequaert found Crematogaster (Atopogyne) africana ssp tibilais workers in some of the stipules; the stipules were not closed with carton and did not contain any brood or coccids.


Cola species (p 414ff) - a few related forms, all with branches and leaves covered with numerous long, stiff erect hairs of a brown or brownish red colour, were found to be myrmecophilous. Of these Cola laurentii, a rather common moderate-sized bush of the Congo Basin, has a pair of basal elongate-oval pouches between the midrib and the first lateral vein. Technomyrmex kohli (as Engramma kohli) was found in the pouches on one occasion (at Uchibango, February, 1915) and some of the plants collected by H. Lang along the Tshopo River, around the northern edges of Kisangani (Stanleyville) were inhabited by Plagiolepis mediorufa.

Scaphopetalum species (p 419ff) - eight species were known with two thought to be myrmecophilous. Scaphopetalum dewevrei was found at Matchacha, Eastern Congo Forest, by Dewèvre to have a fold at the base of the leaves inhabited by "numerous red-brown ants with a black abdomen" [see the specimens from the 2001 collections and separated by me as Technomyrmex laurenti]; and by Luja, at Kondué, to have Technomyrmex lujae (as Engramma lujae) in the pouches. Scaphopetalum thonneri, widespread in Cameroun and the Congo Basin, had a peculiar pouch, which on one occasion was found by Mr Lang, at Niapu, Zaïre, to contain both T. lujae and Technomyrmex kohli (as Engramma kohli).


Buchnerodendron speciosum (p 423) - this common bush or small tree of the primary rain forest, and forest galleries along savannah streams, was observed by Kohl, at Romeé, near Kisangani (Stanleyville) to have hollow branches inhabited by small black ants, All the instances of ants were of (probably) Crematogaster (Crematogaster) impressa (given as Crem. excisa).

Barteria fistulosa (p 438-9) - Tetraponera aethiops, Tetraponera anthracina, Tetraponera emacerata (as T. oberbecki and as prelli variety odiosa), Tetraponera latifrons, Tetraponera mocquerysi and Tetraponera ophthalmica; Crematogaster (Crematogaster) impressa (as ssp of excisa), Crematogaster (Crematogaster) impressiceps and Crematogaster (Sphaerocrema) striatula.

Barteria dewevrei (p 441) - Tetraponera aethiops, Crematogaster (Atopogyne) africana variety, Crematogaster (Atopogyne) africana variety schumanni.


Epitaberna myrmoecia (p 442) - Tetraponera aethiops.


Clerodendron possibly species excavatum (p 443) - hollow stems found at Penge, Ituri River by Bequaert contained a small, unidentified ant; at Bukoba in western Tanzania, Crematogaster were found in Clerodendron formicarium.

Vitex staudtii (p 446) - Tetraponera tessmanni (as Viticicola tessmanni).


Grumilea venosa (p 452) - reported by Dewèvre, from Leopoldville and Bokakata (Zaïre) as always inhabited by numerous black ants.

Uragoga species ? (p 453) - swollen stipules at the base of paired leaves found to contain coccids tended by Crematogaster (Sphaerocrema) striatula variety obstinata, which had built tents of vegetable material to shelter the coccids. Possibly not a true myrmecophyte.

Uncaria africana (p 454) - the myrmecodomatium consists of the enlarged and hollow basal internodes of two opposite, lateral branches; the cavities in the swellings communicate with the hollow, very slightly swollen node of the main branch (illustrated, p 457). All the instances of ants were of Crematogaster (Crematogaster) impressa (as Crem. excisa ssp andrei).

Sarcocephalus species (p 459) - seen in the Ituri Forest and near Masongo (Zaîre); domatia inconspicuous (illustrated), being no more than a very slight swelling on the upper half or two-thirds of an internode when inhabited ants often had made a small circular opening just below the node. All ants observed were small Crematogaster; those identified were Crematogaster (Atopogyne) kohli (as Crem. africana ssp winkleri variety fickendeyi) - "a form commonly found nesting in other places". The ants had established regular colonies in the cavities with a queen, workers and brood, together with coccids fixed on the inner walls of the stem.

Randia species (p 461ff) - the main species found to be a myrmecophyte by Bequaert was Randia myrmecophyta. The ants he found were the small species Crematogaster (Sphaerocrema) rugosa. He noted, however, that Kohl (in Forel, 1916) had collected specimens of Camponotus foraminosus and Cataulacus weissi from its domatia. [In view of its size, I suspect that Camp. foraminosus, if correctly identified, is unlikely to have been resident in the domatia]. A related species, Randia physophylla, does not have swollen or even hollow stems. It does, howver, have expanded, or inflated leafbases and, near Leopoldville, Bequaert found some of these expansions to be pouch-like with a gland secreting a sweet substance. On some leaves specimens of Crematogaster (Atopogyne) laurenti (as an ssp of Crem. africana and as variety zeta) had taken possession of these distended nectaria, closing the opening with fibrous carton and often enclosing coccids; he noted also that they build tents over coccids on fruit.

Plectronia species (p 469ff) - three species appeared to be myrmecophytes. Plectronia connata has united bracts forming a sheath at the base of ramifications in the flower panicles and although he (apparently) saw no ants, local villagers called it "Boka na pombo" or "ant village". Plectronia glabrifolia was reported by earlier workers (Preuss and Schumann) as having ants living inside the hollow stem and probably also in the horizontal branches. Much more well documented was the species Plectronia laurentii. This is a shrub of some 2.25 m height with quadrangular stems showing opposite the leaves a groove pierced with openings which allow ants to enter the internodal cavity. It was discovered at various places along the banks of the Middle and Upper Congo and seems to be the main host of Crematogaster (Atopogyne) laurenti. Other species found in this plant were Crematogaster (Atopogyne) kohli (as winkleri ss and variety fickendeyi). Unidentified Plectronia also were inhabited by ants - Bequaert (p 474-6) denoted Plectronia species A, a climbing much branched bush - inhabited by Cataulacus weissi (as Cat. traegaordhi var plectroniae) and Technomyrmex kohli (as Engramma kohli). Plectronia species B, a creeper - with ants inhabiting a thickened main stem and branches, the ants found in the rain forest near Akavubi and Penge were a small unidentified Crematogaster. Plectronia species C, another creeper similar to B but with different shaped domatia, also had colnies of a small Crematogaster.

Cuviera species (p 477ff) - described as a strictly African genus, with fourteen described species, all but one possibly myrmecophytes and all known from within the Congo Basin (extending to the eastern mountains) and right across the West african forest zone. Most are shrubs or small trees. Those with ant species specifically mentioned are - Cuviera longiflora, with conical swellings on the basal internodes; the intenodes had two longitudinal rows of superposed orifices, often with a surrounding thickened ring, leading into a cavity containing small, black Crematogaster ants. Cuviera physinodes in which herbarium specimens were found to have nodal cavities with a few remains of ants. In the Congo Basin, Cuviera angolensis, a shrub to small tree with a trunk often bearing sharp spines; ants found in the [undescribed] domatia were "Crematogaster africana", Crematogaster (Atopogyne) laurenti (as ssp laurenti), with the coccid Stictococcus formicarius and Crematogaster (Atopogyne) kohli (as ssp winkleri). Bequaert (p 490) also noted six unnamed Cuviera species with ant inhabitants - plant collection No 1796 had Crematogaster species with complete colonies (there could be several separate colonies in one plant), Cataulacus pilosus, Axinidris hypoclinoides (as Technomymrex hypoclinoides) - these three species were all found colonising one plant); No 2461, with an unidentified Crematogaster; No 6429, with two ants, Axinidris denticulatum (as Engramma denticulatum) and Tetramorium meressei - Note Bolton (1980) found that the ant specimen was a distinctive species Tetramorium unicum; No ?, near Sitaweza, Crematogaster (Crematogaster) impressa (as Crem. excisa ssp andrei); No. ??, collected with Mr Lang, 8.iii.1915, along the Tshopo River, near Stanleyville, Crematogaster (Atopogyne) laurenti (as an ssp of Crem. africana and as variety zeta); No. 7983, plant with longer broader domatia, also reddish in colour, ants were Crematogaster (Crematogaster) impressiceps (variety frontalis)

Other domatia inhabiters

Bequaert (1922, p 407) gave a list of ants collected in the vicinity of Kisangani (Stanleyville) by Father Kohl "in myrmecophilous plants". These ants had been identified (or at least were listed by Forel (1916). These were -
Crematogaster ruspolii variety atriscapis (Forel). Now Crematogaster (Crematogaster) ruspolii.
Crematogaster (Crematogaster) sjostedti Mayr ssp kohliella Forel.
Crem. nigeriensis var wilniger (Forel). Now Crematogaster (Sphaerocrema) nigeriensis.
Crem. kasaiensis (Forel). Now Crematogaster (Atopogyne) kasaiensis.
Crem. kohli (Forel). Now Crematogaster (Atopogyne) kohli.
Crem. solenopsides ssp flavida var convexiclypea (Forel). Now Crematogaster (Decacrema) solenopsides.
Monomorium oscaris ssp springvalense var paternum Forel. Bolton (1987) recognised this as a full species Monomorium paternum, "known only from the holotype" from South Africa, collected by G. Arnold and described as the variety by Forel (1914). This poses the question, however, what were the specimens from Zaïre? Forel apparently (assuming Bequaert's quote was correct) thought the Kohl specimens were the same variety as those he had named from South Africa. Bolton's judgement makes this unlikely but Mon. springvalense Forel is a species from Zimbabwe. Presumably, one needs to look back to Monomorium oscaris as the likely species. The truth seems to be that oscaris, as recognised by Bolton (1987), is very variable and widespread across Africa and the "species" remains imperfectly understood. Mon. osacaris, moreover seems to be a savannah species and my own interpretation is that the specimens I saw and separated by earlier collectors as Monomorium species G, were of a rain forest. So what I list here under Mon. destructor seems more likely to be one of the facultative myrmecophytes.
Monomorium exiguum ssp flavescens Forel; simply regarded by Bolton (1987) as a junior synonym of Mon. exiguum.
Nesomyrmex evelynae Forel (formerly Leptothorax evelynae).
Tetramorium simillimum ssp isipingense var dumezi Forel. Raised to full species, Tetramorium dumezi by Bolton (1980). Tetram. isipingense, also raised to full species by Bolton (1980), was from South Africa. Bolton also seems to have misclaimed it as a new species erroneously overlooking the description by Menozzi (1942; cited in Bolton, 1995).
Engramma laurenti var congolense Forel; now regarded as Technomyrmex laurenti.
Prenolepis grisoni Forel; now recognised as Paratrechina grisoni.

Species identified by me from 2001 collections by Debout & Dalecky

Found in or on L. africana africana plants (single collections unless indicated).

In domatia -

Otherwise found on L. africana africana -

Other ants found in plant domatia or at extra-floral nectaries

© 2007, 2010 - Brian Taylor CBiol FSB FRES
11, Grazingfield, Wilford, Nottingham, NG11 7FN, U.K.