Camponotus olivieri

Camponotus olivieri is a widespread species in Africa, ranging from South Africa north to Sudan and west to Ghana. However, it is made up of a great many subspecies that probably deserve species status, so the situation may be rather more complicated than it seems at first.

Two subspecies of C. olivieri were collected in The Gambia: lemma and delagoensis. They differ quite markedly in pubescence and also, to a lesser extent, morphology. What I think provides some evidence that they deserve separate status is that they were both found at one site.

C. olivieri subsp. lemma was found in two locations: Abuko National Park, Lamin and Bijilo Forest Park, Kololi. In both cases it was found only on the ground. It can be distinguished from other species of C. olivieri by the rust colour at the base of the antennal scapes and the gaster, which is uniformly shiny, sparsely pubescent but still more densely pubescent than the mesosoma and has erect hairs that are thicker than the pubescence.

C. olivieri subsp. delagoensis was found at Abuko National Park, on a tree. It is similar to subsp. lemma, but has denser, yellow pubescence, especially on the gaster.

Both ants have been recorded only rarely, possibly due to the fact that they are regarded as subspecies and so have been more frequently recorded at species level. C. olivieri subsp. lemma had been recorded in Angola, Tanzania and former Zaire. C. olivieri subsp. delagoensis was only known from the type location at Delagoa Bay in Mozambique. This makes these Gambian records an extension of the known range of the species and both subspecies, especially large in the case of subsp. delagoensis.

These have both been compared with the type specimens from the Muséum d'histoire naturelle, Genève and the Naturhistorisches Museum Basel. This allowed me to confirm C. olivieri subsp. delagoenisis.

The syntypes of C. olivieri subsp. lemma are rather variably hairy, so much so that I wondered if Forel had mounted specimens from different colonies on the same pins. The main difference between these and my specimens was that most of the types were much less hairy, though one was similar to mine. It could be that the specimens have lost some of their pilosity. Regardless, I feel I need to do some more work to confirm that there is nothing closer.

Plagiolepis mediorufa

Plagiolepis mediorufa had only been recorded from the Congo and the Central African Republic, generally from myrmecophilous plants. My Gambian specimens were collected from plants, trees and a palm frond in Bijilo Forest Park, Kololi and Abuko National Park, Lamin, but nothing about the plants indicated that they were adapted to supporting ants. The Gambia also represents a significant range extension north and westwards.

The trouble is that I suspect there may be a few, as yet undescribed, small yellow and morphologically similar species of Plagiolepis in Africa as a whole. I have placed my specimens in P. mediorufa because it is currently the best fit, but would be interested to see where they are placed if the genus is ever reviewed.

The specimen that I photographed was sadly rather battered. Plagiolepis often tend to be rather soft and fragile, and so shrivel when they dry. Tapinoma does the same thing. (I think the funiculus of the antenna was missing when I collected it.) It was still the best of the three specimens that I had mounted.

Slightly confused Monomorium egens

This specimen has proved difficult to identify, but I'm now pretty certain that I've got it right. It keys out pretty clearly as Monomorium egens using Bolton (1987), but is generally much more slender than the species that Bolton describes and has much longer scapes (SI 108).

Because it doesn't fit perfectly I've been puzzling over it for the past couple days. The resolution came when I translated Santschi's (1926) description of M. longiusculum from the French. This describes a slender species with scapes long enough to reach the posterior margin of the head (I've included my rough translation of Santschi's description below). This means that my specimen has slightly longer antennal scapes and may be more slender, but is probably close enough.

Bolton synonomised M. longiusculum with M. egens. What is strange is that he doesn't mention this level of variety despite having examined the type material for M. longiusculum, though he does confess not to be convinced that M. egens is a single species. Having now compared my specimens with those checked by Bolton in the Natural History Museum, London, I can understand why he decided to synonymise them, as there is no obvious difference other than the shape.

This species is another forest species from Abuko National Park in The Gambia, where it was collected from a tree. Bolton states that M. egens nests in rotten wood in the soil or in fallen trunks and forages in the wood and leaf litter. This seems to make finding it part way up a living tree trunk quite usual.

M. egens has been found in West Africa from Angola to Guinea, putting this specimen at the extreme northern edge of its known range.

The following is my translation (with a little help from Brian Taylor) of the type description for M. longiusculum from the French.

Monomoriumlongiusculum Santschi 1926

Worker. Length: 2.1 mm. Body brown, gaster brown-black. Appendages yellowish-brown. Funiculus yellowish. Smooth, shining. Slightly pilous. Pubescence suberect and more abundant on the scapes, adpressed and sparse on the legs.

Head approximately a quarter longer than broad, rather convex at the sides, the posterior margin straight with the angles rounded. Eyes two thirds as large as the space which separates them from the anterior margin of the head and placed between the middle and a third back from the anterior margin. Carina on the clypeus marked, not very divergent and little or not projecting at the anterior margin. Mandibles with 4 teeth. The scape reaches the posterior margin of the head. Articles 2 to 9 of the funiculus about as thick as long. Pronotum 'sub-shouldered', without a promesonotal suture and with the mesonotum in profile forming a regular and rather low convexity from the anterior to the metanotal groove. Propodeum longer than two thirds of the promesonotum and low, also convex, the sloping face not very distinct from the declivitous one; convex from one side to the other and narrow, width about half its length. Peduncle of the petiole as long as half of the base of the node; node triangular in profile and longer than high, not convex ventrally. Postpetiole a little shorter and lower than the petiole, roughly as high as long and rounded at the dorsally, as broad as long and a little broader than the petiole.

Cataulacus traegaordhi

This is the second Cataulacus collected from Abuko National Park in The Gambia (the other one was C. guineensis). I only managed to find one specimen of C. traegaordhi, so either it's less conspicuous, rarer or I just wasn't looking in the right places.

It has been found from South Africa north to Sudan, but apparently the closest it has been found to The Gambia is Ghana. Whilst finding C. guineensis in The Gambia apparently represented an northward extension of its known range, finding C. traegaordhi appears to have extended its known range westward.

Cataulacus guineensis

At the risk of unintentionally starting a theme that could potentially be very restricting and uninteresting, I think I'm going to continue to post 'ant portraits'. Someone might actually find them useful.

This one is Cataulacus guineensis. It was collected Abuko National Park, one of the more famous protected areas in The Gambia. Abuko is a remnant of gallery forest, rather than rainforest. Despite its small size and the fact that we hired a guide (which for me meant that I didn't really have enough time to stop and collect ants), I still managed to pick up some species of interest.

Three of these, C. guineensis, Cataulacus traegaordhi and Pyramica maynei are proper forest species, so finding them in one of the few remaining pieces of proper forest in The Gambia was quite satisfying.

C. guineensis has been found in the Republic of Guinea, as might be expected from its name, and throughout west Africa, but not from Senegal or further north, so this find from The Gambia may represent the northern limits of its known range.