Monomorium sp. A

When I first attempted to identify this ant I decided that it was Monomorium exiguum, though I wasn't exactly convinced. I was using Bolton (1987), though I find the key fairly vague at times, which isn't helped by the fact that the descriptions aren't exactly consistent and many species lack diagrams.

M. exiguum is the last species in the key - okay, so there aren't that many Afrotropical Monomorium with 11 antennal segments, but even so I feel that if you've got to the end of the key and your not convinced, then chances are you are wrong.

Then I discovered that I had collected specimens that were a perfect match for M. exiguum and very different from this species, so it was clear that I was wrong. I went back to the key and decided that the next best fit was Monomorium dolatu, though I was rather less than convinced - the petiole shape and Cephalic Index appeared to be correct, but there were slight differences in the structure of the clypeus.

My trip to the Natural History Museum, London has thrown the latest spanner in the works, as I've now been able to examine specimens that Bolton identified as M. dolatu closely. It's pretty clear that this isn't M. dolatu, as the petiole shape is not near as conical as on that species and it's generally wrong. I was also able to check and eliminate M. pulchrum, M. taedium, M. fastidium and M. vaguum. I have in my collection and was able to confirm M. rosae, M. exiguum and M. mictilis. The only other species that it could remotely be is M. bequaerti, which was not present in the museum collection, but this should have a postpetiole the same size as the petiole, as in M. pulchrum, which my specimen does not have.

Since I've eliminated all Afrotropical species of Monomorium with 11 antennal segments I'm having to call it 'species A' for the moment, at least until I've checked those species occurring elsewhere. This is the second potentially new species of Monomorium I've encountered in as many months - the first I've already established is definitely new.

M. sp. A was collected once, nesting within an Acacia pod, in Kololi. Because this was within our last few hours in Gambia and I had packed everything to leave, they were collected alive. I had to carry the pod, with the ants, back to the hotel in my hand. This involved dodging the bumsters (notorious in The Gambia) and trying to keep the pod safe whilst I had a chat with a charming young Gambian woman, who invited me to a 'club' and I suspected to be a prostitute. Once I made it back to my room I put the pod and the ants in a bag and in my case, where they remained until I got home.

I kept them alive for a few days before realising all I had were a few workers - not worth the effort of keeping long-term. They were also a pain; they proved to have an incredible ability to walk upside down on a smooth surface and vertically across fluon. This, combined with the fact that they tended to wedge themselves into the small gap between container and lid made them very difficult to contain. Given these recorded habits it seems that this species is well adapted to an arboreal lifestyle.

Incidentally, the droplets of liquid are grease. I will have to do something about this soon, whereupon I may upload some fresh photographs.

Camponotus vestitus subsp. intuens

I originally identified this as Camponotus cosmicus and wrote a nice long blog defending my decision to call it that. I even provisionally synonomised it with a few other species and subspecies. I was wrong!

At the time, I sent photographs to Brian Taylor, who replied, 'Why do you not think this is Camponotus vestitus?' Perhaps I should have recognised that his far greater experience was likely to lead to a correct identification, but I like to learn from my own mistakes.

C. cosmicus was one of the species that I checked when I visited the London Natural History Museum, as the holotype is there. C. cosmicus is a large and fairly stocky ant, even the minors, unlike my specimens. I was also able to check C. vestitus subsp. pectitus, which has all the right features (divergent pubescence on the gaster, same number of setae on the mesosoma, same propodeum shape) and differs only slightly in the colour of the head.

Arnold (1924) stated that Smith's (1858) description of C. cosmicus is useless, and it appears as though he is right. However, none of the authors who have written about C. cosmicus picked up on what I believe is probably the most significant characteristic, as all specimens in the museum had many erect setae on the ventral surface of the head. I can also add that C. cosmicus is predominantly very dark red (not black), with the propodeum rounding smoothly from the metanotal groove, less divergent pubescence on the gaster and a greater number of setae on the mesosoma.

So, maybe it is C. vestitus subsp. pectitus. It gets complicated because Bolton (1995) states that Santschi (1926) suggested that C. vestitus subsp. pectitus and C. vestitus subsp. intuens are the same, but at no point do they appear to have been properly synonymised. Reading Santschi's statement, it seems pretty clear that he has no doubt, so I can only assume that Bolton did not synonymise it because the description of C. vestitus subsp. pectitus post dates this statement! Forel's (1909) description of C. vestitus subsp. intuens is just as ambiguous as the descriptions of C. cosmicus and C. vestitus subsp. pectitus.

Update Nov 2008: My specimens have now been compared with the type specimens from the Naturhistorisches Museum Basel. This allowed me to confirm that they are very clearly C. vestitus subsp. intuens - a completely identical match. Possibly the colour of the head is the key feature in discriminating these subspecies.

I also showed my specimens to Cedric Collingwood, who claimed them to be C. jizani. This is a species from the Middle East, though he admitted that the only reason he named it thus was because he didn't know what else to call it! Possibly, C. jizani is a junior synonym of C. vestitus subsp. intuens or C. vestitus.

This species was collected a number of times only in the grounds of the hotel we were staying at in Kololi, Gambia. Here it could be found nesting in turret nests, so named because there were steep 'craters' of sand piled around the nest entrances, up to about an inch high. These are described by Arnold (op. cit.) for C. vestitus subsp. pectitus, which he states is rare and found nesting in sandy soils. He then describes,

'nest-entrances[s] surrounded by a circular, high and sharp-edged crater... This form of crater is distinctive of this insect.'

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.

Monomorium bicolor

Monomorium bicolor is an abundant ant in The Gambia. It had been collected there before in around 1926 in Banjul (formerly Bathurst), and in 2007 in Kololi and on Jinack Island. It is distributed from Angola north to Sudan and from Somalia across to Senegal.

M. bicolor seems to be present in a variety of habitats, as it was found on trees, on the ground in open areas, on buildings and once scavenging from a dead fish, but was only found nesting in the ground.

M. bicolor is very similar to Monomorium dictator, but differs by being generally larger, though also variable in size, and lacking abundant setae on the anterior half of the first gastral tergite. It should have at least two erect setae on the anterior margin of the first gastral tergite, but these were lacking in all Gambian specimens. Five out of the nine specimens examined had distinct pits where the setae should have been, but all lacked setae. Nevertheless, there is no doubt that they are M. bicolor, so the hairs have perhaps rubbed off or Bolton (1987) defined the species too narrowly.

Cataglyphis oasium

The size of an ant and how easy it is to identify are not necessarily related. Whilst Monomorium mictile, at just over 1 mm, was relatively easy to identify, I'd been pondering this very large species of Cataglyphis for weeks.

Cataglyphis is a genus that is taxonomically muddled. I've finally concluded that this species is probably Cataglyphis oasium. It was the keys in Santschi (1929) and Radchenko (1998) that eventually provided the most likely identification.

C. oasium was originally described by Santschi (1929), though the name he gave it (Cataglyphis bicolor st. nodus v. oasium) was invalid, so the authority for this species is Menozzi, 1932. Menozzi only gave two lines of text to the species, changing the name to Cataglyphis bicolor var. oasium, without noting that it was a new combination or providing a fresh description, and naming Santschi as the authority. The variety oasium was later given subspecies status and then species status by Radchenko (1997). Wehner, Wehner & Agosti (1994) suggested that C. bicolor subsp. oasium was synonymous with Cataglyphis savignyi, though they didn't actually synonomise the two names. Thus, the valid name is C. oasium. It's very confusing, so it took a little while just to sort out this history.

Information on the distribution of C. oasium is very sparse. Santschi mentions records from Tunisia and Algeria, whilst the most recent record that I'm aware of is Libya in 1931, which is reported by Menozzi. Radchenko (1998) states that it is found in North Africa and the Middle East.

This gives the impression that C. oasium is rare, but this seems unlikely. It is probably under-recorded due to the taxonomic difficulties. It is possible that the species collected by Lenoir and mentioned in The Ants of Africa is also this species. If C. oasium is found in oasis in the Sahara and in the Middle East it seems reasonable that it could also occur in The Gambia and Burkina Faso.

The Gambian specimens were collected from Kololi and Madiyana Camp on Jinack Island, mainly from sandy ground in scrub savannah. In this sort of hot scrub savannah it could be quite common, so it may be abundant further inland, away from the coastal breeze.

Monomorium vonatu

Yet another rediscovery. It gets too familiar after a while, but it does demonstrate how little is known about the ants of Africa.

Monomorium vonatu was known only from a single holotype specimen in the Natural History Museum, London. It was collected in 1970 in Ghana and described by Bolton (1987). It is easily distinguished from other species of Monomorium by the shape of the petiole and postpetiole, which both have distinct ridges running across them. The only other species that has this structure is Monomorium mirandum, which is very distinctly bicoloured.

As if to demonstrate that you don't need to go to great lengths to find interesting species, I collected my M. vonatu specimens in the grounds of the hotel we were staying in. They were found on the ground, either in bare sand or grassy areas.

Quite why this species hasn't been discovered anywhere else seems a bit of a mystery, as it was probably pretty common in suburban Kololi. Perhaps it is overlooked as another small black species of Monomorium.

These have been compared the holotype at the Natural History Museum, London, and are confirmed as M. vonatu.

Monomorium afrum

Monomorium afrum is the largest species in its genus found in the Gambia so far. It is very widespread in Africa, being from from South Africa to Sudan. The closest it has been found to The Gambia is the Ivory Coast, so this find represents an extension of its known range westwards.

It was found only once as a worker, running on the ground in the coastal resort of Kololi. Other species of Monomorium are much more common in The Gambia.

The sculpturation of the head and mesosoma is interesting, as it makes even in focus pictures appear out of focus. This reticulate-punctate sculpturation can be seen on the close up photograph of the head.

On the same day and in the same location as the M. afrum worker was found I collected a lone dealate queen. Queens away from colonies present problems for identification, as most have not been described. For this reason, I left the Monomorium queens that I collected until last (within the Monomorium at least). Fortunately, the queen of M. afrum has been described by Arnold (1926).

What's more, it is incredibly distinctive. In fact, when I first looked at it, I assumed that it was a Tetramorium, at least until I realised that it had the single unpaired seta projecting from the midpoint of the anterior clypeus typical of Monomorium and lacked the raised clypeal ridges of Tetramorium. It is the most peculiar Monomoroium that I have ever encountered.

My specimen seems to differ slightly from those described by Arnold. He describes the second and third abdominal segments of M. afrum queens being anteriorly smooth and shining. This presents a problem, as the second and third abdominal segment is the petiole and postpetiole. However, authors are sometimes unclear about this, so Arnold could have been referring to the second and third gastral segments (abdominal segments five and six). Despite this uncertainty, I can find no smooth and shining areas on any part of my specimen.

The queen of M. afrum is obviously very different from the worker. Arnold states that had he collected a specimen without the context of workers and other queens he would have considered it to be the type of an entirely new genus, and it's easy to understand why. Bolton (1987) comments that it shows modifications characteristic of socially parasitic species of Monomorium and may prove to be a temporary social parasite.

Tetramorium sericeiventre

Tetramorium sericeiventre is a very widespread species, occurring from South Africa north to Mali. A single worker had been collected in The Gambia in 1926, recorded as subsp. arenarium.

This species is not as common as some ants in The Gambia, but can be found in Kololi and on Jinack Island, where it can be quite conspicuous. It was collected from savannah, where it nested in the ground.

I was lucky enough to retrieve a queen from one of the nests, which is shown in one of the photographs.