New year, new home, new job, new species

Apologies for the lack of recent posts. I moved at the end of November to start a new job in Talgarth, Wales. Following my move it took my ISP a whole month to set up my connection here, with a lot of extended phone calls and a rather long and comprehensive written complaint from me to get them to sort it out as quick as they did. Needless to say I am not best pleased with the company.

One rather important event that took place over the last month was that my recent paper was published, describing a new species, Monomorium subcomae. It may not be much, but it is my first new species. (I don't have the time or resources to conduct large scale taxonomic reviews. At the time I did the M. subcomae work I was working off of a table in my kitchen - at least now I have a dedicated office/lab.)

The type material for M. subcomae was collected in Kuwait by David M. King, though Mostafa Sharaf has already informed me that he has the species from Egypt. The specimens gradually found their way to me through Brian Taylor, along with numerous other tubes from around the Mediterranean.

M. subcomae is one of many species in the Middle East and North Africa that are related to Monomorium areniphilum, all of which have a propodeum that it on a distinctly lower plane than the promesonotum, as well as large eyes and distinctive striate sculpture on the head. Not many of the areniphilum-complex are bicoloured, so this makes M. subcomae relatively easy to identify. The key in Collingwood & Agosti (1996) can be easily adapted to include M. subcomae as follows:

17	Eyes large, greater than 0.25 times HW		17a
	Eyes small, 0.25 times HW or less		18
17a	Ventral surface of head with numerous long setae		subcomae
	Ventral surface of head glabrous		venustum

As yet nothing is known about the ecology of M. subcomae. Perhaps over time people like Mostafa will be able to fill in some of the details.


Citation and abstract: Lush, M. J. 2008. A new species of Monomorium (Hymenoptera: Formicidae) from Kuwait. Zoology in the Middle East 45: 67-72.

Monomorium dakarense

I previously thought I had collected Monomorium dictator in the Gambia, as that is what this specimen keyed out as. However, I've been doing a lot of work on the salomonis-group recently and I no longer think that I was correct. I now think it is Monomorium dakarense.

It all boils down to couplet 36 of Bolton's (1987) key. I think it would be possible to debate for hours over whether the sculpture on the head of this specimen is 'uniformly densely reticulate-punctate' or 'with a silky, smeared or roughened appearance'. Initially I opted for the former because, well, it is reticulate-punctate, just more finely than the likes of Monomorium bicolor! However, I've since come to realise that this is what Bolton means by the latter, which leads to M. dakarense.

The difference between M. dakarense and M. dictator, other than the ambiguities of cephalic sculpture, seems to be size, number of ommatidia in the longest row and, importantly, scape index (SI). M. dakarense is overall the smaller of the two, with fewer ommatidia and a SI of 95-100, whereas M. dictator has a SI of 107-109. For those not familiar with SI, it is as follows:

Scape length × 100

Head width

The SI in this specimen is 92, putting it closest to the range given for M. dakarense. Given that Bolton only had the three syntype workers to measure it is likely that the true range of the SI includes 92. However, this is not the only difference between this specimen and the holotype, as the other measurements are (quoting the measurements for MJL143, followed by the range given by Bolton, in mm):

     Head length = 0.61 (0.57-0.59)
     Head width = 0.51 (0.44-0.47)
     Cephalic index (ratio of head width to height) = 84 (77-80)
     Scape length = 0.47 (0.44-0.45)
     Pronotal width = 0.31 (0.30-0.31)
     Mesosoma length = 0.72 (0.66-0.70)

Despite the larger size, the specimen is not big enough to be M. dictator and differs in the other features mentioned, so it is most likely M. dakarense.

It still remains a bit of a rediscovery. M. dakarense had been collected once in Senegal in 1914, so it's more likely than M. dictator, which had only been collected in Angola. The only specimens that I collected were found on the ground at Madiyana Camp on Jinack Island, and only at night. Since we stayed at Madiyana Camp for a few days it would be surprising if M. dakarense had been active during the day and I had not collected it then, which indicates pretty strongly that it is entirely nocturnal. Perhaps a combination of its nocturnal habits and its small size have meant that it has not been found again until now?

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.

Corrections

Before I disappeared for Easter I visited the London Natural History Museum to compare my some of my Gambian specimens with ant specimens in their collection. As a result, I have a few changes to make, but need to do a bit more work before I make them. Until I change the posts, this will hopefully caution against relying on previous posts.

I had misidentified the following species:

• Camponotus cosmicus - more likely within what can best be described as the vestitus complex.
• Monomorium dolatu - doesn't appear to be any of the species included in Bolton (1987). I had suspected that this was the case, but without checking reference material went with the closest option.

I had correctly identified these species:

• Monomorium exiguum
• M. rosae
• M. osiridis
• M. vonatu
• M. egens
• Dorylus affinis

These species are perhaps open to debate, as I couldn't conclusively establish whether they were the same species or different:

• Camponotus rufoglaucus controversus - slight differences in setae and pubescence but the specimens checked were not types and were majors only.
• Camponotus olivieri lemma and delagoensis - I couldn't check these subspecies.
• Crematogaster impressa - the specimens present were collected by Donisthorpe and did not appear to be the same as mine or each other. Chances are this species and C. excisa will not be resolved until the taxonomy is revised.

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.

Monomorium osiridis

Monomorium osiridis had only been collected twice, in Kenya, before I picked up these specimens in The Gambia. It seems quite surprising to find M. osiridis on the other side of the continent, but I don't know what else these specimens could be.

M. osiridis and the southern African species Monomorium zulu and Monomorium rabirium are separated from other Monomorium by having 12-segmented antennae, smooth mandibles, conspicuous eyes, sculptured propodeum and no standing hairs on the dorsal mesosoma and gaster. M. osiridis differs from the other two by having a sculptured head, except for a median strip (visible in the bottom photograph).

I only collected M. osiridis once, on the ground at Madiyana Camp on Jinack Island. They were collected only at night, strongly indicating that they are entirely nocturnal, as may be the case with Monomorium dictator. This could be another instance of a species being under-recorded partly because it is nocturnal.

These have been compared with specimens checked by Bolton at the Natural History Museum, London, and are confirmed as M. osiridis.

Monomorium rosae

Monomorium rosae is a widely distributed species with a central African distribution that stretches from Kenya to Senegal. It was collected twice on Jinack Island in The Gambia, once on a tree and once in dry leaf litter at the base of a tree.

Bolton (1987) notes that this species varies in size and pilosity over its range, suggesting that M. rosae may contain more than one species. He distinguishes the species as currently defined as having 11-segmented antennae, dark colour, moderately long scapes and a distinctively shaped postpetiole.

It's interesting how many of the Monomorium now known from The Gambia have 11-segmented antennae. M. dolatu, M. exiguum, M. mictilis and M. rosae all have 11-segmented antennae, out of ten species recorded from The Gambia (40%). This contrasts with 12 species out of 149 listed by Bolton for Africa as a whole (8%). Maybe Monomorium with 11-segmented antennae are more common in this part of west Africa?

These have been compared with specimens checked by Bolton at the Natural History Museum, London, and are confirmed as M. rosae.

Extreme myrmecology: Monomorium mictile

Monomorium mictile has to be the smallest ant I have ever found. It is very inconspicuous.

I started off with four specimens, but misplaced two before I could look at them properly (I still don't know how). I selected one of the two specimens to be mounted and, whilst I was getting everything ready, I brushed a bit of dust off my microscope stage. I knew what I had done as soon as I had done it - the bit of dust was the ant. It was no good looking for it on the floor, as it was gone.

This left me with just one, which had not died in a position that was conducive to mounting and I felt that trying to fix this would be too risky on such a small specimen. This is why the specimen in the photograph is not as well mounted as most others.

Bolton (1987) comments that material of this species is relatively scarce; it's not hard to see why!

M. mictile is widespread in Africa, found from South Africa north to Mali and Sudan. It as collected once in The Gambia from a tree in the coastal scrub on Jinack Island.

Monomorium exiguum

Monomorium exiguum has been found across central and southern Africa, from Ethiopia in the east to Guinea in the west and Zimbabwe in the south. It appears to be primarily a forest species, so it is no surprise that the Gambian specimens were collected from a tree in Abuko National Park, one of the few remaining patches of gallery forest.

Bolton (1987) states that M. exiguum as defined definitely contains more than one valid species, but could not resolve them. It is therefore interesting to note the small size of the Gambian specimens, which are apparently much smaller than is typical for the species; Bolton gives lengths of 1.5-1.7 mm whereas the Gambian specimens can be little more than 1 mm long.

These have been compared with specimens checked by Bolton at the Natural History Museum, London, and are confirmed as M. exiguum.

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.

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.

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.