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.

Tropical plants at the Eden Project

When the development of the Eden Project first started in Cornwall I made a prediction: that their biomes would become overrun with ants. This wasn't completely without precedent, as the this is exactly what had happened with Biosphere 2 with the crazy ant Paratrechina longicornis.

I'm rarely this accurate, so I'm feeling quite smug!

My first encounter with ants from the Eden Project was having a specimen thrust in front of me by Cedric Collingwood a few years ago. His explanation was that it had been brought to him by a friend who couldn't initially remember where he collected it, but quickly remembered when it became apparent that it was a tropical species. Since I hadn't encountered the species before I quickly forgot what it was.

Last year one of my colleagues brought me a specimen that he had collected from the tropical biome at the Eden Project (I like colleagues that bring me ants). This was clearly a Technomyrmex, probably T. albipes, but I really struggled to come to a satisfactory conclusion on which species it was, so made a note to visit the Eden Project to collect some more and hopefully make identification easier. I did this last Friday.

Within seconds of entering the tropical biome I had found ants. The biome is absolutely full of them. In one place they were so dense that with one puff on my pooter I collected about 40 specimens! Unfortunately, I only found one species: Technomyrmex. With the number that I collected I should be able to make a better species identification.

I've since had a chat with the person who deals with pest control at the Eden Project, Michael Pytel. He stated that they are T. albipes (I'm still going to check) and that they had actually declined in numbers over the past two years! Apparently they were not the only ant to have been introduced and actually displaced P. longicornis, the species that caused problems at Biosphere 2. Other ants that still occur include subterranean Pheidole and Hypoponera, and a species of Solenopsis has been found there in the past. Work will continue to try to reduce the Technomyrmex population and redress the balance.

T. abipes is a major pest species in the tropics. It would be easy to consider Technomyrmex only as a pest in the tropical biome, but I think it deserves a little more respect. Even if it escapes the biome it is very unlikely that it would become established, as the climate in the UK is too cold. It is probably the only contact with such a prominent tropical invertebrate that visitors to the Eden Project are likely to come across and so could be a valuable educational tool. They could demonstrate the global problem with species occurring in the wrong environment and the damage that they can cause to ecosystems. I'd like to see the Eden Project recognise this opportunity, if they have not already.

(Apologies to anyone who actually expected this to be about tropical plants!)

A froggy reprieve

It happens rarely. Every so often something happens that provides a glimmer of optimism for the conservation ecologist. This is probably one of those events.

I spotted the story a few days ago on the BBC News pages, but typically it took me a while to react. Apparently a team of researchers from the University of Otago have discovered a possible cure to chytridiomycosis in frogs. Frogs have been suffering serious declines worldwide due to a mystery disease and chytridiomycosis is one of the candidates for the cause. The researchers used chloramphenicol to cure animals of the disease in the lab.

Sadly, chloramphenicol has health implications in humans, so is unlikely to be used in a wider context. However it is very valuable progress. With continued research on this and other possibilities it might be possible to halt the decline and extinction of frogs and other amphibians.

Pachycondyla sennaarensis

Pachycondyla sennaarensis is probably one of the most common ant species in the coastal region of The Gambia, as I collected it 10 times. I also got to know it over the week that I was there and had soon started to ignore the many lone workers that I frequently saw.

Remarkably, given how common it is in the area that other myrmecologists were most likely to visit, it hadn't been recorded from The Gambia before. I'd be tempted to suggest that it might have spread into the country since the early 20th century, when the last myrmecologists visited, but it was recorded in Senegal at about that time. Perhaps it's just been more successful than other ants as the area has been developed.

It seemed equally happy around buildings and in natural areas, where it nested directly in the ground, often in cracks in concrete. It was described by Dejean & Lachaud (1994) as being at least partially seed eating, which is extremely unusual for a ponerine ant. My observations agree with this, as the refuse piles around nest entrances often contained seed husks and other vegetable matter.

They also showed the kind of wear on their teeth that other seed eaters, such as Messor, tend to develop on older workers. Rather typically, it proved impossible to get a decent photograph of the one specimen that showed really distinctive wear. I hope that the photos below give some indication of what I mean, despite the fact that they both chose to die chewing on their own legs.

The first one shows little wear:

Whilst the second shows slightly more (note particularly the tooth on the right just above the leg):

Perhaps you'll just have to take my word for it.

I also found a queen. This was washed up on the shore on the part of Jinack Island that is within Senegal, though it probably washed down the river Gambia to get there, as it was already dead. Despite the fact that it was not found in a colony, it has been possible to identify it as P. sennaarensis with some confidence, as none of the defining features are on the mesosoma and so are presumably the same on the queen as the worker.

This species also stings. I discovered this on my first day in The Gambia when, in my rush to get out and explore, I left my forceps and pooter in my case in the hotel. Picking up these with your fingers is perhaps not to be recommended! In terms pain, it wasn't actually too bad initially (I've been stung by worse), perhaps rating as a 2.5 on the Schmitt Sting Pain Index (just above a European honey bee). However, after 20 or so my thumb, in particular, was starting to feel a bit numb, so I decided to stop. For the next 3 days the skin on my thumb and forefinger, which had taken the bulk of the punishment, slowly peeled away.

All good fun.

Nesomyrmex angulatus

Nesomyrmex angulatus is another widespread species, found from South Africa to Saudi Arabia. The closest it has previously been found to The Gambia is Ghana, so this represents another western range extension (along with Cataulacus traegaordhi). The key thing about this species that separates it from other Nesomyrmex is the very smooth profile of the mesosoma, coupled with the yellow colour.

Though I only found it twice, it's probably fairly common in more wooded parts of The Gambia. It tends to be pretty inconspicuous. I collected it from trees in Bijilo Forest Park and on Jinack Island, from coastal forest and scrub savannah respectively.

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.

Harmonia is overrated

Earlier this week I was in Dover, Kent and encountered my first harlequin ladybirds, Harmonia axyridis.

The surprising thing was that I hadn't already seen any. Since it first appeared in the UK in 2004 the species has spread at an incredible rate, and is now known from much of England and parts of Wales.

Because they are an invasive species that threaten the ladybirds native to the UK I collected as many as I could. On Thursday I took these into work not far from Bristol to show my colleagues what they should be looking out for, feeling a little smug that I could do this, until one of the people I work with, Jenna, mentioned that there were some in the window that were the same. She was absolutely right, they were harlequins as well.

As a result I scoured the office building, removing as many as I could find. This resulted in 28, to which I added a further 14 yesterday (Friday).

The question I guess I should ask myself, as an entomologist, is how did I miss these? The simple answer is complacency - I assumed that if they were in the area they would be pretty rare. Despite this I don't think we had any here last year, except perhaps for the odd one or two, so the speed at which they've become established is staggering.

I will continue to remove the ones that I find, but I think it's a lost cause. I think they're probably here to stay.

Sightings of the harlequin ladybird are being collected by the Harlequin Ladybird Survey, and can be submitted online.