Antroducing: the tiny ninja-ants of the Danube delta (Cardiocondyla elegans)

As Kittenmancer and I went on our two-week holiday to Romania, surprisingly, finding new ants wasn't that big of a priority. We left our fancy new macro lens home and, as we figured our trip would be too late in the season for nuptial flights, the ant-hunting kit consisted of merely a few catch tubes. In a stroke of bad luck, the flight company forgot to put my backpack on the airplane, so we didn't even have those as we headed towards our destination for the first week: the Danube Delta at the Black Sea. 

However, as we travelled we noticed that the Romanian ants, like Tetramorium and Formica species, with a sunny thirty degrees Celsius, were still very much active. Usually I would try to catch a single worker to be folded into paper napkins for later study, but sometimes this proved quite a challenge. Like for instance the Formica rufibarbis we found swarming over a big pile of chopped firewood laid out to dry - these big ants were easy enough to spot, but surprisingly hard to catch. Warmed up in the full sun, they are insanely fast and have pretty good eyesight for an ant to boot. However, being really small can make an ant even harder to pin down with a scrap of paper...

While waiting for the ferry that would bring us to Sfantu Gheorghe, we sat down in the yard of some abandoned factory that bordered the dock. With all the pavement tiles under our feet it was no surprise to find the 'Pavement Ant' here: Tetramorium caespitum. Something was weird though: they seemed to come in two sizes! While a lot of ant species have castes of differently sized (and sometimes shaped) workers, this one does not. And while typically the first worker generation of a new queen can be a lot smaller than normal, mature colonies lack these 'nanitics'. Was it a different species then? But they looked so much alike and Tetramorium ants are notoriously bad neighbours.

That's one tiny ant. Too bad I couldn't take this picture until we got home.

So I whipped out my Pok├ęball tissues in an attempt to catch one of these tiny workers. Problem though: these workers were not just 'tiny', they were downright miniscule! And they moved in a careful and meticulous manner, rarely leaving the safety of the cracks between the pavement tiles. When agitated, they didn't run around erratically like most ants would, but instead they just stopped under the closest cover and disappeared. Finally I did manage to scoop one onto a piece of paper, only to have it escape effortlessly between the folds and jump to freedom. Of course by then the ferry was arriving...

The next day, first thing, we went to visit the beach taking a path next to the river that would lead us to the dune area. And here, right in the middle of the track on this well-throdden dirt road we found our tiny ninjas again, and here also with Tetramorium running everywhere. But now it was clear that these were separate species, because we could clearly spot the tiny ants only using their own tiny-sized entrances to their underground nest. We also now witnessed how they manage to have their nest right next to a species that engages in full-scale warfare as a hobby: our tiny ants are masters of genjutsu, the ninja-art of illusion!

Whenever we saw a big ant run into a tiny ant, the latter would immediately flatten down and hold still, as if pretending to be a few grains of sand. And then the big ant would just walk past or sometimes even over these few grains of very uninteresting sand. So what's the ninja's secret? Probably pheromones, either copied or some sort of masking agent. Sure, these ants are tiny, but being half the size of a Tetramorium worker should still get an insect noticed and killed. However, most ants use only their sense of smell to identify friends, foes and dinner: a security system that many of the microcosmos have evolved hacks and exploits for.

At that point I was getting quite fascinated by the tiny ants, quite certain that this was not a species that could be found in the Netherlands. Kittenmancer and I poked a bit at the entrance of the nest, but the caked clay proved hard as rock. We did find something that looked like a very small wasp walking on the path close to the nest. However the fact that her miniscule antennae had an 'elbow' bent to them meant it had to be an ant queen instead. Did she belong to the tiny ninjas? But why was she still walking outside and hadn't she shedded her wings yet? Had she overslept for her mating flight? We decided to take her along anyway in a little plastic cup we had scrounged.

Can you spot the right rock?

As we proceeded further towards the beach we flipped the occasional rock to see what was under them, until suddenly we hit the jackpot! Under a square piece of rubble at the entrance of a small dried-out pasture, just before surrounding area turns into sandy dunes, we uncover a big brood chamber of a colony of our ninja ants. Quickly we scoop pupae, larvae and workers into our second and last plastic cup. Merely a tablespoon, but with ants this size that meant we had hundreds of them, but no queens, nor eggs so far as we could see.

Realizing that, with this rather knee-jerk reaction, we are now committed to getting a colony of this unknown species, we needed to get serious about this and acquire additional supplies. After having spent some time on the beach (and having encountered other fascinating ant species in the dunes) we raise some eyebrows at the local store when we buy spoons, paint brushes and plastic boxes, and we borrow a proper spade from our host.

However, even with the spade we have a hard time digging in the hard clay, having to fight rocks for every centimeter. Under the uninterested stares of some local cows and curious looks of  beach-goers passing by, we slowly but steadily created a respectable hole, yet still no queen. We figure the nest must be larger than we can feasibly dig in this ground and are close to giving up until I take one last good look at our tailings. I notice that several of the ants running around there are slightly bigger than the rest... wait a minute, those are the queens!? Realizing we foolishly had been looking for a queen of a much larger size (and having totally forgotten about the tiny winged queen we had caught before), we quickly went from zero queens to half a dozen.

First we housed them in a cheap plastic box, in which they would dig out tunnels and rooms in even a few milimeters or dirt. This was definitely temporary as the whole next would collapse every time we had to open the lid. Next top was a glass jar with some moistened cotton and a few crumpled sheets of toiletpaper for them to hide in the folds. This proved troublesome as well, as the toiletpaper quickly started moulding and many of the freshly eclosed workers were drowning in the condensation on the glass (the older workers recognize this danger and, if possible, pile up dirt on everything wet, even their food).

It wasn't until we returned to Bucharest for the start second part of our trip that we were able to relocate the colony to a proper test tube scrounged by Kittenmancer's parents. As we moved all the brood and workers to their new temporary home, peeling brood and workers even from within the 3-ply toilet paper itself (they could hide everywhere), we also found that we actually had at least 3 more queens than we originally thought.

Ninja ants in the second test tube from the bottom, separate queen in the right-most catch tube.
Stay tuned to find out what is in the other tubes in the coming weeks.

So this unknown ant species was polygynous and quite strongly so. This added a rather oddly shaped piece to the puzzle of identifying them. I spent many hours on my phone the next week going over this list of known Romania ants, knowing they had to be Myrmicinae as they had the distinctive two-button petiole between thorax and gaster, but unable to narrow it further down to the genus:

Messors (multiple castes of workers, seed eaters and not to be found in humid ground)
Monomorium (pharaonis is the only species, right size, but not indigenous and wrong color)
Myrmica (large and diverse genus but much larger species and also very dominant hunters)
Solenopsis (right size aside from queen, likes living close to other species, but wrong color)
Temnothorax (comparable size and correct attitude, but wrong color and typically no dirt nests)
Tetramorium (similar color and shape, but monogynous and much larger queen)

Not being able to properly identify the species meant no information about their habits or required care. Thus we didn't know yet that this species doesn't do claustral founding very well, but colonies tends to adopt freshly mated queens to later split colonies instead. Sadly that meant that the little queen we had found earlier (shedding her wings a few days later) didn't survive being kept in a catch tube on her own for a week.

It wasn't until we got home (the colony seemed quite content with living in their test tube) that I was able to make better pictures and have a much better look at them. That I was able to discern their true identity. Surprisingly it turned it actually was on the Romanian ants list, but I just had never heard of the Cardiocondyla genus before, so I kind of overlooked it.

No erect hairs on the thorax, small propodeal spine at the end of the thorax
and the postpetiole is much wider that the petiole: Cardiocondyla

We had some difficulty coming up with a name for them though, as this is our first polygynous ants that actually has multiple queens. We ended up with naming them after the village where we found them: they are the 'Georgies'.

Our plan is now to split up the colony into two, so we can experiment a bit in order to determine their nesting preferences. In the next update on our tiny ninja ants I'll tell about how this worked out and I'll show some of our awesome ant-keeping tools I used for this. But first there are a lot more ants waiting for their turn to be properly introduced to our readers!