Introducing Tetramorium immigrans: a better name for the long-established pavement ant

No longer fighting over a name.

Meet Tetramorium immigrans. 

I have never been more pleased to report a taxonomic name change than this one. Long called “Tetramorium caespitum”, then “Tetramorium species E” once it became clear the Eurasian T. caespitum was a complex of cryptic forms, the pavement ant has spread across the world and is now among most common urban ants in North America. After decades of confusion, Herbert Wagner has published a fine monograph on the taxonomy of the species complex. Among Wagner’s many discoveries was that Santschi’s 1927 “immigrans” was valid for this world-traveller. An apt change, and a fine resolution of a long-standing problem.


How Should Taxonomists Name Your Favorite Ants?

Are these two Temnothorax, or one Temnothorax and one Protomognathus?
Are these two Temnothorax species, or one Temnothorax and one Protomognathus?

Last year, a team of Antweb-affiliated myrmecologists published an evolutionary study concluding, among many results, that a slate of socially parasitic genera had evolved from within their host genera. The names of parasitic genera were subsequently sunk. Inclusion of derived groups in their parent genera has been standard practice for decades as a way to keep names consistent with ancestry.

But a number of myrmecologists do not approve of their favorite ants losing their names, and struck back with a strongly worded opinion in Insectes Sociaux this week:

We contend that banning all paraphyletic groups while simultaneously executing binominal Linnaean nomenclature results in a taxonomy going off the rails.

The dissenting authors make a lengthy argument about information content, evolution, and practicality, but the logic distills to, “the sunk genera look different, and we feel it more useful that the difference is reflected in a unique name.” If this argument looks familiar, it is the same case put forth by Ernst Mayr’s “Evolutionary Taxonomy” school in the 1960s and 70s. This was not a winning argument. Most biologists found disagreements about trait differences subjective compared to the relatively clarity of ancestry, and taxonomists today generally agree that recognizing paraphyletic groups is more confusing than the alternatives.

I have little personal experience with the genera in question. From my perspective as an outsider, I had to look up Epimyrma in Bolton’s catalogue to figure out what kind of an ant it was. Formicine? Myrmicine? Had I known it was basically a parasitic Temnothorax, I’d have been that much ahead of the game. Monophyly is information; paraphyly less so. But utility is a question of perspective and context, I suppose, and I can empathize with those who regularly work with these ants. Treating these distinct species as congeners may be as awkward as attending a party where everyone is named Jayden.

Still, given the volumes of vituperative ink spilled a half-century ago in the cladism wars, and the weight of the pro-monophyly consensus among all biologists, I suspect this renegade group of ant scientists will be fighting an uphill battle.

Disclosure: I eclosed as a myrmecologist from Phil Ward’s lab, so of course I am not without my allegiances.

Sources: Seifert, B. et al 2016. Banning paraphylies and executing Linnaean taxonomy is discordant and reduces the evolutionary and semantic information content of biological nomenclature. Insectes Sociaux doi: 10.1007/s00040-016-0467-1

Ward, P.S. et al 2015. The evolution of myrmicine ants: phylogeny and biogeography of a hyperdiverse ant clade (Hymenoptera: Formicidae). Systematic Entomology, 40: 61–81. doi: 10.1111/syen.12090

A Myrmicine Phylogeny Shakes Things Up

Monomorium kiliani
Monomorium kiliani, an Australian myrmicine. The narrow, two-segmented waist is characteristic of this subfamily.

We’re only halfway through the year, but already 2014 will be remembered as pivotal for studies of ant evolution and classification. Following right on the heels of Schmidt & Shattuck’s massive ponerine revision comes an important new study from the Ant Tree of Life group. Ward, Brady, Fisher, and Schultz (2014) have reconstructed the first thorough genus-level phylogeny of the great ant subfamily Myrmicinae.

How important is this study?

Roughly half of all ants are myrmicines, both in abundance and in species diversity. Their numbers include fire ants, harvester ants, leafcutter ants, big-headed ants, acrobat ants, and so on, to the tune of some 6,000+ species.

So… Boom! Suddenly, we’ve been given a detailed picture of the evolution of half the ants. This is big. It is so big I cannot cover the paper in detail. Instead, I’ll just give a few preliminary thoughts, as follows:

1. This is a well executed study, as we’ve come to expect from the Ant Tree of Life team, applying a thorough analysis to over 250 carefully selected taxa and 11 genes. It’s also a shining example of an older generation of genetic techniques, alas, and while I am confident the stronger results will mostly endure, be aware that an incoming next-gen tide of full genomes, and the 6,000 yet-unsampled myrmicine species, may yet overturn some of the findings.

2. The deep history of Myrmicinae, starting 100 million or so years ago, mostly occurred on those continents that drifted to become the Americas. Echos of these earliest divisions are heard in six clear, genetically distinct groups that Ward et al have formally set the up as a new system of tribes, replacing an earlier, messier scheme. The six groups are listed here in their order of divergence: Myrmicini (MyrmicaManica), Pogonomyrmecini (Hylomyrma & Pogonomyrmex), Stenammini (AphaenogasterMessorStenamma, and relatives), and three sprawling groups with thousands of species: Solenopsidini, Attini, and Crematogastrini. 

The myrmicine big picture. (Sharpie on office paper, 2014, limited edition print available, unless I recycle it).

3. The news is not all good. The clarity deep in Ward et al‘s tree fades for slightly younger events. Early relationships within some of the the six tribes are discouragingly ambiguous. This study has resolved some problems, myrmicine taxonomists face a difficult road ahead. Many of the world’s greatest genera do not form natural groups and will have to be redone. These include Aphaenogaster, Pheidole, Tetramorium, and especially Monomorium, which splatters almost comically across the Solenopsidines.

What, really, is Monomorium? Modified from Figure 1 of Ward et al (2014).

Distressingly, fuzzy resolution in a data set with this many markers and taxa means achieving proper resolution, if at all, will likely be expensive. Myrmicines may have speciated so explosively that we may never be able to reconstruct what happened with confidence.

4. The authors correct a few of the more obvious instances of paraphyly. Notably, the New World “Messor“, being unrelated to their old world doppelgangers, were moved to a revived Veromessor, and several social parasites like Protomognathus and Anergates have been sunk into the host genera from whence they evolved: Temnothorax and Tetramorium, respectively. There are other changes, too; they are listed in the abstract

Most of the identified problems- such as what to do with Monomorium and Aphaenogaster were left for targeted future research.

5. Remember the dispute over Pyramica vs. Strumigenys? The argument was fundamentally over how ant mandibles evolve. Apparently, high energy trap-jaws arise easier than anyone imagined. According to Ward  et al, not only is the assemblage of trap-jaw ants formerly included in dacetini a polyphyletic splatter, even within the genus Strumigenys the trap jaw has arisen at least twice.

A phylogram of Strumigenys, modified from Figure 1 in Ward et al 2014, showing strong support for the parallel evolution of trap-jaws in the genus.

6. The rare and bizarre African myrmicine genus Ankylomyrma is not a myrmicine at all! Rather, Ward et al‘s results unambiguously tie it to the equally bizarre Tatuidris of the Neotropics, sitting on a distant branch of the ant tree. Peas in a poneromorph pod…

Ultimately, Ward et al have crafted a sobering view of how little we still know about ant evolution, and how much remains to be done.

Aphaenogaster fulva, photographed in Illinois.

source: Ward PS, Brady SG, Fisher BL, Schultz TR (2014) The evolution of myrmicine ants: phylogeny and biogeography of a hyperdiverse ant clade (Hymenoptera: Formicidae). Systematic Entomology, online early. DOI: 10.1111/syen.12090

disclosure: I received my Ph.D. from Phil Ward’s lab where much of this study was completed, and I contributed a few of the samples, but I was long gone by the time the study was initiated and have had no other involvement with the research.

Everything Old Is New Again – Ponerine Taxonomy Returns To Its Roots

Pachycondyla striata, from Brazil, is one of the few names to remain stable after Schmidt & Shattuck fragmented Pachycondyla.

A monumental day for ant taxonomy! The mythical Schmidt & Shattuck ponerine revision, long rumored to be in the works, has emerged from the mists of legend and lore. It’s real! All 242 pages are in Zootaxa:


I don’t wish to speak for the entire myrmecological community, but I think it is safe to say that Chris Schmidt and Steve Shattuck’s ponerine revision has been the most awaited taxonomic paper of the past decade. Ponerine ants comprise one of the greatest subfamilies in terms of abundance and species diversity, particularly in the tropics. Ant people know ponerines. The group is the most purely predatory of the large subfamilies and contains some spectacular insects: trap-jaw ants, matabele ants, various and sundry predators and huntress ants.

Schmidt & Shattuck’s paper is significant for two reasons. First, nearly all ant researchers will be affected by the taxonomic changes. And second, the changes themselves are large, especially for the hundreds of species that used to belong to the sprawling polyphyletic genus Pachycondyla. Under the Schmidt & Shattuck hammer, Pachycondyla in the strict sense remains just a shadow. All but a handful of Neotropical species move to 19 different genera, some new, most revived from older literature. There are about a third more ponerine genera to learn than there were yesterday. That’s a lot to digest.

You might think such large changes would invite controversy, but I anticipate that the new scheme will be widely accepted and largely stable.

1. The work itself is thorough, involving morphology and several different genetic markers. There is good reason this paper was years in the making.
2. Many of the newly valid names are resurrected from the older literature, and as such they already reflect gross morphological groupings as seen by earlier generations of myrmecologists.
3. Ant taxonomists are more uniformly phylogenetic in their outlook than the preceding cohort. The polyphyly of Pachycondyla was not an accident born of ineptitude; rather, it was designed that way by Bill Brown, who was operating under a different philosophy of systematics more popular in the middle of the last century. Since Brown’s school has faded from prominence, most biologists are uncomfortable with polyphyly. As Schmidt & Shattuck are dragging ponerine taxonomy back into the comfort zone of most evolutionary biologists, I expect the new scheme will be popular.

In the big picture, Schmidt & Shattuck have put this important group of ants on a stronger taxonomic foundation. In the small picture, we are faced with the mundane realities of re-memorization.

Pachyondyla apicalis? No longer. Get used to Neoponera apicalisPachycondyla stigma? Nope. It’s Pseudoponera stigma. Plus, there’s Brachyponera, PseudoneoponeraMesoponera…

source: Schmidt, CA, Shattuck, SO (2014) The Higher Classification of the Ant Subfamily Ponerinae (Hymenoptera: Formicidae), with a Review of Ponerine Ecology and Behavior. Zootaxa 3817 (1): 001–242.


How To Tell The Difference Between the Japanese Pavement Ant And The Common Pavement Ant

Urban ant collectors across temperate North America are undoubtedly familiar with the pavement ant Tetramorium caespitum*. This small brown insect is as common as dirt along sidewalks.

The pavement ant is not native here. Rather, it is a European species that proliferates in the novel habitats where Americans added cement and paving stone to previously uncapped, pavement-free soils. Since we love our sidewalks and our asphalt, we have created a lot of ant habitat and a lot of pavement ants.


Identification of the pavement ant in North America was straightforward until recently. Tetramorium caespitum is a small, blocky, brown ant with a squareish head, a two-segmented waist, a series of lengthwise ridges on the head, two nubbin-like spines on the propodeum, and an antennal socket with a distinct ridge as described here.

This diagnosis failed in the 1980s when an extremely similar species was introduced to St. Louis. The newcomer, the Japanese pavement ant Tetramorium tsushimae, is so similar in appearance to its European congener that correct identification even under high magnification involves measuring several body parts on a sample of workers and performing statistical analyses. On average, the new introduction is slightly smaller and with slightly larger propodeal spines. Your chances of nailing the ID based on a single worker aren’t great.

Tetramorium tsushimae
There is one easy identification trick that works pretty well at low magnification in the field, though. The trick is worth learning, because Tetramorium tsushimae appears to be more aggressively invasive than the common pavement ant and may become more common as it spreads from Missouri and Illinois.

Here’s the trick:

Colonies of the Japanese pavement ant usually host a great deal more color variation in the workers.

While older T. tsushimae are uniformly dark, the same as their European counterparts, younger workers are strongly bicolored, with a light thorax, giving colonies a more varied appearance. This difference should be visible in the photograph above.

Now that you can spot the difference, keep an eye out for T. tsushimae. It could show up many places where T. caespitum is currently king.

*sometimes called “Tetramorium sp. E.”, for reasons too lengthy to discuss here.

source: Steiner, Florian M., Birgit C. Schlick-Steiner, James C. Trager, Karl Moder, Matthias Sanetra, Erhard Christian, and Christian Stauffer. 2006. Tetramorium tsushimae, a New Invasive Ant in North America. Biological Invasions 8(2):117-123.


Accidental Robot Taxonomy

Here’s a find that will disturb any self-respecting taxonomist:


This book is not a book. It’s an unpublished student thesis from the University of Texas at El Paso.

Apparently Bibliogov, a publishing company that scrapes state websites and repackages content to sell to unsuspecting buyers, has picked up the deposited thesis and is printing it on demand. The research was not completed to the point of submission to a peer-reviewed journal, and neither the student nor her adviser intended to publish the work. At least, not in the current form. The thesis was merely filed as a requirement for the student to graduate.

This sort of robo-publishing would not normally be a problem but for the legalistic nature of how taxonomic names are regulated. Publishing is a formal act that makes taxonomic names available. Third party printing potentially legitimizes taxonomic proposals never intended for release. Not good. Taxonomy already has enough chaos without robots jumping the gun.

Should the practice of scraping and publishing theses become common, either the International Commission on Zoological Nomenclature will have to adopt a set of rules suppressing involuntary publication, or students of taxonomy should be uniquely exempt from filing dissertations with unpublished results.

(via James Trager)

[update: to clarify, these robo-books don’t automatically make a name available under ICZN rules. A couple other conditions about the timing and deposition of the content must be met that may or may not be the case.]

Ten New Temnothorax

Temnothorax caguatan Snelling, Borowiec, and Prebus 2014 from Jasper Ridge Biological Reserve, California, USA.


The great Roy Snelling has posthumously published a revision of California’s Temnothoraxwith the humous assistance of Matt Prebus and Marek Borowiec. The paper provides an illustrated key to species, range maps, and descriptions of ten new taxa. Among the newbies is Temnothorax caguatan, a common ant we’ve been awkwardly calling “the species sort of like T. rugatulus that nests in trees”. At last! A real name. The etymology of this entomology is given as:

When Hernán Cortéz was conquering central Mexico, the Nahua speaking people related to him tales of a fabulous land, ruled by women, far to the northwest that was rich in gold and gems. They named this land “Caguatán”, the Land of Women. This tale presumably inspired Cortéz and other avaricious conquistadors to search for this marvelous land, ultimately leading the Spaniards to the Californias.

If you’ve ever wondered why no single easy reference book exists for identifying North America’s ants, this is the reason. The state of taxonomy remains more rudimentary than you’d think, with many species still nameless or poorly understood. A few dozen more studies like Roy’s and someone will finally be able to give our ants a decent guide.

source: Snelling R, Borowiec M, Prebus M (2014) Studies on California ants: a review of the genus Temnothorax (Hymenoptera, Formicidae). ZooKeys 372: 27-89. doi: 10.3897/zookeys.372.6039

How to identify the bullet ant, Paraponera clavata

Bullet ant, Paraponera clavata, Jatun Sacha reserve, Ecuador.


The most infamous ant in the world is surely the tropical American bullet ant, Paraponera clavata. This conspicuous insect is known for an unusually painful sting. It is not the only big rainforest ant, however, and other species are frequently mistaken for it.

Here is how to make sure that big ant you saw was really a bullet ant.

bullet ant range

1. Check your location: in the wild, bullet ants are only found in low-elevation forests from Honduras south to Paraguay. If you are not in Central or South America, you don’t have a bullet ant. (source)

2. Check the size: bullet ants are not just large, they are massive – over an inch long. They look like plastic toy ants brought to life.

3. Check for the characteristic thoracic horns. Bullet ants have a pair of blunt horns on the first segment of the thorax. No other ant its size has the horns.


4. Check the shape of the petiolar node. The waist of the bullet ant has a sharp, forward-leaning triangular node.



With these criteria in mind, here is a real bullet ant:

South America? Check. Massive? Check. Horns? Check. Forward-pointing waist segment? Check.

For comparison, these other large South American species are not bullet ants:

Dinoponera is big- even a bit bigger than the bullet ant, but Dinoponera is darker in color and lacks the horns on the thorax.
Ectatomma tuberculatum is an ubiquitous big rainforest ant with a shape confusingly similar to that of the bullet ant. But Ectatomma is too small, as are the horns, and the waist segment is the wrong shape.
Pachycondyla villosa is common and also packs a painful sting, but this large species is not big enough to be a bullet ant and it lacks the horns.
Atta leafcutter ant soldiers are big and even have the thoracic horns, but they aren’t big enough, they lack the right waist shape, and are their overall body proportions are different.
Cephalotes atratus black turtle ants are common and conspicuous, but they are much smaller than bullet ants and have sharp spines rather than blunt horns.
The golden carpenter ant Camponotus sericeiventris is not quite big enough, its horns are more forward on the thorax, and it doesn’t have the right waist shape.

 With any luck, you should now be able to check the identification of your purported bullet ant without having to run a sting test.