How should we talk about Army Ants?


Neivamyrmex army ants attacking a pavement ant, California

I see this morning that Daniel Kronauer has published a review of army ant biology in Myrmecological News.  The paper, among other topics, attempts to straighten out some key terminology:

AenEcDo army ant: a connotation free abbreviation that is introduced here to avoid the term "true" army ant. It collectively refers to species in the three subfamilies Aenictinae, Ecitoninae, and Dorylinae and is strictly taxonomically defined.

Army ant: any ant species with the army ant adaptive syndrome.

Army ant adaptive syndrome: a life-history characterized by group predation, nomadism, permanently wingless queens, and dependent colony founding.

Driver ant: a term coined by SAVAGE (1847), only to refer to African Dorylus species of the subgenus Anomma that "drive" fleeing arthropods in front of epigaeic swarm raids. Because the same phenomenon also occurs in some New World army ants of the genera Eciton and Labidus, the term has generated confusion and usage should be avoided. Furthermore, it has been used inconsistently (e.g., GOTWALD 1974 also referred to the leaf-litter Anomma species as "driver ants").

True army ant: a term coined by WILSON (1964) to collectively refer to the subfamilies Aenictinae, Dorylinae, and Ecitoninae. Alternatively, the term "classical army ant" has been used (e.g., WITTE &MASCHWITZ 2000, BERGHOFF & al. 2003a). Because both terms incorrectly seem to suggest that army ants outside these three subfamilies are not "real" army ants, they are not particularly useful and I recommend avoiding their usage.

We biologists can classify organisms in several ways.  Two of the most common approaches employ function, where species that show similar behaviors are grouped together, and evolution, where groups are defined by their shared ancestry.  Either can be useful, depending on the context.

Daniel puts his finger on the confusion caused by mixing these two fundamentally different ways of talking about organisms.  In this case, the confusion between referring to a single, large evolutionary lineage of ants sharing a particular behavior by inheritance, and the aggregate of all ants- including those from other lineages- that show the same behavior.

With army ants, the two approaches circumscribe different sets of species.  Authors who write about "army ants" must further clarify whether they mean members of the Dorylinae, Ecitoninae, and Aenictinae, or whether they mean nomadic, group-raiding ants with wingless queens.  For instance, Simopelta is an army ant by all behavioral indicators, but it is a ponerine, not at all closely related to the dorylines and ecitonines.

Daniel proposes that "Army Ant" refer to the functional category.  Sounds good to me.  I'd like Simopelta to be an army ant, because that is what it is.  He also proposes the positively Frankensteinian "AenEcDo army ant" as a replacement for what we've traditionally called army ants.  Of that mouthful, I am skeptical.

The subfamilies Aenictinae, Aenictogetoninae, Ecitoninae, and Dorylinae do form a clade, so it seems to me the natural solution would be to provide a proper taxonomic name.  One Linnean solution, for example, could be to sink all the Dorylomorphs into a single subfamily, the Dorylinae (a good idea for plenty of other reasons), and assign a tribe name- the Dorylini- to those groups that inherited the army ant syndrome.  Or, if one is not of the Linnean persuasion, one could adopt a rank-free clade name. Say, Dorylia.

I also disagree with dismissing the term "driver ant".  Driver ant is not a functional category at all but a vernacular common name, one that is sometimes applied to a particular clade of African species.  Of course the term should be avoided in scientific publications, but that's only because technical publications should use scientific names over common names anyway.  It's not the purpose of common names to be standardized or otherwise controlled.  Common names are supposed to be free-form, colorful, and reflective of the varied local cultures.  The research community should use the clade name Anomma.

Finally, I'd like to point out that I've made it all the way through this post without a single wisecrack about being pedANTic.

source: Kronauer, D. J. C. 2008. Recent Advances in Army Any Biology (Hymenoptera: Formicidae). Myrmecological News 12: 51-65. Online Earlier.

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Thanks for your thoughtful comments Alex - here is a quick reply, hopefully without seeming ANTic:

First, as I discuss in the review, I donât believe that the contention that Aenictinae, Aenictogitoninae, Ecitoninae, and Dorylinae form a clade is as well supported as you suggest. Until this issue is resolved, it doesnât seem wise to adopt a ârank-free clade nameâ or tribe name based on shared ancestry. And even if it should turn out that we are talking about a clade, this clade will contain Aenictogiton (the sister to Dorylus) of which we donât even know the workers, let alone anything about the life-history and general resemblance to army ants. Therefore, your âDoryliaâ would not be equivalent with Wilsonâs âtrue army antsâ. And have you ever tried to write a review article on army ants in which you attempt to avoid the term âtrue army antsâ and you are space limited? âArmy ants in the subfamilies Aenictinae, Ecitoninae, and Dorylinaeâ is quite a page filler and sounds a bit awkward after youâve said it three or four times.

Second, âdriver antâ, what a beautiful name! Of course you can call some of the African army ants âdriver antsâ and you can also call their males âsausage fliesâ if you want to. But because the terms are not strictly defined, you should not do so in scientific publications (or, if you decide to do so, define each time what exactly you mean). As others have before you, you imply that âdriver antâ means the species in the subgenus Anomma. However, this subgenus also includes leaf-litter hunting species which have not normally been considered âdriver antsâ (although sometimes they have). Furthermore, the subgenus is not monophyletic (Kronauer et al. 2007 BMC Evol. Biol.). I made this attempt at simplifying army ant related jargon because people have been repeatedly confused by different terms that mean the same thing and terms that people use to mean different things. In science it is best to avoid superfluous and ill-defined terms, but I agree with Alex that it sounds much cooler if you tell your friends that you've been attacked by an army of African driver ants than saying that you've been bitten by some epigaeically hunting Anomma. But anyway, next time you are wondering whether this legionary ant is actually a true army ant or a driver ant, instead of emailing me, consult my review and youâll find out.

By the way, great website Alex!