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.