Why only one taxonomic family for all ants?

I have recently wondered why all ants are placed in one family Formicidae, if you look at how diverse the subfamilies are from each other - for example, Myrmicinae, Formicinae, Ponerinae, Dolichoderinae, Ecitoninae, etc. I believe there are currently 15 ant subfamilies. If you look at other Hymenoptera, bees for example, are divided into 5 families, wasps into many families. Could it be because not all bees and wasps are social, but all ants are ? If that is the case why are termites which are all social put in 4 different families in North America? It seems some of the ant subfamilies are as diverse or more so than the termite families are from each other. Or am I missing something that puts all ants in one family? If I am please let me know.
I hope this is not a dumb question.

Mike M. -- Orange Co., CA

This is not a dumb question at all, Mike. Ants are quite diverse in form, and there are clearly some well-defined monophyletic lineages (though those who study higher taxonomy of ants might not agree the number is your suggested 15). However, the subfamilies vary in age and level of internal diversification, so even their ranking as presumably equivalent subfamilies is itself arbitrary. On the other hand, it is true that as a group, ants are a coherent, monophyletic lineage among the stinging Hymenoptera, with no apparent close relatives, perhaps one reason we consider them a single family. But in taxonomy, rank above the species level is arbitrary, and in this case, ant taxonomists have simply settled on the convention of treating all ants as one family. As Chicago Field Museum myrmecologist, Corrie Moreau, says, "Higher taxonomic ranks are certainly arbitrary. There are more ant species than birds and there are tons of bird families."

I received this additional comment from Dr. Phil Ward, one of the world's premier ant systematists. "The rank of taxa is quite arbitrary (as you say James), and largely a function of idiosyncratic taxonomic history. There is no such thing as a family-level difference or a phylum-level difference. So, families of Hymenoptera are not equivalent and there is no objective way to assign family-level rank. A ranked classification can be justified only from a practical (as opposed to objective) point of view. A ranked phylogenetic classification (i.e., a ranked classification where all supra-specific taxa are monophyletic) has the wonderful property that the taxa of any given rank are mutually exclusive. Very handy for sorting and curating specimens, and perhaps organizing information."

James C. Trager of the AskAnt Team

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