Workers of Polyergus mexicanus return from a successful raid with kidnapped Formica subsericea brood. Urbana, Illinois.

This morning saw the publication of James Trager’s much-awaited taxonomic revision of the parasitic ant genus Polyergus. These insects are commonly known as “slave-raiding ants”, a controversial moniker I’ll discuss in a bit. But first, the new paper.

James, who often comments on this blog, is known for thorough, methodical taxonomic papers on particularly difficult genera of ants. In the 1980s, for example, he revised the North American Nylanderia and Paratrechina. As James is no longer employed as a researcher, his publications are infrequent. But his patience and attention to detail lend James’ works particular longevity. This new revision fits the mold, so I expect it will be the standard reference for identifying Polyergus to species for the next decade and beyond.

(An aside: A taxonomic revision is what it sounds like. The existing taxonomy is reevaluated based on new data, new species are described if needed, old mistakes are corrected, and inadequate taxa are sunk into more appropriate ones. The result is a more stable arrangement of species.)

The old scheme for Polyergus crammed an uncomfortable level of variation into just a handful of described species. Yet consistent morphological differences among Polyergus that attack different species of host Formica, particularly in the F. pallidefulva group, suggested a much finer division. The new scheme is more sensible in light of host/parasite biology, elevating a number of subspecific taxa to full species while describing five as entirely new. The paper also contains fascinating observations on Polyergus natural history.

And what a spectacular natural history these ants have!

Colonies of Polyergus cannot function without a large contingent of workers from another ant genus, Formica, that care for the brood, maintain the nest, and forage for food. In fact, Polyergus workers themselves do little other than kidnap immature brood from nearby Formica nests. The raids are usually in late afternoon, in the summer, and can be spectacular to watch.


At the entrance of a Polyergus mexicanus colony, a Formica subsericea worker carries excavated soil from the nest. The parasitic Polyergus workers do not perform those sorts of tasks. (Urbana, Illinois)

The dependence of Polyergus on stolen labor has lent a bondage metaphor to the common name: slave-raiding ants. To the limited extent that a human analogy can apply to an insect, the comparison is reasonably apt.

Recently the slave-raiding name has become controversial. For good reason. Myrmecologist Joan Herbers (2006, 2007) observes that references to slavery can make public communication about these ants unduly difficult:

In the United States, we are technologically dependent yet scientifically illiterate, and using jargon that discourages even one individual from learning more about science is simply irresponsible. I find it hard to imagine a young black student being attracted to a discipline that calls parasitized insects “slaves” and “negro ants.”

Herbers proposed substituting “pirate ant” for “slave-raiding ant”, yet I’ve never liked that solution. A couple years ago I explained:

I don’t think Herbers’s solution is workable, though. Piracy is a terrible parallel to what ants like Protomognathus and Polyergus do. Pirates take things. Slave-raiding ants aren’t primarily pillaging the food stores of other colonies. They don’t lay in wait along trails to steal forage. No. The brood parasites take actual, living ants whose labor they use for their own benefit. That is slavery. If I call these ants pirates, I am not communicating accurately about their biology. Piracy, for me, is out.

While I still don’t like the piracy metaphor, I’ve come around to Herber’s perspective that the slave-raiding comparison, while apt, is not ideal for those of us trying to introduce myrmecology to its broadest possible audience.

So. Down with ant slavery! Instead, I humbly propose that Polyergus and other cleptergic species be called kidnapper ants.

As a vivid vernacular, kidnapping is as accurate as slavery. Polyergus raids target immature forms of its hosts, after all. Yet kidnapping, though terrible as a human atrocity, is not so culturally encumbered as slavery.

I tried out the phrase on a local church group recently. Given how quickly attendees sat forward in their seats on mention of the mysterious Kidnapper Ants, I’ll stick with the newer metaphor.

Anyway. Regardless of what you think of the common names, check out James’ revision. It’s good.

Herbers, JM (2006) The loaded language of science. Chronicle of Higher Education. 52: B5
Herbers, JM (2007) Watch Your Language! Racially Loaded Metaphors in Scientific Research. BioScience 57. doi 10.1641/B570203
Trager, JC (2007) Collected thoughts on “pirate” ants and “leistic” behavior. Notes from Underground, online.
Trager, JC (2013) Global revision of the dulotic ant genus Polyergus (Hymenoptera: Formicidae, Formicinae, Formicini). Zootaxa 3722 (4): 501–548.