The purpose of the abduction of brood was not simple predation: once they eclose, the Formica fusca will assimilate into their abductor's society, caring for the brood of F. sanguinea without a fuss. They are treated as full members of the colony into which they were inducted: a behavior termed dulosis. Humans (English-speakers at least) have colloquially called it "slave-making" for 203 years; this popularity belies fundamental dissimilarities between human slavery and dulosis, which I iterated in a message-board rebuttal some five years ago:
"Furthermore, referring to some kinds of ants (such as Harpagoxenus and Polyergus) as “slave makers” is another sad example of ants being anthropomorphized by uninformed laymen. Calling them 'adopters' or 'foster families' would be more accurate. While it is true that ants that practice dulosis (a behavior in ants that humans often inaccurately term as 'slavery') brutally kill other ants to capture those ant’s pupae, those ants that emerge from the said pupae are brought up as members of their foster colony and are never discriminated from their 'enslavers,' as far as myrmecologists can tell. I define slavery as being the capture of a member of your own species and the coercion of that individual to do work that you consider too dirty, dangerous, or dull (DDD, if I may utilize an acronym originally used in robotics) for you to do yourself: on the other hand, while the notorious dulotic myrmicine ant Strongylognathus emeryi, for instance, makes those ants that it has “enslaved” do work that it never does (namely, feeding other S. emeryi members of the colony), this is not because it is unwilling to do this work itself but because it is unable to, because the gigantic mandibles it possesses are (get this!) too massive and clumsy to do anything but slice apart other ants. Dulotic ants never enslave their equals [those of the same species]—the closest human analogy to dulosis would be a human family stealing a baby monkey from its parents, bringing it up as one of their own, and training it to answer the telephone because the humans did not have an answering machine and were usually too busy to answer it themselves." [July 9, 2009]
...I need not even mention the racial baggage that is hauled into the harsh light whenever the word slavery is mentioned, not only in the United States but elsewhere around the globe. Thus, it would behoove us to phase out the term in myrmecological situations: not motivated by some fearfully reflexive desire for political correctness, but because science is a search for truth; and to call the behavior I saw for myself back in August "slavery" is nothing but an untruth. But what should the vernacular substitute be?
First let us ask: why bother with such a substitute? Couldn't we simply use "dulosis"—a term specifically coined for the syndrome it denotes, and not a verbal hand-me-down from some unrelated activity—and call it well and good? I would be the first to say yes, but many would disagree. You see, dulosis is an attention-grabbing behavior: one violent enough to hold the interest of the general public, at least during those brief intervals when TMZ and its ilk are inactive. The sciences require the investment of the masses in order to thrive: and anything scientific that can compete with twerking pop stars is in need of a good vernacular name. (Assuming that the body politic consists mostly of infantile yahoos, which may not be so axiomatic as is thought.)
Professor Joan Herbers put it this way in an article pointing out the inappropriateness and repellent connotations of the "slave-making" simile (underlining mine):
Yet discarding metaphors altogether in favor of obscure jargon is incompatible with interesting students and the public in my work. While no metaphor can be perfect, I offer an alternative. I suggest that we replace “slave-making ants” with “pirate ants.” Pirates certainly take captives when they board ships, and pirates rely on forced labor. We can replace “slave” with “captive” and “dulosis” with “leistic behavior,” from the Greek for pirated spoils, leistos. To be sure, the pirate metaphor has its own imperfections when we use it to describe ant behavior—but the social impact on audiences, if anything, might be positive. I, for one, prefer audiences to identify my work with Captain Jack Sparrow than with Simon Legree.I submit that we scientists have a responsibility to communicate effectively. To do so, we must listen to those who study the impact of words. If the terminology we use is degrading or offensive, then it is time to change the terminology. (Herbers, 2007)
One wonders if Professor Herbers considered that she might have hereby offended the countless hostages who have been held by the pirates active off the Horn of Africa in recent years; or that making a plea to something as fickle as pop culture to lend weight to a scientific concept is distinctly unconvincing. (Honestly, who will remember that "Pirates of the Caribbean" even existed in a few more years?) In any event, piracy just as much as slavery is a conspecific activity driven by trade: essentially different from dulosis.
Sainted macrophotographer/myrmecologist Alex Wild proposed "kidnapper ants" (Wild, 2013) for his part: if dulosis could be called "forcible adoption", then perhaps kidnapping is the best human analogy we have. There are downsides to the phrase: yet again, by doing so we liken dulosis to a human activity often motivated by profit—and this desire for monetary aggrandizement is unique to Homo sapiens. Moreover, kidnapping is not usually motivated by a need for labor.
Bernard Werber, in Le Jour des Fourmis (1991), drew a comparison between ant "slaves" and the yeniçeri ("new militia") of the Ottoman Empire, anglicized as "janissaries" (p. 236) (this analogy was also noted by Benoit Guenard in Myrmecos' comments section): these warriors were abducted as children (a practice called devşirme) and indoctrinated to form the Sultan's personal bodyguard; drawn from Christian communities of the realm, they would fight loyally against their own kin (Werber, 1996). Shall we then call slave-makers "devshirme-ants"? Possibly, but even here we risk giving offense to the Armenians and Greeks from whom the janissaries were drawn by the Turks, and who still remember their old oppression.
In the end, I must say that "kidnapper ant" will suffice; although for my part, dulosis (or the synonymous cleptergy) is a superior sobriquet. Why did I wait until December to write all this? A lack of time to complete the counterpart post on my personal blog, which situates dulosis in its broader ethological context: for ant-kidnapping is but one aspect of the phenomenon known as social parasitism. (Be sure to read Part 1 first.)
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Herbers, J. M. (2007). Watch your language! Racially loaded metaphors in scientific research [electronic version]. Bioscience, 57(2), 104-105. Retrieved 12/27/13 from http://www.jstor.org/stable/full/10.1641/B570203#rid_i0006-3568-57-2-104-b2
Werber, B. (1996). Empire of the Ants. New York City: Bantam Books.
Wild, A. (October 24, 2013). Polyergus moves forward, and a modest proposal for kidnapper ants. Retrieved 12/24/13 from http://www.myrmecos.net/2013/10/24/polyergus-moves-forward-and-a-modest-proposal-for-kidnapper-ants/