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of its social baggage, however, another problem with calling the ants slave makers is that, as with the army ants, it gives an entirely incorrect view of what the ants themselves are doing. Hölldobler and Wilson's point about domesticated animals versus forced labor from members of the same species aside, most biologists, including them, classify the behavior as a kind of parasitism. In other words, the so-called slave makers are acting like exceptionally free-roaming tapeworms. Like the tapeworm, the slave makers, at least the obligate species, make their living entirely off of another organism, the host. But instead of traveling passively from one host's intestinal tract to another via, say, a contaminated bite of meat, the ants take matters into their own six legs. The slave raids, with the excited workers rushing to and fro with their cargo of pale cocoons, are just a more visible and dramatic version of the worm in the gut ensuring it will have someone to provide it with a steady supply of meals for the foreseeable future. Even Crompton notes that "a slave-raiding expedition is not really a battle, it is a routine commercial undertaking."

Admittedly, this analogy is not perfect, and the ants are what scientists call social parasites, rather than internal ones. Cuckoos and cowbirds are the most familiar examples of such animals: the cuckoo female lays her eggs in the nest of another bird species, exploiting the parental behavior of the host, who rears a genetically unrelated chick. The hosts have, in a sense, adopted the enemy to their own advantage, gaining the labor of others at little expense. And Maeterlinck points out that the captive ants do exactly the same thing that they would be doing in their own nest, namely, feeding the workers and caring for the queen. Their lives are no harsher than they would be in their own nest, and the everyday life of any ant is pretty grim by anthropomorphic human standards at least. But those pejorative declarations about degeneracy from Crompton and Maeterlinck fit right in with this point of view. Tapeworms and many other parasitic organisms have reduced limbs, eyes, and other organs, a state of affairs that probably evolved because the appendages are unnecessary, maybe even an impediment, in the dark cozy confines of the host's gut. Crompton's prediction about the extinction of the slave makers may be off the mark, since of course parasites show no signs of going out of business. Seeing slave making as a form of parasitism gives rise to the unsettling thought that, by the same token, we are a kind of slave to our own pathogens.

Viewing the interaction as parasitic not only sidesteps the terminology melodrama, it clears the way for asking other interesting questions. Herbers and her colleagues have examined variation across the range of several species of pirate ants regarding which species they exploit, and, as with a disease-causing organism, talk about the "virulence" of different raiding species. Just as anthrax is more virulent than athlete's foot, by doing more damage to its host, a more virulent social ant parasite kills a larger proportion of the adult ants at the nest it raids.

With postdoctoral scholar Christine Johnson, Herbers introduced two different slave-making species that parasitize the same host species into outdoor enclosures in a field in Ohio. The enclosures had one or the other slave-making species or both at the same time, along with the host species. The researchers then waited to see how the host species did, predicting that the presence of both slave-maker species would be the biggest burden on the host ants. Much to their surprise, the host colonies did better when both parasite species were present together. Johnson and Herbers speculated that the two types of slave makers might have competed with each other, to the detriment of both, leaving the host ants to prosper unmolested. This kind of complicated interaction among several species is becoming increasingly interesting to scientists, since it suggests that we need to look at more than just one