Adopting the enemy
If the army ants are more housewives stocking their larder than noble soldiers proving their mettle, what about the slave-making ants with their “wonderful” instinct, as noted by Darwin? The wars, or raids, that these ants undertake are not about getting food, at least not directly. A slave-maker colony is started when an inseminated queen of one species enters the nest of another, kills or expels the resident queen or queens, and begins to lay eggs of her own kind. Her children are then reared by the host species, which accepts them as if they were nestmates. To replenish the host workers, the slave-maker species sets out on periodic expeditions to snatch the larvae and pupae from another host colony, bearing them back to the slave-maker nest to mature and act as normal workers for their hosts. About 50 of the 11,000 known ant species behave in this manner, with some capable of living on their own and others so specialized that they cannot even feed themselves without the help of their captives.
Despite their rarity, the slave-making ants have attracted a great deal of human attention. Charlotte Sleigh documents the fascination of 19th century observers with the slave-making ants, many of whom were quite overt in their analogy with the human slave trade of the time. Perhaps surprisingly, many naturalists and authors decried, not the practice of exploiting the labor of others, but the “degeneracy” of the slave-makers themselves. In characteristically opinionated prose, Maeterlinck disapprovingly notes that the slave-makers “cannot eat without assistance, for they cannot take any nourishment save from the mouths of their servants. They are as little capable of rearing their young as of building or repairing their nest. In the depths of their lair they pass their time in besotted idleness, rousing themselves only in order to polish their armor, or to pester their slaves for a mouthful of honey. Without their servants these magnificent warriors, with their bronze armor, these superb shock-battalions, these irresistible veterans of great campaigns, are as impotent, as utterly helpless as so many suckling infants.” In his 1954 book Ways of the Ant, John Crompton was similarly censorious: “Even if their slaves do not desert them, mental and physical decay will in itself and in its own time exterminate them. There must be many species of slave-making ants that have died out for this reason.”
Although his language is rather histrionic, Maeterlinck was scientifically accurate, at least with regard to the obligate slave-making ants; in the early 1800s the great entomologist Pierre Huber had placed a group of ants of one of the slave-maker species in a kind of ant farm, along with honey to eat and some of their own pupae and larvae. Within a few days half had already died and the remainder was on the brink of starvation.
The raids themselves can be quite dramatic to witness. The species whose brood is being taken generally attempt to drag the pale, helpless larvae and pupae away from the nest, only to be pursued by the workers of the host ant species. Raids seem to be confined to certain times of the year, and at least some of the ants studied in this regard use cues from within the nest to decide when to begin raiding behavior. Slave-making in ants is confined to temperate regions of the world, and scientists have suggested that the absence of seasons in the tropics explains the lack of raiding and hence slave-making behavior, since there is no internal signal that indicates when pupae can reliably be abducted from their nests. Some species also raid at certain times of day. Joan Herbers, a scientist at Ohio State University and an authority on such ants, says that when she was at Colorado State University her students knew exactly when to go looking for raids: “Jeremy [her student] could head to the hills of Colorado around 10 in the morning, knowing he would be done with fieldwork by 3 or 4.” Others are not so reliable: “We have set up many experiments in the lab; some days they raid and other days they don’t. Some days they raid fiercely and other days the raids fade away. Sometimes it takes an hour and other times 6-8. It’s a pain, and has frustrated several journalists who have visited my lab.”
In addition to studying the ants as a scientist, Herbers has questioned the wisdom and accuracy of the name “slave-maker ants.” She is not alone in this regard; Hölldobler and Wilson point out, “It is traditional to use the expression “slavery” for the exploitation of one species by another. In the human sense this is not slavery but more akin to the forcible domestication of dogs and cattle by humans.” They go on to detail situations in which ants use the labor of others from the same species, but the term “slavery” is clearly limited in its applicability. Some entomologists use the more technical jargon term “dulosis” to refer to the process, whether within or across species, but most scientific journals still call it slave-making.
Herbers isn’t just concerned about the use of the word slavery by scientists. She questions its suitability given its obvious connotations of human activity. At public lectures, she often is asked about the parallel between ant and human slavery, a parallel she always decries. She has come to the conclusion that we would all be better off abandoning the metaphor and terminology entirely, because of its emotionally loaded overtones. “How,” she writes, “can we (overwhelmingly white) scientists casually talk about slavemaking ants, with implicit messages of power, inequity, and subjugation, without recognizing that our very language is a powerful deterrent to recruiting descendents of slaves to appreciate our scientific work?”
As an alternative, Herbers proposes the term “pirate ant,” since human pirates also make raids and steal cargo, often killing some of the victim ship’s crew. Scientists could continue to discuss raiding parties, captives, and booty, without recourse to the loaded terms that certainly bring the public up short.
The reaction from scientists to her suggestion has been lukewarm at best, although many recognize the social biases she identifies. Myrmecologist and blogger James Trager wasn’t quite satisfied with the pirate substitution, and also finds dulosis etymologically inaccurate. He proposed calling the behavior cleptergy, which should correspond to “theft of work or workers,” since “ergates” means “worker” or “laborer” in New Testament Greek. Admittedly, it has a masculine gender, which causes a puzzle of its own if it is to be applied to ants. Whose terminology catches on remains to be seen. I am in agreement with the distaste for the word slavery in non-humans, and use it here only when the original authors use the term, so as not to rewrite their usage.
Reprinted from Sex on Six Legs: Lessons on Life, Love, and Language from the Insect World, by Marlene Zuk © 2011 by Marlene Zuk. Used with permission of the publisher, Houghton Mifflin Harcourt.