Adventures Among Ants - Mark W. Moffett [140]
Argentine ants employ these exploratory patterns in order to muster a concentration of workers everywhere at once. They may not attain the aggregate densities and strength of raging army ants packed in a raid, or show the multipronged communication systems of the weaver ants, but the race is not to the swift, nor is the battle to the strong. The Argentine ants turn out to succeed despite a lack of many of the organizational skills we have come to expect from large societies in this book. The workers show a minimal division of labor, without polymorphism. They do not have assembly lines and teams, and they are not adept at moving food in a group (nor do they need to, since theft from competitors is so unlikely that they can eat the food where they find it). Yet they take to phenomenal extremes the rapid dominance military practices deployed by the marauder ant. Like a starfish that succeeds in prying open a clam through persistent application of pressure, these ordinary-looking imperialists wear down nasty rivals and prey many times their weight in wars of attrition staged over hours, days, weeks, and even years.23
17 the immortal society
In 1997 chemists Dangsheng Liang and Jules Silverman, working for Clorox, a company that makes baits for ants and cockroaches, were raising both kinds of insect in the laboratory. When their practical technician decided to feed their stock of Argentine ants a diet of the roaches on hand, what ensued was an example of scientific serendipity that parallels Jill Shanahand’s discovery of Argentine ant warfare. At first, the ants happily ate their new food source. But then, as Dangsheng wrote me, “One day we noticed that instead of eating the roaches, the [ants] were trying to kill each other. Then we found out that the technician had switched the species of cockroaches he fed the ants, from German cockroaches to brownbanded cockroaches, which he had lots of that day.” Within the hour the container was littered with dead ants.1
It turns out that Argentine ants will set upon any group of nestmates that has been in contact with a Supella longipalpa, or brownbanded cockroach, a pest introduced to the eastern United States from West Africa. The contaminated ants do not fight back because they still recognize their attackers as colonymates. But over the subsequent weeks, the surviving outcasts form their own group—essentially, a new society.
A society has been described as “a group of individuals” that is “organized in a cooperative manner.”2 But this description is incomplete: to create a stable, cooperative society, the members must also identify as a group, and to do so, they must see each other as similar and outsiders as different. To accomplish this, the members generate and recognize “labels”—shared signs of their identity, such as a common language or national flag for humans.3 Hydrocarbon molecules on the body surface, detected as scents, are the labels ants use to form their societies, and individuals lacking the right ones may be ruthlessly killed. Dangsheng and Jules immediately understood that the exoskeleton of a brownbanded roach, perhaps by coincidence, has some critical component of the scent that Argentine ants use to cue in on one another. Contact with a roach transferred these hydrocarbons and caused the ants to be misidentified as belonging to an enemy colony.4
While confusing the scent of one colony with that of another can be a disaster, acquiring the right odor is like being given the key to a city: all is possible. In an orchard in Daintree, Australia, I tore apart a weaver ant nest to find an orange arachnid 5 millimeters long marked with clean white stripes. I recognized the species through the pain of the ant bites: Cosmophasis bitaeniata, a jumping spider that joins a weaver ant colony as if it were an ant itself. This identity theft is achieved when the spider takes on the colony’s aroma by stealing and eating brood, after which it