Adventures Among Ants - Mark W. Moffett [87]
A Brazilian ant I’ve yet to see, Forelius pusillus, has an equally fatal approach to protecting the nest. Up to eight sacrificial individuals stay outside at night to seal the entrance with sand, kicking the final grains in place until no trace of the hole is visible. Walled off from their sisters, by dawn almost all are dead, for reasons unknown—perhaps the squad consists of the old or sick. The ants in the nest then clear the passage to begin the day’s foraging. That night, more victims seal the door.24 No one can say what prompts this preemptive defense, though dangerous army ants would be one safe bet.
A Camponotus cylindricus–group ”exploding ant” has ruptured her body to spew a sticky yellow glue, which has killed both her and the larger worker of another species of carpenter ant in Brunei, Borneo.
In northern Borneo, cylindricus often jointly control their canopy territories with certain Polyrhachis, which have their own self-destructive defense. The first time I saw a gleaming gold specimen of one big, attractive species of this genus, I couldn’t resist touching her—and immediately had the worker embedded in my finger and unable to remove herself, thanks to the fishhook-shaped spines on her back. Birds and lizards must learn to avoid these pincushions.
DOMINANCE AND SUBORDINATION
If these colonies are viewed as organisms, a worker’s death is of no more consequence than a man cutting his finger. The larger the colony, the less consequential the casualty. Extremist defenses, then, are a manifestation of a large labor force. Such extremism in handling risk is an example of how death without reproduction can be of service to queen and colony, and a reminder that anything humans concoct—even suicide missions and terrorism—probably has a parallel in nature.
Just as trained armies and impersonalized warfare came into being among people as populations exploded with the development of city-states, inexorable, large-scale offensive and defensive conflicts between rival ant nests usually involve the numerically dominant species, with their huge colonies. One likely reason is that the necessary communications are best orchestrated in large societies, whether they involve written languages in humans or pheromones in ants. Another reason is simple efficiency. Larger human settlements have higher per capita productivity, with fewer resources required to feed and house each individual.25 This pattern, if similar among ants—which remains controversial26—may enable large societies to more easily accrue the spare time, energy, and resources that can be invested in creative endeavors (by people) and armies (by both ants and people). As a result, not only are the ants of large societies more expendable individually, but the group as a whole may also be able to take more large-scale risks, given that losing 10 percent of an army will be more devastating for a society of ten than for one of a million.27
Yet another advantage of community size is that populous societies control large spaces, and large spaces have relatively small perimeters (a large circle, for example, has a smaller circumference relative to its area than a small one). Thus, the bigger a colony, the smaller the proportion of its population that needs to be employed in border surveillance, and the more troops it has free to commit to offensive battles.
Ecologically dominant species are usually too competitive to coexist. On occasion there is a détente between two of them based on different nutrient and housing needs, as with the antgarden ants, which eat different-sized prey, or the Polyrhachis species that share territories with the exploding ants. Polyrhachis nest on the ground and eat honeydew and insects, while cylindricus nest in trees and specialize in licking the microbial film growing on foliage.28 Even with a large labor force, it pays to be selective