Adventures Among Ants - Mark W. Moffett [30]
How does the marauder ant, with its numbers and seeming chaos, nab the wily springtail? Lots of the ants seem to be doing the same thing at once, with sloppy overlap in their activities. But the effectiveness of large societies often has to do with redundancy rather than precision: although an individual ant may not be reliable, the density and overlapping actions of multiple ants ensure success for the raid. As each point on the ground is probed exhaustively, every critter, no matter how small, is rooted out.15 Once flushed, a springtail leaps about as one ant after another frightens it. Sooner or later, one of the minor workers will snare the springtail and make the kill. The raid, in its entirety, becomes the colony’s bear trap.
The effectiveness of this form of predation lies in exhausting the victim. Lions and wild dogs accomplish much the same thing. Although a solitary cheetah may have the edge on them in terms of speed, working as a pack the group predators can kill a gazelle that easily outruns them, wearing it down by chasing it sequentially, like relay runners, or by driving the animal toward an individual lying in wait. Marauder attacks aren’t as subtle or as calculated, but given the ants’ massive numbers, they may not need to be.
THOSE VORACIOUS OMNIVORES
The marauder ants’ predatory skills are only part of the picture. “The voraciousness of these ants is very great,” wrote a Vietnamese phytopathologist named Pham-tu-Thien in 1924. “We are dealing with a species whose greediness has fully developed its capacity for work.” Pham recorded marauder ants consuming insects, seeds, and fruit.16 What they take varies widely according to availability—they nibble on such oddities as leaves, flowers, bird droppings, and fungi when few other resources are available. But even when foods are bounteous, marauder ants tend to be wide-ranging gourmands.
Swarm-raiding army ants, often said to have among the Earth’s broadest diets, don’t compete with marauders in this regard. In particular, army ants are poor vegetarians, while marauders collect equal amounts of plant and animal material. Vegetable matter contains cellulose that many carnivores find indigestible. The only army ant approaching the marauder’s omnivorous diet is south Asia’s Dorylus orientalis, which, like the marauder, is considered an occasional agricultural pest—though it eats tubers such as potatoes, rather than the rice and other grains fancied by the marauder.17
The marauder ant species—Pheidologeton diversus—shows a proficiency at seed harvesting equal to that of many of its seed-harvesting relations in the group to which Pheidologeton belongs, the Myrmicinae, and I imagine the ancestor of Pheidologeton was like many of these relatives in eating seeds while scrounging for dead insects and perchance killing the occasional live one.18 On my Indian palm plantation, instead of taking their seeds straight to the nest as they did prey, the workers established caches along trails, carrying grain down holes or under leaves, where it was stored or milled to an edible flour by medias and majors. The ants also harvested an herb called goatweed by dropping its seeds to the ground, where workers of all sizes congregated to chop them up for immediate consumption.
Marauders are even more organized when they harvest grasses, one of their pastimes in the Singapore Botanic Gardens. When a raid passes a fruiting grass plant, only the minor workers and small medias can climb the slim stalk. The first minors gnaw the attached seeds ineffectually, but productivity skyrockets when a media arrives. The ants now set up a little assembly line, in which the media extracts one seed after another and then appears to hand it to a minor to haul away. What is really happening, however, is that the minor, who is too weak to pull a seed free from the stalk on her own, snatches the seed from the media before the larger ant can depart with it. The media dutifully plucks another seed, which another minor grabs.