Adventures Among Ants - Mark W. Moffett [36]
When the soil roofs of the arcades sag, the large marauder ants respond to the pressure against their heads as they pass underneath with the shoving technique as well. Captain Charles Thomas Bingham, the Irish officer stationed in Burma, called the majors “the trowels and rammers of the Ant’s Public Works Department.” Their actions raise the drooping arcades and conceivably increase their structural integrity by binding the soil particles. The soil covers are finely granulated on the outside and are smoothed internally by the majors’ battening.
In addition to enclosing their roads, marauder ants build thicker soil edifices over prize fruit or meat bonanzas, structures that facilitate the business of feeding. Workers guard the outer walls while others eat in a narrow gap between this exterior layer and an inner scaffold, which absorbs any moisture in which the diners might otherwise become mired.
Covered-over passages and encased food bonanzas are kept tidiest in areas of dense litter or vegetation that provide physical support so that less caretaking is required to maintain them. To what use is all this effort? Not, it seems, as protection from the elements. The earthworks fall apart in rain, and disintegrate when the earth is dry. Arcades are thin enough to puncture with a tap of a finger, which means a route is weatherproof only when it travels through an underground tunnel, perhaps dug and then abandoned by other animals. Alternatively, near the nest the ants may make a subterranean route of their own: over time, construction crews can scratch away so much soil from the trail surface that the highway sinks from view, at which point the ants seem to be able to construct a thicker, rainproof cover that becomes flush with the surrounding land.
A marauder ant trunk trail with soil sides and partial soil cover, extending through the leaf litter in Johor, Malaysia.
DEFENSE
The main function of this relentless building is defense. Because trunk trails extend for dozens of meters, they travel through territory controlled by other ant species. Marauder ants must therefore be organized to protect the trunk trails from aggressive neighbors or even from hapless passersby such as the Diacamma.
Strangely enough, when the soil ramparts are absent or breeched, the job of defending the trails goes to the most expendable ants in the colony—the maimed and the decrepit. At the spot where I saw the Diacamma killed, a row of minor and small medias stood along either side of the trail, ready to fight off any more of her comrades who might wander by. Marauders darken with age, changing from creamy brown to a dark cocoa color, and I could tell that many of these guards were old from their near-black integuments. Amputees and the infirm struggled to stay upright as they jabbed at additional chance intruders from the Diacamma nest nearby.
Among ants generally, the risks taken by workers tend to increase with age, demonstrating that their long-term value to a colony diminishes as they get older. Months-old fire ants engage in fighting in battles with neighboring colonies, for example, whereas weeks-old workers run away and days-old individuals feign death.7 The old and wounded marauders often serve in the worst occupations, such as trail guards. They also throw garbage from the nest onto the community refuse heap, or midden, where they work until they fall over, their bodies joining the rest of the colony’s waste.
For the marauder colony bothered