Adventures Among Ants - Mark W. Moffett [16]
A marauder ant swarm raid, based on my original drawing, advancing toward the top of the page.
Workers of Proatta butteli seizing a wasp at the Singapore Botanic Gardens.
In Malayan rainforests to the north of Singapore I would later find a second swarm-raiding Pheidologeton species called silenus, closely related to P. diversus but with raids twice as fast, matching the raid speeds of a slow army ant.4 Sluggish or not, the painstaking searches don’t hinder the hunting prowess of these Pheidologeton species, particularly in the diversus marauder ant, which usually takes food in abundance.
I came to believe that there was simply no need for the mass of marauder ants to move along any faster. In fact, in the Botanic Gardens I came upon a different kind of ant nesting at the base of a withered tree that taught me that mass foraging might not require the group to move at all.5 Lumpy beasts with unimpressive jaws, Proatta look incapable of doing anyone harm. Yet that day I saw three workers grab a wasp that must have outweighed them by a factor of fifty; trying to escape, it nearly lifted them all from the ground in an attempt to take flight. Nearby comrades, attracted by the commotion, seized the quarry by the hind legs. Then more nestmates, perhaps drawn to the site from a distance by pheromones, helped to pull the wasp into their nest.
Groups of the same Proatta ants also killed marauder ants that lagged behind on the base trail after a raid. What accounted for their success? While much of their effort is spent scavenging by themselves for all kinds of tidbits, the Proatta workers accumulate in such numbers within inches of their nest entrances that when an insect walks by, several ants are often close enough to pin it down. Proatta essentially stay in place and let prey come to them, using a group version of the ambush tactic employed by a human duck hunter hidden in a blind, or by solitary-living species such as the snapping turtle, which lies in wait for fish to pass by.6
As we have seen, proximity is not essential for ants to act as a group. But the Proatta behavior demonstrates that, as in the packed raids of the marauder and army ants, a high density of participants increases the likelihood that encountered prey will be caught. When their workers are close together, some ant species are even able to avoid active foraging almost entirely. Ants squeeze together inside their nests, and a Mexican Leptogenys species takes advantage of this density by giving their living quarters a scent that attracts the pill bugs on which they feed. The ants jointly kill and feast on these little crustaceans without leaving home.7
But by keeping on the move in a crowded mass, the marauder and army ants accelerate the odds of encountering dinner, compared to these sit-and-wait strategists. It is the difference between dragging a net through water and leaving it fixed in place. Both methods work, but a motile net almost certainly catches more fish during a given period.
ANATOMY OF A RAID
One morning as I watched the foremost workers in a marauder raid nose their way forward through the grass, Paddy leapt up behind me with an insect net. Suddenly the 12-centimeterlong praying mantis he was chasing landed with a shudder within my swarm. Paddy backed away with a mild expletive as the ants overcame the mantis. Some grabbed the wings by their edges and spread them out to their full green glory, while others took its head between their jaws until it cracked open like a nut seized by pliers. Soon the marauders