Daniel J. C. Kronauer - Army Ants: Nature’s Ultimate Social Hunters

The air is hot and humid, and mosquitoes are buzzing around my head. As I walk along a muddy path through the tropical rainforest of La Selva Biological Station in Costa Rica, the giant trees with their enormous buttress roots groan under the heavy load of strangler figs, lianas, epiphytic ferns, and bromeliads ( ). Besides the humming pests and the sighing trees, everything appears quiet and peaceful. But suddenly a group of birds hop around on the forest floor and in the low vegetation, chirping busily. The birds are so focused on whats going on beneath them that they dont seem to notice as I get closer. They are after a rustling wave of cockroaches, crickets, scorpions, and spiders that scurry through the leaf litter. Yet the birds are not the only ones taking advantage of this curious stampede, as scores of parasitic flies dart down to deposit their eggs or larvae on the unfortunate fugitives.

The insects and spiders have been forced into the open because they are running from what might be the ultimate arthropod nightmare. Like a dark shadow cast on the forest floor, a raiding party of Eciton burchelliiarmy ants, hundreds of thousands of individuals strong, is moving across on a daily hunt. The ants form a carpet-like swarm, 10 to 15 meters wide and 2 meters deep, attacking everything that fails to escape. The colonies of social insects, mostly those of other ants, are overrun and their brood chambers plundered. Big arthropods, each vastly larger than the individual army ants, are overpowered by the sheer number of attackers; they are pinned down, stung, and severed into smaller pieces that the ants deem suitable for transport ( ).

FIGURE P.1A muddy path leads through the tropical lowland rainforest at La Selva Biological Station in Costa Rica. The forest is home to an astonishing number of plant and animal species, including several species of army ants.

FIGURE P.2Army ants overpower large prey by their sheer numbers. Here, a roach falls victim to anEciton burchelliiswarm raid. Alta Floresta, Mato Grosso, Brazil.