America, Argentine ants are known as sugar ants and their colonies are
small. The sugar ants are extremely territorial. If you carry an ant from one
sugar ant nest to a nearby field and drop it into a different sugar ant nest,
the ants in the second nest will kill it.
Frequent seasonal floods have turned these ants into warriors. Every
time the Paraná overflows its banks, sugar ants climb to higher ground,
even into the treetops, to escape drowning. When the waters recede, the
ants must fight to establish the colony’s territory all over again. Over
thousands of generations, repeated territorial battles have shaped the sugar
ant into a lean, mean fighting machine.
Scientists speculate that because these ants are pushed around by
floodwaters so much, they are nomads, moving their nests to different
spots. They aren’t fussy about where they live. Under a rock and a leaf
will do, though they may move several times during the course of a
single day. They aren’t picky eaters, either. While they prefer sugary
honeydew—a secretion that aphids leave behind on plants—the sugar ants
are among the most omnivorous of all ants, eating flower nectar and even
other insects.
In the Paraná flood plain, other native Argentine ant species are the
natural predators that keep the population of the sugar ant in check. But
native ants of North America, Europe, and Asia aren’t able to defeat the
tiny sugar ants. In the United States, they have no natural predators, so
their colonies become enormously big. Argentine ant workers—the ones
who bring food back to the nest—are able to outcompete native ants for
food sources. And in large groups, the Argentine ants tackle and overwhelm
much bigger ants that invade their territory, tearing them limb from limb
from limb. Because the Argentine ants are so aggressive, they dominate the
ant world no matter which continent they call home.
t
he
c
OlOny
as
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uPerOrganIsm
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The most well-studied social insects (those that live in colonies) are ants,
bees, termites, and wasps. Bert Hölldobler of Arizona State University
and E. O. Wilson of Harvard University are experts on the lives of social
insects. They study how social-insect colonies function as superorganisms.
ARGENTINE ANTS 47
