Adventures Among Ants - Mark W. Moffett [135]
Over the months it became clear to her how enormous and unique the colonies are. Even today, only four colonies are known to live in California: Escondido’s Lake Hodges Colony, two other supercolonies in the southern part of the state, and the Very Large Colony, which controls not only the UCSD campus but also much of the rest of California.
With his stories of supercolony mayhem, described from the curb in Escondido, David had our full attention. Melissa asked how the Argentine ant had become invincible. “Why don’t you visit Argentina with me?” David suggested. “That’s where the Argentine ant comes from. What we’ve learned about Linepithema humile in its home range tells us a lot about how the species has conquered California. It’s stunning.”2
Melissa glanced around at the California ranch houses as we got back into David’s car. Now that, she agreed, sounded more like a proper adventure. “Perhaps,” said David. “But before you leave California, I must show you something.”
BEWARE, LOCAL ECOSYSTEMS
David drove us to the edge of the housing development, where a potpourri of native chaparral plants spread off into the distance. As we hiked past buckwheat, sagebrush, black sage, and laurel sumac, David explained how Californians are accustomed to finding Argentine ants trespassing in their pantries, on their kitchen counters, and in their gardens, where they’re regarded as a nuisance. However, the damage they do is far more insidious. The ants tend to immense numbers of Homoptera—aphids and scale insects—helping them to flourish on backyard roses and in California’s fruit orchards, with severe economic consequences. But it is on the scale of natural ecosystems that their impact is most serious, for they are harbingers of death for many indigenous species. This is especially true for local ants and everything that depends on them.
Argentine ants are as tenacious in the wars they wage with other ant species as they are in battles with their own, annihilating even California ants with far bigger and meaner workers. Though the Argentines can’t sting and are too small to bite humans, they use the energy-rich honeydew from their homopteran herds as fuel to quickly find and dominate every food resource they can reach, thereby leaving the competition hungry. But their depredations go further than that, for even when native species don’t vie for the same resources and offer no physical threat, the Argentine ants plunder their brood for an easy meal.
Some native ant species mount a weak defense. David pointed out a large circular nest mound of seed-harvester ants. They had plugged their entrance in much the same way that Formica block slave raids by Amazon ants. To no avail: the passing columns of Argentine ants would whittle the nest away over time through starvation or repeated assault, giving this native species no chance to proliferate. Even when mature nests manage to hang on, they are, as David put it, “essentially the living dead.”3 The few indigenous ants that survive are able to do so only because they forage underground or come to the surface when it’s too frigid for Argentine ants. All other species that live in the habitats taken over by the Argentine ants have disappeared, their defensive tactics no match for the persistence of the South American conquerors.
The cleansing of indigenous ants has occurred everywhere Argentine ants have spread, namely, to every continent except Antarctica—especially in regions with a Mediterranean or subtropical climate, which include some of the most coveted human real estate on earth, southern California included.4 In each case, the ants form supercolonies, the largest of which extends from Italy to Spain’s Atlantic coast, a distance approaching 2,000 kilometers.
The effects of the Argentine ants’ conquest have only begun to be studied. On the mountain slopes of Hawaii, where