Adventures Among Ants - Mark W. Moffett [136]
Even some vertebrates have been disappearing from coastal southern California, thanks to the Argentines. Horned lizards, shaped like thorny pancakes, require a balanced diet of diverse native ants, whereas the Argentine ants are themselves too small and quick for the horned lizards to catch. Adding insult to injury, the Argentine workers are experts at harassment, literally driving the reptiles into the sand.7
Argentine ants feeding on a protea seed in the fynbos habitat of the Western Cape of South Africa.
The best-documented effects of Argentine ants on plants are in the fynbos, a Mediterranean-like ecosystem in South Africa. Here, the original ant fauna is pivotal in seed dispersal, as I saw in 1996 on a visit to these vibrantly colored heathlands with Cape Town myrmecologist Hamish Robertson. Beneath the blood red flower stalks of one of the resident proteas, Hamish showed me native Anoplolepis custodiens ants that were hauling the plants’ seeds to their nest, where the workers would eat outgrowths on the seeds called elaiosomes. Afterward, the discarded seeds, like those of hundreds of other local plants, would have a chance to sprout in the ants’ nutrient-rich trash heap. A short drive away, an encroaching Argentine ant supercolony had taken over a different area, wiping out the Anoplolepis. There, we found the ants eating the elaiosomes in the open but leaving the heavy seeds behind to dry out and die.8
The native plants of southern California face a similar threat. A small tree called the California bush poppy, which David pointed out on our visit to the besieged harvester ant colony, depends on the vanishing harvesters to carry off its hefty seeds.9 This is only one of many native California species in decline in the areas encroached on by the Argentine ant. The result is that the flora and fauna of California and other affected regions are becoming increasingly uniform, in a tragic process known as biotic homogenization. In this battle, we are all the losers.
A DESTROYER ABROAD, BUT JUST ANOTHER BRUISER AT HOME
A year later, Melissa and I found ourselves shaking hands with David Holway again, this time in the stifling early morning heat of the Corrientes bus station in northern Argentina. We had just arrived from Buenos Aires, where the steaks were immense and I had managed a tango lesson without injuring either Melissa or the tiny but stern dance instructor. Still groggy from thirteen hours on a bus, we climbed into David’s tin can rental car with his former student Ed LeBrun and drove another three hours to the field site. Relieved to finally stretch our legs, Melissa and I tromped with David and Ed through a thorny pastureland along a river, watching out for stray bulls. At our feet meandered thin columns of Argentine ants.
The discovery that California’s Argentine ants join forces to create supercolonies had piqued David’s curiosity as a postdoctoral student at UCSD. Was this ant, clearly an outrageously proficient fighter in California, as murderous in its native country? With this question in mind, in 1997 David and three colleagues had headed to the region Melissa and I were now visiting, where the species demonstrates its preference for moisture by living in river floodplains.
To the researchers’ surprise, the Argentine ant is nondescript in its indigenous land, so innocuous and with the workers so sparsely distributed that the locals know it as the “sugar ant” (after one of its favorite foods) and hardly give it a glance. Moreover, workers transplanted between nearby nests often fight one another, suggesting the colonies are many