Adventures Among Ants - Mark W. Moffett [86]
A bigger deficit item may be the ants’ nurturing of their homopteran cattle. In the United States, you can locate Formica propinqua ants by the dead cottonwood trees around their nests, which have been sucked dry by the aphids the ants raise.18 In addition, some sap-sucking insects carry infections, making them the plant version of the malaria mosquito. In most situations, though, the cost of Homoptera to trees is not so severe. Azteca, for example, raise sap-sucking insects in moderation on their Cecropia hosts to no evident ill effect. In fact, some trees may have evolved to be tasty to such insects because they attract protective ants, as an alternative to producing nectaries.19
Some of the weaver ant cattle reside not on the trees themselves, however, but on vines in their crowns, which have wide vessels ideal for feeding by Homoptera. Heavy infestations of “plant lice” raised by Oecophylla may in this case inhibit vines from shading a tree or weighing it down and breaking its crown, thus working to the tree’s advantage.20
Overall, weavers are thought to benefit most trees. Could the relation of the ants to choice tree species such as mango and citrus be a rudimentary mutualism, as with Azteca ants and their Cecropia trees, though less precise and obligatory? Researchers have noted of mango and citrus trees that the “odors of the plants may have evolved to attract ants for protection.”21 And the tree wouldn’t be the only one to profit from this arrangement: anything that increases its vigor should benefit the ant colony it houses, by yielding more durable homes and sweet and savory foods—honeydew and prey.22
SPECTACULAR DEFENSES
A few years after my trip to Peru, Dinah Davidson of the University of Utah offered to show me another dominant ant species and impressive adversary of the weaver ant in Brunei, a small, oil-rich country in northern Borneo. After touching down to an evening view of the Sultan Omar Ali Saifuddin Mosque, I arose the next morning for a forest river journey on a canopied boat. Kuala Belalong Field Studies Center was just as I remembered it, solidly built at the base of thickly wooded hills. Dinah, a compact woman with hair cut short for the field, took me up a steep path while pointing out weaver ant territories, which alternated with trees occupied by any of sixteen species of Camponotus carpenter ants belonging to what’s known as the cylindricus group.
The cylindricus ants have dramatic methods of defense. The major worker’s head, for example, is flattened into a disc, enabling her to serve as a living door to nests in hollow branches. She allows her nestmates inside only after they identify themselves by tapping the blockading disc with their antennae (a technique also seen in other ants). Dinah took me to the territory of one of the more unusual cylindricus species and told me to grab a minor worker that was climbing the trunk. I did, and the ant’s leg fell away in my hand, in much the way that a lizard will lose its tail.
Still other cylindricus species exhibit the most extreme behavior of all, employing the “suicide bomber” response to its enemies that I had come to Brunei to see. Wishing me luck, Dinah left me at the base of a tree occupied by one of these colonies and departed. I pulled out my camera, adjusted my flashes, dripped some honey next to the tree from a vial in my pocket, and waited. After an hour, weaver ants along with another species of carpenter ant located the bait and started arriving at the cylindricus-occupied tree. One of them started up the trunk, but then came down again. That one would live another day. Another climbed a bit higher and attempted to walk by a cylindricus minor worker. Just as I clicked the shutter there was a splash of yellow, and both ants were immobilized in a sticky, grotesque tableau.
That picture made my journey halfway around the world worthwhile. Photography is, for me, a tool for storytelling, and this ant’s story left my heart pounding. Approached by an adversary,