Since posting my article about ants eating the eggplants here at the Ranch, I've had several notes from others having the same issue, ranging from California to Massachusetts. Apparently this isn't as uncommon a problem as we all thought. Considering the geographical range, I suspect this has more to do with the eggplants than it does with a specific type of ant.
I did get an identification of the ants attacking my eggplants from Carl Olson at the University of Arizona, and he seemed as surprised as I was: "Wow, those ants are Solenopsis, and I am pretty sure they are S. xyloni. The looks can be variable but everything I checked points to xyloni. That is crazy, but they are also such aggressive ants when they find food resources."
Solenopsis xyloni is the common Desert Fire Ant, a native to this region and throughout the Southern United States, including California.
So, we know what kind of ant, but now what?
Well, an interesting thing happened here at the Ranch: the ants kept eating the eggplant, but the eggplant, it turned out, didn't seem to mind. I still have a bumper crop of eggplant.
When I first noticed the ants, they were cutting into stems at the terminal growth and in the leaf axils. They seemed not so much to be eating the plant tissue, as they were opening areas to eat the plant "juices," the sap. A fine distinction, perhaps, but as it turns out an important one.
The destruction and cutting of stems was secondary to the ants' activity. Ants, almost by definition, are extremely organized and industrious workers. Had they been setting out to cut and harvest plant stems and tissue, the plants would have been gone in no time. Once ants have their collective mind set to a task, that task gets done.
Instead, the ants were sipping plant juice, so any terminal or flower growth not in their immediate "grazing ground" continued to grow unmolested. Hence my bumper crop of eggplant. I am up to my ears in eggplant.
There's an important gardening and pest-management principle here, and one I've said before: insects are only a problem when they cause damage at an unacceptable level. If our goal is, for instance, to harvest eggplant, then as long as we're harvesting eggplant we don't need to worry about the ants.
For those of you who wrote to me about similar eggplant and ant issues, take a look to see if you're still getting fruit. I'd be interested to hear if your experience is turning out the same.
I hope this helps,