When I went out to the garden today, I took a look at the small raised bed I had put together early enough this year that I could grow a few vegetables in it. I planted some fava beans in September and October in the empty spaces, to both act as a cover crop, and to hopefully overwinter and give me some beans early in the spring. They are growing nicely, but as soon as I took a close look at them, I spied trouble. Dark spots were bunched around the stem at the top of one of the plants. I immediately knew what they were. Ants. As I peered closer, I realized they weren’t just ants; they were ants that had taken up farming.
(Down on the ant farm: ants and their quite fat-looking aphid cattle grazing on my fava bean plants.)
This is fascinating insect behavior. Ants will raise aphids like livestock, herding them, tending them, and “milking” them — that is, stroking the aphids to make them produce delicious honeydew…which is basically aphid poo. It’s not as gross as it might sound, because the honeydew is mostly sugar water, as the bugs that produce it live on only sap from plants. (If you still think it sounds gross, then you don’t want to know how bees make honey.) Scientists describe this behavior as mutualistic symbiosis, meaning that both species benefit from the relationship. The ants care for the aphids, and the aphids give them food. I wonder if an intelligent life form from an alien planet looking at humans raising cattle or other ungulates would consider that to be a mutually beneficial situation, too.
The relationship really does seem to mirror a human relationship to livestock. Not only do the ants protect their aphid herds from predators, they also protect them from infection. They defend them even more fiercely from other ant “cattle raiders” than they do from predators. They’ll shelter aphid eggs in their nests over winter and move aphids to new host plants. And apparently, the ants achieve their control over the aphids by drugging them with the chemicals that the ants secrete through their feet and biting the wings off of aphids to prevent them from flying away. Sometimes, they also eat the aphids.
I love that ants are so complex and seem to behave like we do, in spite of how different we are from each other, biologically. I don’t love that it’s happening on my fava bean plants, though. These farming ants have presented me with my own farming problem. The aphids sucking the sap of the plants will damage them, make them vulnerable to disease, and if the farm…um, infestation…gets big enough, prohibit them from growing.
Ants have been the number one pest problem in my garden, so far. They have been a persistent problem in our house, too. Our yard is literally crawling with them. While I don’t relish killing insects, I will use lethal means to stop them from infesting my home. My go-to solution for insect problems in the garden is to spray the plants with a little water mixed with biodegradable dish soap. Sorry, ants and aphids.
At least there’s some salve for my conscience. Ants themselves will kill lacewings and ladybugs that try to prey on their aphid herds. Nature is a harsh mistress, as they say, in the struggle to survive. We may not be able to grow crops without killing some animal pests, but we can do so as judiciously as possible to harm as little as possible.