A couple days ago while gathering some giant ragweed (Ambrosia trifida, Asteraceae) with my apprentices, we were attacked and bit by some very uppity ants. Now, ant-insect relationships excite me, and ant-plant relationships even more. Naturally I was intrigued, especially because we don’t usually have biting ants in the southern Appalachians.
Upon closer investigation, I noticed the ants carefully grooming small brown striped insects, which looked like leafhoppers. They also seemed to be carefully guarding egg masses on the midrib of the underside of the leaves. So I set to googling and found that ants will “raise” or “farm” treehoppers (a group of insects in the Membracidae family, which closely resemble leafhoppers) in the same way they will care for aphids. These insects, like aphids, produce honeydew (a sugary exudate produced by leaf sucking insects), which the ants eagerly slurp up. The ants have a vested interest in healthy treehopper populations so they protect the eggs, larvae and honeydew-producing adults. These strong little bodyguards will quickly rise up against weeding gardeners and herbalists alike to protect their miniature “cows”.
Perhaps the ragweed benefits from the ants’ aggressive protection, even if they are raising insects that suck on their juices. Maybe losing a few leaves to the leafhoppers is worth keeping herbivores, which might completely devour a whole plant, at bay. The same day I was taking pictures of elecampagne (Inula helenium, Asteraceae) and I noticed some very active ants on the underside of the leaves. Sure enough, there were treehopper larvae being dutifully tended to by the ants. Elecampagne has been in my gardens for the last twenty years, with this insect mutualism right under my oblivious nose. It just goes to show that one can never poke around on the undersides of leaves enough!