Ant and Leafhopper Symbiotic interactions

Goldenrod plant stems are hosting this thorn-shaped leaf hopper and it is being "tended" by a species of tiny black ant. This interaction of two ants per leafhopper was observed on one other occasion in the same meadow on a distant plant stem. The ants stayed with the hopper in this case. Observatinos mid-day very warm day. I observed no predation, just ants touching their antennae to the hopper body and sitting on it for an extended period of time, resting near the hopper in both separate cases.