Population dynamics of colonies of the mymecophilous leafhopper Dalbulus quinquenotatus DeLong & Nault were recorded in the laboratory in the presence and absence of the tending ant, Formica fusca (L.). These experiments used colonies of leafhoppers started with five male and five female adults on a single Tripsacum dactyloides L. plant. The first experiment consisted of eight leafhopper colonies, four with tending ants and four without. The second experiment used 16 leafhopper colonies, eight with tending ants and eight without, with four of each of these ant treatments also with Nabis americoferus Carayon predators. The numbers of young nymphs, older nymphs, and adult leafhoppers, along with host plant condition were recorded every 2–3 d for 62 d for both experiments. Nontended leafhopper colonies exploded and overwhelmed their host plants, killing them in an average of 39.0 d, resulting in the extirpation of those leafhopper colonies. Ants maintained leafhopper colonies by regulating population dynamics, with colonies of leafhoppers tended by ants being significantly smaller (P < 0.02) and developing from egg to adult significantly slower (P < 0.001) than colonies of nontended leafhoppers. Ant-tended leafhopper colonies did not overwhelm their host plants during either experiment, as the ants removed excess honeydew and leafhopper exuvia, thus maintaining a constant supply of honeydew. Ants were observed protecting leafhoppers from nabid predators, although this protection did not significantly influence leafhopper population size or length of egg to adult development.