Many species of treehoppers live in groups. Among the known species, there appear to be 4 mechanisms of benefit to group living: 1) parental care, 2) enhancement of aposematism, 3) host modification, and 4) ant attendance. Group living in treehoppers probably appeared because one or some combination of these mechanisms enhanced the fitnesses of individuals accepting the automatic detriments of group living above the fitnesses of solitary individuals. Experimental evidence for one species, Publilia concava Say, suggests parental care, aposematism, host modification, and ant attendance would select for progressively wider scales of aggregation - from the individual leaf, to the individual plant or stem, to the collection of stems in a stand or patch.