An ant inspecting the nectary, a glistening drop of nectar in the middle of it. Smaller nectaries are also present at the end of each serration in young leaves.
Two ant on nectaries.
Tilman, D. (1978). Cherries, Ants and Tent Caterpillars: Timing of Nectar Production in Relation in Relation to Susceptibility of Catepillars to Ant Predation Ecology, 59 (4) DOI: 10.2307/1938771