(Ant on Pachycereus, indefenseofplants.com)
Introduction
Extrafloral nectaries are tiny nectar-secreting glands located outside the flower. On leaves, petioles, stipules, or stems, they appear as small dots or raised pads and may feel slightly sticky. Unlike floral nectar, their sugar-rich droplets are not for pollination.
The Details
In many plants, these glands feed ants and other quick patrols, and in return, the visitors chase off caterpillars and leaf-chewers, reducing damage to young pads and leaves. In dry seasons, activity often concentrates on new growth, where protection matters most.
In gardens, if you see ants lined up along leaf margins or bud scales, you may be watching extrafloral nectaries at work. As a rule, avoid spraying; with a strong stream of water, rinse away sooty mold or aphids if they appear, and let the mutualism do the rest.
Additional Reading: Extrafloral Nectaries in Cylindropuntia
Additional Reading: Diversity, Ecology and Evolution of Extrafloral Nectaries
