Nectar is a sugar-rich liquid produced by plants. It is produced in glands called nectaries, either within the flowers with which it attracts pollinating animals, or by extrafloral nectaries which provide a nutrient source to animal mutualists, which in turn provide anti-herbivore protection. Common nectar-consuming pollinators include bees, butterflies and moths, hummingbirds and bats. Nectar plays an important role in the foraging economics and overall evolution of nectar-eating species; for example, nectar and its properties are responsible for the differential evolution of the African honey bee, A. m. scutellata and the Western honey bee.
Nectar is an ecologically important item, the sugar source for honey. It is also useful in agriculture and horticulture because the adult stages of some predatory insects feed on nectar such as almost all solitary wasps. In turn, these wasps then hunt agricultural pest insects as food for their young. For example, thread-waisted wasps (genus Ammophila) are known for hunting caterpillars that are destructive to crops.
Nectar secretion increases as the flower is visited by pollinators. After pollination, the nectar is frequently absorbed into the plant. In contrast to floral nectaries, nectar produced outside the flower generally have a defensive function. The nectar attract predatory insects who will eat both the nectar and any plant-eating insects around, thus functioning as 'bodyguards'. Foraging predatory insects show a preference for plants with extrafloral nectaries, particularly some species of ants and wasps which have been observed to directly defend the plants. Among passion flowers, for example, extrafloral nectaries prevent herbivores by attracting ants and deterring two species of butterflies from laying eggs. In many carnivorous plants, extrafloral nectaries are also used to attract insect prey.
Extrafloral nectaries were originally believed to simply be excretory in nature...