Nectaries

Flowering plants attract honey bees and other pollinators as a method of moving pollen within and among flowers to reproduce the plants. To attract the pollinators, plants emit fragrances, display colorful flowers with intricate shapes, and offer tasty and nutritious foods. The foods are carbohydrates from nectar and proteins, fats, vitamins, and minerals from pollen. Nectar is usually secreted by the flowers. Honey bees are directed to the nectary, the nectar-bearing part of the flower, by ultraviolet nectar guides. The nectary is usually located in the center of the flower. However, nectar is secreted by some plants in areas outside of the flowers. Among the plants with extra-floral nectaries is the catalpa tree, which is now in bloom. Today, I watched a Baltimore oriole feeding on nectar in catalpa flowers. Honey bees were flying into the large bell-shaped white catalpa flowers, and they were also working extra-floral nectaries on the large catalpa leaves. The leaves secrete sugary nectar to attract pollinators like the bees in today’s photo. Catalpa trees are members of the trumpet creeper family. After pollination, catalpa produces wind-dispersed seeds that hang in long pods.

Cotton is another flowering plant that secretes large amounts of nectar outside of the flower. After the first day’s bloom, which yields nectar from the blossom, cotton secretes nectar from bracts, leaf-like parts outside of the flower, and from leaves. Other plants have flowers that make it difficult for some pollinators to access the nectary. Honeysuckle flowers have a long bell-shaped flower making it difficult for honey bee tongues to reach the nectar. However, honey bees can access honeysuckle nectar after leaf-cutting bees chew through the side of the flower. Honey bees follow leaf-cutting bees to forage on hosta lilies as well. To access the nectar of alfalfa, honey bees must trip a trigger in the flower which delivers an annoying slap in the bee’s face. The foraging techniques used by honey bees to access the nectar of different plants are learned behaviors.

--Richard