Nectar is a sweet, viscous liquid produced by plants as a reward to attract animals, primarily for reproductive success. This liquid acts as a primary energy source for various insects, birds, and mammals, establishing a fundamental link in many terrestrial ecosystems. The interaction between the plant and the animal that consumes its nectar drives pollination or, in the case of honey bees, the creation of honey.
What Nectar Is and Where It Comes From
The production of this liquid occurs in specialized plant glands called nectaries. These structures secrete a watery solution primarily composed of various sugars. Floral nectaries, located within the flowers, attract pollinators to facilitate the transfer of pollen.
Other nectaries, known as extrafloral nectaries, are situated on non-flower parts, such as leaves, stems, or petioles. The nectar from these structures is not involved in pollination but instead attracts beneficial insects like ants and wasps. These insects consume the nectar and provide a defense mechanism by deterring herbivorous pests.
The Specific Sugars Found in Nectar
Nectar is a mixture of water and sugars, primarily the three carbohydrates: sucrose, glucose, and fructose. Sucrose is a disaccharide, while glucose and fructose are monosaccharides, often called hexose sugars. The total sugar concentration varies widely, ranging from 7% to over 70% by weight, depending on the plant species and environmental conditions.
The relative proportions of these three sugars determine the nectar’s chemical profile. This composition is controlled by the plant to appeal to its target mutualist. The varying ratio of sucrose to hexose sugars influences which animals are attracted to a particular flower.
How Pollinators Influence Nectar Composition
The sugar profile of nectar has evolved to favor the dietary needs and digestive systems of specific pollinator groups. For instance, plants pollinated by long-tongued insects (moths and butterflies) or vertebrates (hummingbirds) tend to produce sucrose-rich nectar. These animals possess the enzymes necessary to efficiently digest the disaccharide and prefer the higher caloric content sucrose provides.
Conversely, plants that rely on short-tongued insects (certain bees and flies) or some bats often secrete nectar dominant in hexose sugars, like glucose and fructose. This specialization ensures the correct animal visits the flower, as the pollinator’s preference for a specific sugar ratio acts as a selective filter. This co-evolutionary adaptation guarantees that the plant’s pollen is transferred by the most efficient partner.
From Nectar Sugar to Honey
Raw nectar collected by honey bees typically contains about 80% water. The transformation of this dilute liquid into thick, shelf-stable honey involves two processing steps performed by the bees. The first step involves enzymatic alteration, where worker bees add the enzyme invertase from a gland in their honey stomach to the collected nectar.
This enzyme begins chemical inversion, breaking the complex sucrose molecule into its two simpler components: glucose and fructose. The second step is the reduction of water content. Bees repeatedly regurgitate and fan the nectar with their wings inside the hive to accelerate moisture evaporation. This process reduces the water content from 80% down to below 20%, which is necessary to prevent fermentation and turn the liquid into the viscous product.