What, exactly, is nectar?

A bee gleans nectar from a coneflower. — varmfront/Creative Commons

In an era heightened attention to our threatened pollinators, we’re being urged to plant nectar-producing plants to support the birds and the bees. I think everyone knows that nectar is food and consuming it has plant fertilization as a desirable by-product.

When I sit on my screened porch, I’m surrounded by flowers — the lantana and petunias on the back stairs, the phlox and lavender in the garden beds, the verbena in hanging baskets.

I think of them as decorative accents, but that just shows my human bias. A host of nectar-sipping birds and insects think of this setting as an alfresco restaurant with a good vibe and interesting menu.

I have bumblebees, honeybees and wasps of various kinds working the flowers along with monarchs, swallowtails, cabbage whites and other butterflies I can’t identify. Among my favorite insect guests are clear-winged hawk moths that hover at the blossoms like hummingbirds. Levitating on transparent wings, they look like flying shrimp, my pet name for them.

The outdoor dining room also draws ruby-throated hummingbirds that occasionally taste the flowers but prefer the feeders filled with a homemade nectar solution. It must be convincing (and subtly fragrant) since it also attracts wasps and bumblebees, two species that can locate food by smell.

All of this avid eating going on in the flowers just beyond the screens got me thinking — What exactly is nectar? How and why do plants produce it? Does it come in different flavors? The answers turn out to be far from simple.

Nectar is a bribe of sorts, a sweet reward that plants secrete to lure pollinators into the recesses of their blossoms or to rally warrior insects to defend their leaves and fruits from herbivores.

Nature's original soft drink is produced in glands called nectaries by specialized cells that transform plant sap into a fluid with a surprisingly complex composition. There are enough variations in nectars to serve a wide range of tastes — think of the garden as a great big vending machine full of dozens of colas, clear sodas, health drinks and pepper-uppers.

For starters, there are three types of natural sugars in the formula and their ratio varies according to what pollinator the plant hopes to attract. Nectars with a high fructose or glucose content bring in short-tongued bees and flies, while those that are sucrose-rich draw long-tongued sippers like butterflies and hummingbirds.

Hummingbirds are drawn to nectar feeders. — fishhawk/CC

The sugar concentration is important, too. Bees like a syrupy mix with sugar concentrations of up to 50 percent, while birds, bats and butterflies want more liquid nectar with a sugar content of just 15 to 25 percent. It only makes sense — think how hard it would be to suck syrup through a long straw, which is basically what a butterfly's proboscis resembles.

Nectar isn't made of sugar and water alone. The mix can contain antioxidants to short-circuit spoilage, along with proteins, minerals, vitamins and stimulants.

Research shows that honeybees prefer citrus nectars that are naturally spiked with a little caffeine. (Do they get a buzz?) They also favor minuscule amounts of nicotine, contained in the nectars of tobacco plants and linden trees. Neither of these compounds caused ill effects as far as scientists could tell.

It was only recently (in the 1990s) that scientists found at least 60 plant species that have colored nectars — red, yellow, blue-purple and even black. Some of the key research was done on the island of Mauritius off the east coast of Africa. Of geckos that live on the cliff faces there, two-thirds prefer tinted nectar (red or yellow, please).

Plants also advertise their nectar wares with scent, much of it too subtle for human noses.

You don't think of insects as tiny, airborne bloodhounds, but wasps can detect odor molecules in concentrations as small as a few parts per billion. They find the caterpillars in which they lay their eggs by following the scent of chemicals released by plants the caterpillars are eating, another instance of communication via odor.

Wasps may soon be putting their "noses" (actually olfactory sensors on their antennae) to work for the Department of Homeland Security. It turns out you can train a wasp to detect any chemical in about 15 minutes by saturating them with the target odor while feeding them sugar water.

Scientists at the University of Georgia created the Wasp Hound, an odor-detecting device in which the moving parts consist of five captive wasps. Creators figure it has a future in airport security inspections and bomb detection. Cheaper than sniffer dogs, more accurate than electronic "noses," wasps may see their generally bad reputation improve dramatically in coming years.

I'm impressed to know that a sweet tooth — in wasps, bees, birds, bats and lizards — has a place in the natural scheme of things. Think of that the next time you reach for a soda pop, iced tea or fruit drink. Before Pepsi, there was citrus nectar; before Gatorade there was gecko-pleasing red nectar from the Mauritian earring tree.