When's lunch? That's the blooming question!

By Gary Raham
Nature Writer and Illustrator

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With spring approaching, the flowering world seems poised to entertain humans with a delightful succession of colors and smells.

I always look forward to the first pasque flowers, their pale blue cups and hairy stems outlined in the morning sun. They are followed by a host of summer-blossoming forms that seem to burst like rapidly warming kernels of popcorn. Late "poppers" include plants like showy stonecrop (Sedum) that bloom late summer into fall.

Flowers also possess daily rhythms for blooming. Two hundred years ago Carolus Linnaeus, the inventor of scientific nomenclature, observed that you could literally use flowers as clocks to know what time it is. Goatsbeard (Tragopogon) opens its flowers from 3 to 5 a.m. and closes them by 10 a.m. Your neighborhood dandelion opens for business from 8 to 10 a.m. Other flowering plants specialize in night blooming, like a climbing cactus called Selenicereus grandiflorus, or "Queen of the Night," whose flowers don't open fully until midnight and then quickly wilt at dawn.

Human beings act as voyeurs, merely admiring these blooming displays. But as we all know from "birds and bees" lectures, plants trade high food value nectar and pollen for help with their sex lives. So pollinators like honeybees avidly read these floral timepieces for their very survival--paying as close attention to them as we might to Safeway's opening and closing times.

Like all smart shoppers, honeybees look for food that is cheap, abundant, and of high quality. They may even forsake their usual "grocery store" when a bargain turns up elsewhere, as the Swiss psychiatrist and entomologist, Auguste Ford, discovered one summer in 1906.

Ford's family had the habit of having breakfast on their open-air veranda. He wrote: "In the morning, from 7:30 to 9:30 or 10:00, preserves are provided, which remain upon the table, for, the children going to school at an early hour and the elders rising late, breakfast is a moveable feast." One morning bees discovered the preserves. From then on, they would appear in swarms right on cue in time for breakfast--even when Ford gave instructions "to put the table as usual on the terrace next day, but not put any preserves thereon."

But flowering plants have been advertising for insect, mammal and bird pollinators for at least 120 million years, and they have become quite good at it. The quality and quantity of the product they offer does vary in a cyclical manner, however. The sugar content of nectar rises and falls during the day. Careful pollinating shoppers will find the best quality nectar at midday, even from flowers that secrete nectar mostly in the morning or evening. In general, nectar is sweeter when the sun is shining, the temperature is increasing and the humidity is decreasing.

Quantity of nectar produced by flowers can vary from 1 to 5 milligrams per flower per day. Sometimes quality and quantity peak at the same time; other times quality remains pretty constant, but the amount of nectar produced goes through one or more maxima; and for some flowering plants the amount of nectar stays pretty constant, but quality varies. Pollen displays similar variations, with quality and quantity tending to peak in the morning hours.

As you can imagine, it pays for pollinators to have a good memory. Leave it to curious scientists to test the nature of that memory.

Max Renner, a student of the German animal behaviorist Karl von Frisch, asked himself: Is the bee ruled by an internal, circadian rhythm independent of outside influences, or does she entrain herself to the sun or other external stimuli that might include social interaction? As you might suspect, the answer turned out to be fascinatingly complex.

Renner found, as Ford had observed, that bees could be trained to feed at certain times of day by offering them tasty sugar water. He trained Paris bees to eat between 8:15 and 10:15 in the morning, then he flew them to New York overnight and kept them indoors, away from environmental cues, at constant lighting and temperature conditions. Sure enough, they turned out at the feeding dishes at 3 p.m. EST, 24 hours after their last meal in France.

Part two of the experiment highlighted some nuances of the behavior. Renner trained bees in an open field in Long Island, N.Y. He then flew these bees overnight to a plowed field in the Sacramento Valley of California, displacing them exactly 48 degrees of longitude. This time, the bees showed up twice for feeding: once, 24 hours after their last feeding in New York, and once an hour and a half later--the local time equivalent of their last feeding. It took the bees three days to get over their jet lag and synchronize cycles.

Part three of the studies showed that time-trained bees also quickly adapted to social cues from hivemates in a different location that fed on another schedule. Such bees showed up to eat three times: 24 hours after their last feeding; at the jet-lag displacement time; and when the local bees said it was chow time. Again, in about three days, the honeybees got all their clocks synchronized.

So why don't plants keep the cafeteria open all the time? For one thing, producing nectar and pollen costs energy which plants, like all creatures, must conserve. Secondly, in a flower-beat-flower world, you can sometimes end-run the competition by flowering when the other guy isn't, both on a daily and annual basis. This ties in with pollinator behavior, of course. Moths and bats visit night bloomers. Spring bloomers may cater to the first bumblebees that warm with the season.

Annual variation in blooming accomplishes something else: It extends food availability for a longer time, giving pollinators a greater opportunity to mate and raise their young. While many pollinators show brand loyalty to certain flowers, they will be flexible when that brand is no longer available.

Consider that the next time you are on the patio spreading jam on your toast, getting ready for another day earning the money to spend at Safeway.

Gary Raham of Wellington writes and illustrates science books and articles for children and adults. His most recent book, "Teaching Science Fact with Science Fiction," will be released by Teacher Ideas Press sometime this year.