- Category: Science & Technology
April 28, 2009 - Honey bee nectaring on button willow. Photo by Kathy Keatley Garvey.
Gardeners know that plants open and close their flowers at set times during the day. For example, the flowers of catmint open between 6:00 a.m. and 7:00 a.m.; orange hawkweed follows between 7:00am and 8:00am; field marigolds open at 9:00am. In “Philosophia Botanica” (1751), the great taxonomist Carl Linnaeus proposed that it should be possible to plant a floral clock. He noted that two species of daisy, the hawk’s-beard and the hawkbit, opened and closed at their respective times within about a half-hour each day. He suggested planting these daisies along with St. John’s Wort, marigolds, water-lilies and other species in a circle. The rhythmic opening and closing of the plants would be the effective hands of this clock.
Plants have carefully timed routines determined by internally generated rhythms. In 1729, Jean-Jacques d’Ortous de Mairan, a French astronomer, put a Mimosa plant in a cupboard to see what happened when it was kept in the dark. He peeked in at various times, and although the plant was permanently in the dark its leaves still opened and closed rhythmically – it was as though it had its own representation of day and night. The plant’s leaves still drooped during its subjective night and stiffened up during its subjective day. Furthermore, all the leaves moved at the same time. It took another 230 years or so to come up with the term circadian – about a day – to describe these rhythms.
In a similar vein, tobacco plants, stocks and evening primroses release their scent as the sun starts to go down at dusk. These plants attract pollinating moths and night-flying insects. The plants tend to be white or pale. Color vision is difficult under low light, and white best reflects the mainly bluish tinge of evening light.
But plants cannot release their scent in a timely manner simply in response to an environmental cue, like the lowering of the light levels. They need time to produce the oils. To coincide with the appearance of the nocturnal insects, the plant has to anticipate the sunset and produce the scent on a circadian schedule.
Flowers of a given species all produce nectar at about the same time each day, as this increases the chances of cross-pollination. The trick works because pollinators, which in most cases means the honeybee, concentrate foraging on a particular species into a narrow time-window. In effect the honeybee has a daily diary that can include as many as nine appointments — say, 10:00 a.m., lilac; 11:30 a.m., peonies; and so on.
The bees’ time-keeping is accurate to about 20 minutes.
The bee can do this because, like the plants and just about every living creature, it has a circadian clock that is reset daily to run in time with the solar cycle. The bee can effectively consult this clock and “check” off the given time and associate this with a particular event.
Honeybees really are nature’s little treasures. They are a centimeter or so long, their brains are tiny, and a small set of simple rules can explain the sophisticated social behavior that produces the coordinated activity of a hive. They live by sets of instructions that are familiar to computer programmers as subroutines – do this until the stop code, then into the next subroutine, and so on.
These humble little bees have an innate ability to work out the location of a food source from its position in relation to the sun. They do this even on cloudy days by reading the pattern of the polarization of the light, and pass this information to other bees. In the dark of the hive, they transpose the location of a food source in the horizontal plane through the famous “waggle” dance into communication in the vertical plane of the hive.
Honeybees can tell their sisters how far away the food is up to a distance of about 15 kilometers. For good measure, they can also allow for the fact that the sun moves relative to the hive by about 15 degrees an hour and correct for this when they pass on the information. In other words, they have their own built-in global positioning system and a language that enables them to refer to objects and events that are distant in space or time...MORE...
