Honey Bee Navigation
A crocus looks very different to a bee. Flowers often have ultraviolet “nectar guides,” which are invisible to humans but aid foraging bees.
Many of us have heard of the amazing ability of honey bees to communicate the location of food and other resources to each other by dancing. The honey bees’ “waggle dance” conveys a wealth of information, including the direction, distance, and the amount of food.
This is even more amazing when we consider honey bee eyesight. A worker bee’s eye is made up of about 4,500 facets, called ommatidia. Each facet sees a small portion of the big picture, so to speak. But honey bees only have about 1% of the eye-to-brain connections that humans have, which means that they see the world at a much lower resolution than we do. Also, unlike human eyes which have receptors for blue, green, and red light, honey bee eyes contain receptors that are sensitive to blue, green, ultraviolet light, and UV polarized light.
Honey bee eyes function in interesting ways. They see flowers differently than humans. They cannot see red, but they can see ultraviolet flower coloration that our eyes cannot detect. Their eyes also have a high flicker-fusion frequency, which means they can easily detect rapidly moving objects. If a honey bee were to view a movie, it would look like a slide show.
The structure and function of honey bee eyes also dramatically affects their navigation. One reason is that honey bees cannot actually see the sun in the sky; at least, not the way we do. Also, to a bee, anything more than about 2 meters away is just a blur. I highly recommend that you check out Andy Giger’s B-EYE, a cool website that allows you to see the world through the eyes of a honey bee (http://andygiger.com/science/beye/beyehome.html).
Honey bees are known to forage many yards or even miles from their hives. Given the limitations of their eyesight, how do they learn all of the information that they communicate to nest mates? Even more concerning, how do they not become lost? Honey bees actually have many navigation tools that they can use: the sun, visual landmarks, and the earth’s electromagnetic field.
If bees cannot “see” the sun, how do they locate it and use it for navigation? One important clue they use is ultraviolet light. Especially on clear days, the bees identify the location of the sun as the area of the sky with the least ultraviolet light. In fact, experiments have shown that a bee may identify any object in the sky as the sun, as long as it is less than 20 degrees across the horizon, and less than 15% of the light associated with it is ultraviolet; the amount of polarization is unimportant. In comparison, a human would identify a 0.4°, completely unpolarized, white circle as the sun, while a bee might identify a 9°, 75% polarized, blue square as the sun. It seems like this would be a problem, but not for a bee.
Relying on the sun for navigation also presents a problem because, not only does the sun move, but its rate of movement changes throughout the day. After foraging for two hours, a bee needs to find her home relative to the sun, but the sun has moved. How does she find her way home? Actually, she relies on experience. Each day the bee memorizes how the sun moves through the sky, and this memory becomes the solution not only to the problem of sun movement, but the problem of cloudy days.
The world as seen through a new imaging system that
mimics honey bee vision.
Another clue from the sun that helps bees navigate on cloudy days is polarized light. The light coming from the sun is actually not polarized, but when it bounces off particles in the atmosphere, it becomes polarized. A bee actually sees concentric circles of polarized light throughout the sky. The bee knows that the strongest polarization lies in a circle that is 90° from the sun, and uses this information to estimate the sun’s location. Patterns of polarized light are so useful that a bee only needs to see one patch of sky that is 10° wide to determine where the sun is.
Although bees have the ability to use UV and polarized light for navigation, they actually rely most heavily on physical landmarks. As long as the landmarks are prominent, nearby (within 2 meters), and unambiguous, a bee will use them as the main source of navigational information. However, they must remain consistent. If the landmarks are moved, the bees will become confused and unable to find the hive.
It is believed that bees have one more navigation tool that is rather remarkable. Even during long stretches of darkness, such as confinement within the hive during winter, the earth’s magnetic field is a reliable means of navigation. The bees are able to detect electromagnetic fields because bees are actually magnetic. They contain a region of magnetite in the front of their abdomens. They also use their ability to detect magnetic fields to regulate their internal clocks and to guide them as they build combs within the hive. If a strong magnet is placed on a hive, with a magnetic field radiating in all directions, the bees will build strange and contorted honey combs.
To summarize, honey bees have four redundant navigation systems that are useful in different situations. Bee learning and memory, as well as the sun, are very important for navigation. The structure and function of their eyes causes limitations, but also provides advantages.
What does all of this mean to beekeepers? Knowing the capabilities and limitations of bee eyesight and navigation can help beekeepers make important management decisions. Where and when to move the hives is probably the most important decision that will be influenced by this knowledge. If you move a hive anywhere from 2 yards to 2 miles, the bees cannot locate previous landmarks, even though for them, the sun’s position and movement patterns have not changed. This causes great confusion for the bees; foragers continue to return to the old landmarks, and many become lost. If bees are moved farther than 2 miles, both the landmarks and the cues provided by the sun change. The bees realize this, and they learn their new surroundings as they forage, preventing confusion and lost bees.
If a beekeeper wants to move a hive more than 2 yards but less than 2 miles, this is best done a little at a time. Alternatively, it can be done during winter, when bees remain in the hive for long periods, because they will naturally reassess their surroundings upon emergence from the hive.
-Cory Stanley, CAPS Coordinator
Gould, J. L, and C. G. Gould. 1988. The Honey Bee. W. H. Freeman and Co., NY. 239 pp.
Gould, J. L., J. L. Kirschvink, and K. S. Deffeyes. 1978. Bees have magnetic remanence. Science 201:1026-1028.