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05/02/2002
Confused Honeybees
I had found a comfort zone of ignorance allowing me to accept
the Big Bang theory, the concept of inflation and even the
possibility that our universe arose out of a random fluctuation of
some sort. Now I see in the newspapers and in a recent issue of
Science that our universe originated when two "branes" bumped
together. Of course, we all know that these branes are three-
dimensional parallel universes contained in an additional multi-
dimensional space. Yeah, right! When confronted with such
mind-boggling stuff like this, I retreat to the experimental world.
While whittling down my huge pile of accumulated journals, I
found in the June 1 2001 issue of Science a reference to just the
sort of experimental work that provides relief from the strain of
trying to understand colliding branes. The experiments involved
honeybees. In particular, these experiments nailed down how the
honeybee measures distance to convey the location of sources of
nectar and pollen to the bees back in the hive.
There we have the queen, a relative handful of male drones and
thousands or even tens of thousands of workers, all infertile
females. To provide food for all these inhabitants and the
material to make honey, the workers who serve as scouts must
find sources of nectar and pollen. These workers then return to
the hive and tell the other workers where the food source is
located and off the forager workers go to harvest it. The scout
conveys the food source location by means of a "dance". If you
have Encarta 97 Encyclopedia on a disc, I strongly recommend
that you go to the honeybee article. If you click on the picture of
the bees doing the dance, you will be rewarded with an excellent
animation and narration showing the dance and its intricacies.
The Austrian Karl von Frisch discovered and studied the nature
of this dance and the way it conveyed the direction and distance
for the foragers to find their way to the source. He received the
Nobel Prize for this work in 1973. His studies spanned well over
half a century and he didn''t just study bees. For example, in
1914 he showed that, contrary to prevailing opinion, fish could
distinguish colors and could smell. Soon after, von Frisch
showed that bees could distinguish colors (except for red).
The format of the bee''s dance depends on the distance of the
source from the hive. If the food is close to the hive, say less
than 50 to a hundred yards away (this figure varies in different
sources), the scout does a "round" dance in which it goes around
in a circle and then goes around in the opposite direction. If the
food source is located farther away, the bee dances a figure 8, the
so-called "waggle" dance. This figure 8 dance has a straight
"run" in it that we''ll see is significant. While the scout does her
dance, other bees join in and also get to sniff and maybe pick up
some of the pollen.
After a round dance, the workers head out from the hive in a
random fashion, knowing the food is nearby and can be located
easily by trial and error. After a waggle dance, however, the
foragers stream out of the hive, the majority headed directly
towards the food source. I presume that some of the workers
don''t quite get the message in the hive and they tend to head off
in the wrong direction. How does the waggle dance work? Von
Frisch found that the straight run in the waggle dance tells the
bees the angle of the source direction to the position of the sun.
He also showed that it could be a cloudy day and that the bees
were still on target as long as there were patches of blue sky. It
turns out the bees use polarized light to find their way and they
don''t have to see the sun itself.
How do the bees know how far to go? Von Frisch showed that
how frequently the scout repeats the dance in a given length of
time indicates the distance. He plotted this frequency of
repetition against distance and found a very nice smooth curve
relating frequency to distance out to 2 miles or so. Von Frisch,
in his autobiography on the Nobel Web site, cites the last of his
most significant works as being published in 1967. He died in
1982.
So, all this has been known for some time. What''s new? One of
the unanswered questions was how does the scout know how far
she''s traveled? Von Frisch and others believed that the scout
knew how much energy it took for her to fly from the source to
the hive. Others thought that the bee was observing landmarks.
Some weren''t convinced that the dance conveyed distance at all,
just direction.
In recent years, these questions have been answered by some
ingenious experiments performed at three universities, Notre
Dame, Australian National and Wurzburg in Germany. The
group leaders there were Harald Esch, Mandyam Srinivasan and
Jurgen Tautz, respectively. How often have you given directions
to someone saying something like "turn left at the gas station;
then go down the road past the church and we''re the third house
on the left after MacDonald''s"? These researchers found the bees
to measure distance in somewhat the same fashion.
Some years ago, the Australian group began experiments in
which they used tunnels. First, they constructed a tunnel near the
hive and placed food in the middle of the tunnel. The tunnels
were painted inside with various patterns that included vertical
stripes. The bees became accustomed to finding food in mid-
tunnel. The food was removed and the bees, as expected,
returned to the middle to look for food. Then a tunnel of smaller
diameter was substituted. The bees flew to the end closest to the
hive. When a tunnel of a larger diameter was substituted, the
bees flew to the end of the tunnel farthest from the hive.
The explanation for this behavior was that the bees judged their
distance by their observations of "flickers" generated by the
patterns as they flew by them in the tunnels. Bees apparently
don''t have good three-dimensional eyesight but are sensitive to
such flickers due to features of the landscape passing by. With
narrower tunnels the patterns flickered by at a more rapid rate
than in the larger tunnels. It''s much like how slowly the scenery
seems to change when viewed from an airplane compared to
when you''re driving at 60 mph on the streets of Manhattan (I
wish!). Hence, the bees think they''ve gone farther and stop
sooner in the narrow tunnels than when they fly through the wide
tunnels. Makes sense.
These studies were followed up by checking the bees'' dance
behaviors. Tunnels of about 20 feet in length were placed within
40 yards of the hive. This was in round dance territory. Sure
enough, when the food was placed at the near end of the tunnel,
the bees round-danced. But, when the food was placed at the far
end of the tunnel, still within round dance range, the bees danced
the waggle. The patterns within the tunnel made the bees think
that they had flown a much larger distance. When the tunnel was
painted with horizontal stripes running the length of the tube
instead with vertical patterns, there wasn''t any flicker and the
bees danced the round dance even when the food was at the far
end of the tunnel.
There remained one more thing to confirm. Did the foragers pay
attention to the misleading dances of the scouts? In the May 31,
2001 issue of Nature, the Australian and Notre Dame groups
described the following experiments. They put the food at the far
end of a vertically patterned tunnel only 11 meters (12 yards) from
the hive. This was so close to the hive that a round dance was
mandated. But no, the scouts danced waggle dances that indicated
that the food was about 72 meters from the hive.
The researchers then took up posts at sites 35, 70 and 140 meters
from the hive and for over two hours recorded the number of
bees visiting the sites. Out of a total of 220 bees, nearly 75% of
them showed up at the 70-meter station, following the 72-meter
instructions from their scouts. Case closed. The bees measure
distance by their perception of what they see and their fellow
bees follow the instructions given them.
After reading the Encarta honeybee article, I couldn''t help
thinking what a strange life these bees have. The queen has a
curved, smooth stinger that she can use repeatedly to dispatch
any rival queens. The workers have barbed stingers that get
anchored in the victim of their sting. As a result the worker
suffers its entrails being ripped out when it flies off and dies
from the loss of said entrails. The drone has no stinger, can''t
feed himself and just lazes around, with workers waiting on him,
while he anticipates having sex with a queen other than his own.
I gather a queen typically entertains advances from a half dozen
or more different drones in an orgy lasting a few days. The
sperm from these suitors is stored in a special sac in her abdomen
where it remains viable for the rest of her 1-3 year life. Her
workers typically live about 6 weeks (more if they''re there over
the winter), while any drones left in the nest get kicked out to die
when fall arrives. You definitely want to be queen if you have a
choice. Of course, her task of laying 1500 or more eggs a day
might be considered a bummer!
Allen F. Bortrum
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