ARE INTRIGUING CREATURES
by Whit Gibbons
September 17, 2006
fire ants, but no one is likely to suggest that ants are not intriguing
little creatures that constantly amaze us. The more ants are studied,
the more they reveal capabilities that exceed their small size.
army ants have been said to comprise “the most cohesive societies
on earth" because of their incredible cooperative behavior, such
as the remarkable feat that occurs when they face a stream. To cross the
water, the workers lock legs to form an ant-bridge of bodies for the others
to walk on. Army ant colonies operate in many other ways like single organisms
with a plan, like a problem-solving unit responding with a collective
intelligence to special situations. Colonial bees, ants, and wasps function
as individuals in the best interest of the colony. That’s why they
sting us. Many mysteries remain about army ants, such as how they decide
which direction the raiding colony will go each day.
how animals navigate has been of long-standing interest to behavioral
scientists. This past year, Matthias Wittlinger and Harald Wolf of the
University of Ulm and Rüdiger Wehner of the University of Zurich
conducted investigations that to me were as intriguing as the ants themselves.
They put stilts on the legs of ants to find out how they found they way
home after a long trip.
desert ants forage, they return home in a straight line, though their
route in search of food may have been a winding, circuitous one across
flat desert with no visible landmarks. Based on earlier studies, the ants
are known to use a directional compass involving the sun for orientation.
Proper navigation also relies on a heretofore unknown mechanism for measuring
the distance traveled in various directions. Even in the dark the ants
are able to assess how far they have walked.
advanced many years ago is that ants somehow measure distance traveled
by registering their leg movements. That is, by counting how many steps
they have taken. To test the hypothesis the scientists conducted experiments
in which ants were trained to follow a channel over sand to a food source.
The top of the channel was open so that the ants were able to obtain compass
information from the sky. The channel was about ten yards long, and upon
reaching the food, experimental ants were captured and prepared for the
The ants were released to return home in another test channel that was
parallel to the one they traveled from home. This assured they that did
not use chemical cues from their previous route to find their way home,
but they could still see the sky and keep their sun-compass orientation.
But, before the ants were set on their way home, the researchers attached
stilts (made from pig bristles) to an ant's legs to lengthen its gait.
Or they shortened the ant's legs by literally cutting off the lower part
of each leg. This apparently did not much bother any of the ants, because
after its orthopedic surgery, each ant took some food and headed home.
on the trip home, ants with stilts took longer strides, and those with
shortened legs took shorter ones than they had taken on the trip out.
And sure enough, the ants with stilts walked beyond the point where they
thought their home site would be whereas the ants with shortened legs
did not go far enough. In other words, they were not using sight or smell
to find their home but were counting how many steps they would have to
take to return to it. In a separate experiment ants were outfitted with
stilts or short legs before they began their ten-yard walk to the feeder,
so that they had the same stride length in the outbound and homebound
trip. This time the ants accurately assessed the homing distance on their
concluded that the ants measured the distance traveled by some mechanism
whereby they count the number of steps taken, allowing them to navigate
by integrating how far they have traveled in different directions. Ants
are indeed intriguing, and so are scientists in figuring out unusual ways
to study them.
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