REVEAL UNUSUAL BEHAVIORS
by Whit Gibbons
July 29, 2007
may not have the political solution to the U.S. immigration problems,
but they definitely demonstrate that the powerful territorial instincts
of many animals are more efficiently managed when boundaries are distinct.
are giant wasps native to the United States. A clever study conducted
on the species several years ago by Perri K. Eason and Gary A. Cobbs of
Northeast Louisiana University and Kristin G. Trinca of the University
of Louisville provided evidence to support the idea that marking boundaries
is the key to preventing trespassing. Their findings with an insect also
provide further evidence that any animal species can have fascinating
both sexes of the black-and-yellow solitary wasps reach lengths of more
than an inch and look like they would deliver a serious sting but are
generally harmless to humans. Rather than living together in a nest, each
female deposits her eggs in the ground on a full-grown cicada that she
has paralyzed and carried to that spot for the developing larvae to feed
killers spend most of their time looking for cicadas. The males spend
their efforts preparing to meet and mate with females. Adult males emerge
from the ground in late summer before the females and set up mating territories,
which they defend against other males. The territories are established
in areas where female cicada killers will also be emerging from the ground.
Upon emergence, the females normally mate with a territorial male, and
presumably the closest one.
killers confront other males who enter their territory. Using intimidation
as their primary weapon, males will sometimes even defend their territory
from other animals, including people who enter the area. Despite their
imposing appearance, the males have no stingers, so if a male cicada killer
chases you simply stop and enjoy its antics. Or if you prefer such sport,
run, and it will chase you.
conducted field experiments with cicada killers to confirm previous anecdotal
reports that naturally occurring landmarks are used by some species to
define the territorial boundaries. To test the importance of visual landmarks
in territorial behavior, the investigators caught individual males and
marked them by painting unique patterns of colored dots on their bodies.
After releasing the insects in a flat, grassy lawn with no obvious landmarks,
they determined by field observations the size and shape of each defended
territory, generally occupied by a single male that was identifiable by
its paint pattern.
then placed thirty, three-foot-long wooden dowels horizontally on the
lawn in a random pattern to serve as tangible landmarks in the otherwise
homogeneous habitat. Upon remapping the territories of the wasps, the
investigators found that by the next day 42 territories had been redefined
within the study area, with the dowels being used as boundaries. And no
male's territory crossed a dowel into the territory of another male, indicating
that these landmarks were observed as the boundaries by males on either
observation revealed an interesting comparison among wasps that were defending
boundaries where a dowel could be used as a landmark on two sides and
where no clear landmark was available on the other two sides. These males
spent more than six times as long during the day defending the sides with
no landmarks as they spent defending the sides where dowels were present
and could be used as landmarks.
In the experiment,
dowels represented natural landmarks. One conclusion offered by the investigators
was that the use of obvious natural landmarks to define territorial boundaries
could have evolved because of the reduction in costs of territorial defense.
That is, establishing a territory in a homogeneous habitat is not energy
efficient for a cicada killer because of the constant patrolling and vigilance
necessary. When the boundaries are distinct, the wasp can be more resourceful.
problems of illegal immigration are in essence a territoriality issue
but more politically complex. Our boundaries are already distinct. Thus,
immigration is readily defined. Our national leaders, who seem either
unwilling or incapable of solving the problem, apparently are grappling
more with what should be viewed as illegal, something cicada killers have
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