CICADA KILLERS DON'T STING
week I wrote about the females of an enormous wasp native to the United
States. Known as cicada killers, these wasps do not live in nests; instead,
each female deposits her eggs in the ground on full-grown cicadas that
she has paralyzed and carried to that spot for the developing larvae
to feed on. The males, meanwhile, concern themselves with other activities.
animals, including humans, these wasps have powerful territorial instincts.
A clever study has shown that when boundaries are clearly marked, they
have fewer problems with trespassers. The research findings also illustrate
once again that any animal species, even a lowly insect, can have fascinating
black-and-yellow insects look like they might deliver a serious sting
but are generally harmless to humans - the females because they only
sting people if they are picked up or stepped on; the males because
they do not have stingers.
cicada 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 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 be emerging
from the ground. Upon emergence, the females normally mate with a territorial
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, if a male cicada killer chases you simply stop
and enjoy its antics. Or if you prefer such sport, run, and it will
conducted field experiments with cicada killers to confirm previous
anecdotal reports that naturally occurring landmarks are used by some
species to define territorial boundaries. To test the importance of
visual landmarks in territorial behavior, investigators caught individual
males and painted unique patterns of colored dots on their bodies. After
releasing the insects in a flat, grassy area 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 30 3-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 out of 62 territories had been redefined
within the study area, with the dowels being used as boundary markers.
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 side.
observation revealed an interesting phenomenon 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.
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 boundaries
are distinct, the wasp can be more resourceful.
cicada killers are not more intelligent than politicians in Washington,
D.C., or in Mexico. Nonetheless, they seem to have developed better
coping mechanisms for dealing with the issue of establishing, defending
and respecting boundaries. Maybe there's something to be learned from
these territorial insects by people on both sides of the border.
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