The Great Imposters

Finding good day
care can certainly pose a problem these days,
unless, of course, you\'re an African widow bird.
When it comes time for a female widow bird to lay
her eggs, she simply locates the nest of a nearby
Estrildid finch and surreptitiously drops the eggs
inside. That\'s the last the widow bird ever sees of
her offspring. But not to worry, because the
Estrildid finch will take devoted care of the
abandoned birds as if they were her own. And
who\'s to tell the difference? Though adult widow
birds and Estrildid finches don\'t look at all alike,
their eggs do. Not only that, baby widow birds are
dead ringers for Estrildid finch chicks, both having
the same colouration and markings. They even act
and sound the same, thus ensuring that the widow
bird nestlings can grow up among their alien
nestmates with no risk of being rejected by their
foster parents. MASTERS OF DISGUISE Things
aren\'t always as they seem, and nowhere is this
more true than in nature, where dozens of animals
(and plants) spend their time masquerading as
others. So clever are their disguises that you\'ve
probably never known you were being fooled by
spiders impersonating ants, squirrels that look like
shrews, worms copying sea anemones, and
roaches imitating ladybugs. There are even animals
that look like themselves, which can also be a
form of impersonation. The phenomenon of
mimicry, as it\'s called by biologists, was first noted
in the mid-1800s by an English naturalist, Henry
W. Bates. Watching butterflies in the forests of
Brazil, Bates discovered that many members of
the Peridae butterfly family did not look anything
like their closest relatives. Instead they bore a
striking resemblance to members of the
Heliconiidae butterfly family. Upon closer
inspection, Bates found that there was a major
advantage in mimicking the Heliconiids. Fragile,
slow-moving and brightly coloured, the Heliconiids
are ideal targets for insectivorous birds. Yet, birds
never touch them because they taste so bad.
Imagine that you\'re a delicious morsel of butterfly.
Wouldn\'t it be smart to mimic the appearance of
an unpalatable Heliconiid so that no bird would
bother you either? That\'s what Bates concluded
was happening in the Brazilian jungle among the
Pieridae. Today, the imitation of an inedible
species by an edible one is called Batesian
mimicry. Since Bates\' time, scientists have
unmasked hundreds of cases of mimicry in nature.
It hasn\'t always been an easy job, either, as when
an animal mimics not one, but several other
species. In one species of butterfly common in
India and Sri Lanka, the female appears in no less
than three versions. One type resembles the male
while the others resemble two entirely different
species of inedible butterflies. Butterflies don\'t
"choose" to mimic other butterflies in the same
way that you might pick out a costume for a
masquerade ball. True, some animals, such as the
chameleon, do possess the ability to change body
colour and blend in the with their surroundings.
But most mimicry arises through evolutionary
change. A mutant appears with characteristics
similar to that of a better protected animal. This
extra protection offers the mutant the opportunity
to reproduce unharmed, and eventually flourish
alongside the original. In the world of mimics, the
ant is another frequently copied animal, though not
so much by other ants as by other insects and
even spiders. Stoop down to inspect an ant
colony, and chances are you\'ll find a few
interlopers that aren\'t really ants at all but copycat
spiders (or wasps or flies). One way you might
distinguish between host and guest is by counting
legs: Ants have six legs while spiders have eight.
Look carefully and you might see a few spiders
running around on six legs while holding their other
two out front like ant feelers. COPYCATS
Mimicry can not only be a matter of looking alike,
it can also involve acting the same. In the
Philippine jungle there is a nasty little bug, the
bombardier beetle. When threatened by a
predator, it sticks its back end in the air, like a
souped-up sports car, and lets out a blast of
poisonous fluid. In the same jungle lives a cricket
that is a living xerox of the bombardier beetle.
When approached by a predator, the cricket will
also prop up its behind -- a tactic sufficient to
scare off the enemy, even though no toxic liquid
squirts out. Going one step further than that is a
native of the United States, the longicorn beetle,
which resembles the unappetizing soft-shelled
beetle. Not content to merely look alike, the
longicorn beetle will sometimes attack a
soft-shelled beetle and devour part of its insides.
By ingesting the soft-shelled beetle\'s bad-tasting
body fluid, the longicorn beetle gives itself a
terrible taste, too! Protection is by no means the
only advantage that mimicry offers. Foster care
can be another reward, as