The Great Imposters Essay

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.
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.
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 proven by the
African widow bird. And then there’s the old wolf-in-sheep’s-
clothing trick, which biologists call aggressive mimicry.
The master practitioner of aggressive mimicry is the ocean-
going anglerfish. Looking like a stone overgrown with algae, the
anglerfish disguises itself among the rocks and slime on the
ocean bottom. Protruding from its mouth is a small appendage, or
lure, with all the features of a fat, juicy pink worm.
The anglerfish lacks powerful teeth so it can’t take a tight
grip on its prey. Instead, it waits motionless until a small fish
shows interest in the lure, and then wiggles the lure in front of
the fish’s mouth. When the small fish is just about to snap at
the lure, the angler swallows violently, sucking the fish down
its hatch. Diner instantly becomes dinner.
Of all the many impostures found in nature, probably the
sneakiest are those of the sexual mimics: males who imitate
females to gain an advantage at mating time. Here in Ontario we
have a sexual mimic, the bluegill fish. Male bluegills come in
two types: the standard male and the satellite male, which looks
just like a female bluegill.
In preparation for mating, the standard male bluegill
performs the job of building the nest, where he bides his time
until a female enters it to spawn. Satellite fish don’t build
nests, choosing instead to hover around the nest of a standard
male until the moment when a pregnant female enters. The
satellite fish follows her into the nest, deceiving the
nestbuilder into believing that he is now in the presence of two
females. The three fish swim around together, and when the female
drops her eggs, both males release a cloud of sperm. Some of the
eggs are fertilized by the resident male, some by the satellite
male, thus passing on passing on different sets of male genes to
a new generation of bluegills.
Another case of sexual mimicry has recently been uncovered in
Manitoba among the red-sided garter snakes. The little town of
Inwood, Manitoba and the surrounding countryside is garter snake
heaven, where you can find the largest snake colonies on Earth.
Every spring, the red-sided garter snake engages in a curious
mating ritual. Soon after spring thaw, the males emerge first
from their winter cave and hover nearby. The females then slither
out a few at a time, each one exuding a special “perfume” which
signals to the fellows that she’s ready to mate. At first whiff
of this lovely odour, a mass of frenetic males immediately
besieges the female, wrapping her up in a “mating ball” of 10, 20
or sometimes as many as 100 writhing males, all hoping to get
Scientists have now discovered that some male red-sided
garters give off the same perfume as the female, and they do this
while intertwined in the mating ball. Male and female red-sided
garters look exactly alike, so the male with the female scent can
effectively distract many of the males from the real female,
giving the imposter a better shot at getting close to the female
and impregnating her.
Males passing as females, fish as bait, beetles as ants —
amidst all this confusion, it still sometimes pays to just be
yourself, which could certainly be the motto of the amazing hair-
streak butterfly family.
Decorating the hair-streak’s lower hind wings are spots that
look like eyes, and out-growths that look like antennae, creating
the illusion that the butterfly has a second head. Whenever the
hair-streak alights, it jerks its dummy antennae up and down
while keeping its real antennae immobile. Presumably, this dummy
head exists to distract predators. If so, we finally have the
first scientific proof that two heads are better than one.

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