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 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. SEXUAL IMITATORS
 
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 lucky.
 
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.