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. 