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

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