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The Great Imposters

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    Word Count: 1261Finding good daycare 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 layher eggs, she simply locates the nest of a nearbyEstrildid finch and surreptitiously drops the eggsinside. That’s the last the widow bird ever sees ofher offspring. But not to worry, because theEstrildid finch will take devoted care of theabandoned birds as if they were her own. Andwho’s to tell the difference? Though adult widowbirds and Estrildid finches don’t look at all alike,their eggs do. Not only that, baby widow birds aredead ringers for Estrildid finch chicks, both havingthe same colouration and markings. They even actand sound the same, thus ensuring that the widowbird nestlings can grow up among their aliennestmates with no risk of being rejected by theirfoster parents. MASTERS OF DISGUISE Thingsaren’t always as they seem, and nowhere is thismore true than in nature, where dozens of animals(and plants) spend their time masquerading asothers. So clever are their disguises that you’veprobably never known you were being fooled byspiders impersonating ants, squirrels that look likeshrews, worms copying sea anemones, androaches imitating ladybugs. There are even animalsthat look like themselves, which can also be aform of impersonation. The phenomenon ofmimicry, as it’s called by biologists, was first notedin the mid-1800s by an English naturalist, HenryW. Bates. Watching butterflies in the forests ofBrazil, Bates discovered that many members ofthe Peridae butterfly family did not look anythinglike their closest relatives. Instead they bore astriking resemblance to members of theHeliconiidae butterfly family. Upon closerinspection, Bates found that there was a majoradvantage in mimicking the Heliconiids. Fragile,slow-moving and brightly coloured, the Heliconiidsare ideal targets for insectivorous birds. Yet, birdsnever 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 ofan unpalatable Heliconiid so that no bird wouldbother you either? That’s what Bates concludedwas happening in the Brazilian jungle among thePieridae. Today, the imitation of an inediblespecies by an edible one is called Batesianmimicry. Since Bates’ time, scientists haveunmasked hundreds of cases of mimicry in nature.

    It hasn’t always been an easy job, either, as whenan animal mimics not one, but several otherspecies. In one species of butterfly common inIndia and Sri Lanka, the female appears in no lessthan three versions. One type resembles the malewhile the others resemble two entirely differentspecies of inedible butterflies. Butterflies don’t”choose” to mimic other butterflies in the sameway that you might pick out a costume for amasquerade ball. True, some animals, such as thechameleon, do possess the ability to change bodycolour and blend in the with their surroundings.

    But most mimicry arises through evolutionarychange. A mutant appears with characteristicssimilar to that of a better protected animal. Thisextra protection offers the mutant the opportunityto reproduce unharmed, and eventually flourishalongside the original. In the world of mimics, theant is another frequently copied animal, though notso much by other ants as by other insects andeven spiders. Stoop down to inspect an antcolony, and chances are you’ll find a fewinterlopers that aren’t really ants at all but copycatspiders (or wasps or flies). One way you mightdistinguish between host and guest is by countinglegs: Ants have six legs while spiders have eight.

    Look carefully and you might see a few spidersrunning around on six legs while holding their othertwo out front like ant feelers. COPYCATSMimicry can not only be a matter of looking alike,it can also involve acting the same. In thePhilippine jungle there is a nasty little bug, thebombardier beetle. When threatened by apredator, it sticks its back end in the air, like asouped-up sports car, and lets out a blast ofpoisonous fluid. In the same jungle lives a cricketthat is a living xerox of the bombardier beetle.

    When approached by a predator, the cricket willalso prop up its behind — a tactic sufficient toscare off the enemy, even though no toxic liquidsquirts out. Going one step further than that is anative of the United States, the longicorn beetle,which resembles the unappetizing soft-shelledbeetle. Not content to merely look alike, thelongicorn beetle will sometimes attack asoft-shelled beetle and devour part of its insides.

    By ingesting the soft-shelled beetle’s bad-tastingbody fluid, the longicorn beetle gives itself aterrible taste, too! Protection is by no means theonly advantage that mimicry offers. Foster carecan be another reward, as proven by the Africanwidow bird. And then there’s the oldwolf-in-sheep’s-clothing trick, which biologists callaggressive mimicry. The master practitioner ofaggressive mimicry is the ocean-going anglerfish.

    Looking like a stone overgrown with algae, theanglerfish disguises itself among the rocks andslime on the ocean bottom. Protruding from itsmouth is a small appendage, or lure, with all thefeatures of a fat, juicy pink worm. The anglerfishlacks powerful teeth so it can’t take a tight grip onits prey. Instead, it waits motionless until a smallfish shows interest in the lure, and then wiggles thelure in front of the fish’s mouth. When the small fishis just about to snap at the lure, the anglerswallows violently, sucking the fish down its hatch.

    Diner instantly becomes dinner. SEXUALIMITATORS Of all the many impostures found innature, probably the sneakiest are those of thesexual mimics: males who imitate females to gainan advantage at mating time. Here in Ontario wehave a sexual mimic, the bluegill fish. Male bluegillscome in two types: the standard male and thesatellite male, which looks just like a femalebluegill. In preparation for mating, the standardmale bluegill performs the job of building the nest,where he bides his time until a female enters it tospawn. Satellite fish don’t build nests, choosinginstead to hover around the nest of a standardmale until the moment when a pregnant femaleenters. The satellite fish follows her into the nest,deceiving the nestbuilder into believing that he isnow in the presence of two females. The three fishswim around together, and when the female dropsher eggs, both males release a cloud of sperm.

    Some of the eggs are fertilized by the residentmale, some by the satellite male, thus passing onpassing on different sets of male genes to a newgeneration of bluegills. Another case of sexualmimicry has recently been uncovered in Manitobaamong the red-sided garter snakes. The little townof Inwood, Manitoba and the surroundingcountryside is garter snake heaven, where you canfind the largest snake colonies on Earth. Everyspring, the red-sided garter snake engages in acurious mating ritual. Soon after spring thaw, themales emerge first from their winter cave andhover nearby. The females then slither out a few ata time, each one exuding a special “perfume”which signals to the fellows that she’s ready tomate. At first whiff of this lovely odour, a mass offrenetic males immediately besieges the female,wrapping her up in a “mating ball” of 10, 20 orsometimes as many as 100 writhing males, allhoping to get lucky. Scientists have nowdiscovered that some male red-sided garters giveoff the same perfume as the female, and they dothis while intertwined in the mating ball. Male andfemale red-sided garters look exactly alike, so themale with the female scent can effectively distractmany of the males from the real female, giving theimposter a better shot at getting close to thefemale and impregnating her. Males passing asfemales, fish as bait, beetles as ants — amidst allthis confusion, it still sometimes pays to just beyourself, which could certainly be the motto of theamazing hair-streak butterfly family. Decoratingthe hair-streak’s lower hind wings are spots thatlook like eyes, and out-growths that look likeantennae, creating the illusion that the butterfly hasa second head. Whenever the hair-streak alights, itjerks its dummy antennae up and down whilekeeping its real antennae immobile. Presumably,this dummy head exists to distract predators. If so,we finally have the first scientific proof that twoheads are better than one.

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