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 femalewidow bird to lay her eggs, she simply locates the nest of a nearbyEstrildid finch and surreptitiously drops the eggs inside. That’s the last the widow bird ever sees of her offspring. But not toworry, because the Estrildid finch will take devoted care of the abandonedbirds as if they were her own. And who’s to tell the difference? Though adult widow birds andEstrildid finches don’t look at all alike, their eggs do.
Not only that,baby widow birds are dead ringers for Estrildid finch chicks, both havingthe same colouration and markings. They even act and sound the same, thusensuring that the widow bird nestlings can grow up among their aliennestmates with no risk of being rejected by their foster parents. MASTERS OF DISGUISEThings aren’t always as they seem, and nowhere is this more true thanin nature, where dozens of animals (and plants) spend their timemasquerading as others. So clever are their disguises that you’ve probablynever known you were being fooled by spiders impersonating ants, squirrelsthat look like shrews, worms copying sea anemones, and roaches imitatingladybugs. There are even animals that look like themselves, which can alsobe a form of impersonation.
The phenomenon of mimicry, as it’s called by biologists, was firstnoted in the mid-1800s by an English naturalist, Henry W. Bates. Watchingbutterflies in the forests of Brazil, Bates discovered that many members ofthe Peridae butterfly family did not look anything like their closestrelatives. Instead they bore a striking resemblance to members of theHeliconiidae butterfly family. Upon closer inspection, Bates found that there was a major advantagein mimicking the Heliconiids.
Fragile, slow-moving and brightly coloured,the Heliconiids are 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 besmart to mimic the appearance of an unpalatable Heliconiid so that no birdwould bother you either? That’s what Bates concluded was happening in theBrazilian jungle among the Pieridae.
Today, the imitation of an inediblespecies by an edible one is called Batesian mimicry. Since Bates’ time, scientists have unmasked hundreds of cases ofmimicry in nature. It hasn’t always been an easy job, either, as when ananimal mimics not one, but several other species. In one species ofbutterfly common in India and Sri Lanka, the female appears in no less thanthree versions. One type resembles the male while the others resemble twoentirely different species of inedible butterflies.
Butterflies don’t “choose” to mimic other butterflies in the same waythat you might pick out a costume for a masquerade ball. True, someanimals, such as the chameleon, do possess the ability to change bodycolour and blend in the with their surroundings. But most mimicry arisesthrough evolutionary change. A mutant appears with characteristics similarto that of a better protected animal.
This extra protection offers themutant the opportunity to reproduce unharmed, and eventually flourishalongside 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 fewinterlopers that aren’t really ants at all but copycat spiders (or wasps orflies). One way you might distinguish between host and guest is by countinglegs: Ants have six legs while spiders have eight. Look carefully and youmight see a few spiders running around on six legs while holding theirother two out front like ant feelers.
COPYCATS Mimicry can not only be a matter of looking alike, it can also involveacting the same. In the Philippine jungle there is a nasty little bug, thebombardier beetle. When threatened by a predator, it sticks its back end inthe air, like a souped-up sports car, and lets out a blast of poisonousfluid. In the same jungle lives a cricket that is a living xerox of thebombardier beetle. When approached by a predator, the cricket will alsoprop up its behind — a tactic sufficient to scare off the enemy, eventhough no toxic liquid squirts out. Going one step further than that is a native of the United States, thelongicorn beetle, which resembles the unappetizing soft-shelled beetle.
Not content to merely look alike, the longicorn beetle will sometimesattack a soft-shelled beetle and devour part of its insides. By ingestingthe soft-shelled beetle’s bad-tasting body fluid, the longicorn beetlegives 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. Andthen there’s the old wolf-in-sheep’s-clothing trick, which biologists callaggressive mimicry. The master practitioner of aggressive mimicry is the ocean-goinganglerfish.
Looking like a stone overgrown with algae, the anglerfishdisguises itself among the rocks and slime on the ocean bottom. Protrudingfrom its mouth is a small appendage, or lure, with all the features of afat, juicy pink worm. The anglerfish lacks powerful teeth so it can’t take a tight grip onits prey. Instead, it waits motionless until a small fish shows interest inthe lure, and then wiggles the lure in front of the fish’s mouth. When thesmall fish is just about to snap at the lure, the angler swallowsviolently, sucking the fish down its hatch. Diner instantly becomes dinner.
SEXUAL IMITATORSOf all the many impostures found in nature, probably the sneakiest arethose of the sexual mimics: males who imitate females to gain an advantageat 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 thejob of building the nest, where he bides his time until a female enters itto spawn. Satellite fish don’t build nests, choosing instead to hoveraround the nest of a standard male until the moment when a pregnant femaleenters. The satellite fish follows her into the nest, deceiving thenestbuilder 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 theresident male, some by the satellite male, thus passing on passing ondifferent sets of male genes to a new generation of bluegills. Another case of sexual mimicry has recently been uncovered in Manitobaamong the red-sided garter snakes. The little town of Inwood, Manitoba andthe surrounding countryside is garter snake heaven, where you can find thelargest snake colonies on Earth. Every spring, the red-sided garter snake engages in a curious matingritual. Soon after spring thaw, the males emerge first from their wintercave and hover nearby.
The females then slither out a few at a time, eachone exuding a special “perfume” which signals to the fellows that she’sready to mate. At first whiff of this lovely odour, a mass of freneticmales 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 getlucky. Scientists have now discovered that some male red-sided garters giveoff the same perfume as the female, and they do this while intertwined inthe mating ball. Male and female red-sided garters look exactly alike, sothe male with the female scent can effectively distract many of the malesfrom the real female, giving the imposter a better shot at getting close tothe female and impregnating her. Males passing as females, fish as bait, beetles as ants — amidst allthis confusion, it still sometimes pays to just be yourself, which couldcertainly be the motto of the amazing hair-streak butterfly family. Decorating the hair-streak’s lower hind wings are spots that look likeeyes, and out-growths that look like antennae, creating the illusion thatthe butterfly has a second head.
Whenever the hair-streak alights, itjerks its dummy antennae up and down while keeping its real antennaeimmobile. Presumably, this dummy head exists to distract predators. If so,we finally have the first scientific proof that two heads are better thanone.