Aug

31

 "Evolving a Defense, Mimics Save Themselves":

The Canadian tiger swallowtail caterpillar is a plump green creature that spends all its time munching leaves. It ought to be an easy meal for a bird, yet many birds pass it by.

The caterpillar is protected by a remarkable defense, researchers have found: it tricks birds into thinking it's a snake.

The caterpillar grows concentric yellow and black rings that look like a giant pair of eyes. When the caterpillar senses a bird nearby, it quickly inflates the front part of its body, making it resemble a snake's head.

Astonishing as this deception may be, the tiger swallowtail is hardly unique. Many species have evolved ways to fool would-be predators. Some insects look like twigs, even mimicking the way that twigs sway in the breeze.

Harmless snakes scare off predators by mimicking the look of venomous ones. Some species of hoverflies have the yellow and black stripes of stinging wasps. They even pretend to sting their enemies despite having no stinger at all.

But mimicry has revealed a puzzle at its heart: Time and again, scientists find examples of overkill. Animals don't seem to receive an extra benefit from making their disguises more elaborate.


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  1. Andrew Goodwin on September 4, 2015 2:02 am

    The examples of mimicry given all involve replicating a venomous species. At least two factors are at work though far more are involved in some complete list:

    1) The predator will develop newly directed attacks away from the venom delivery mechanism if the venom gets too effective. That yields the mimicry impotent and makes the mimic easy prey.

    2) The predator develops immunity to the venom and attacks the mimicking creature if the venom gets too specific from the target prey.

    The fear is that the venomous species that do not target humans grow more venomous to humans by the day. The defense attacks of the venom givers, instead of their feeding attacks, are the concern. In some cases the new venom can grow to multiples of its potency in just generations.

    The disadvantaged creatures in this battle are those with slower reproductive cycles versus the target prey species. These venom effects compound like money with interest.

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