Friday, March 1, 2013

Mom! The Viceroy won't stop copying me!

When used as a verb the word mimic means to copy or imitate something closely.  When a species is described as a mimic, that means it copies something about another species.  The mimicking species may be copying the looks, behavior, sounds, or even the smell of the mimicked species.  The mimic will only do this if copying the other organism will help it survive - usually mimicry is used to avoid predators.

There are several different forms of mimicry in nature.  The two most well known forms are Batesian and Mullerian mimicry.  Both forms of mimicry are named after the people that first recognized and publicized the action.  Batesian mimicry is named after British scientist and explorer Henry Walter Bates (1825 - 1892).  Mullerian mimicry is named after German Fritz Müller (1821 - 1897).

Batesian mimicry is a form of mimicry in which a harmless species copies the warning signs of a harmful species to scare away predators.  This type of mimicry is very common in insects.  Many species of harmless insects have evolved to have the yellow and black color pattern of bees and wasps.  Appearing to have the ability to sting will scare away many potential predators.  Harmless insects that use this strategy include flies, beetles, and moths.

One good example of Batesian mimicry is found in the harmless Snowberry Clearwing moth ( Hemaris diffinis).  Also known as a Hummingbird Moth or Bumblebee Moth, the Snowberry Clearwing has a striped yellow and black abdomen that mimics a large bee such a Bumble Bee or Carpenter Bee.

Snowberry Clearwing on Pickerelweed

Snowberry Clearwing on Pickerelweed

Eastern Carpenter Bee on Swamp Milkweed

Mullerian mimicry is a type of mimicry in which two distasteful, poisonous, or otherwise harmful species have evolved to resemble each other - sharing the warning signs that keep predators away.  One example of Mullerian mimicry is between Viceroy (Limenitis archippus) and Monarch (Danaus plexippus) butterflies.  It was thought for many years that this was a case of Batesian mimicry, with a harmless Viceroy mimicking a distasteful Monarch, but studies done in the 1990s showed that Monarchs and Viceroys both taste bad to predators such as birds - making it a case of Mullerian mimicry.  The Monarch tastes bad because its caterpillars feed on milkweed plants which produce a toxic sap that is stored in the body of the Monarch.  Viceroys taste bad because their caterpillars feed on the leaves of willow trees which contains an acid that gives the Viceroy a bitter taste.  The taste of Monarch and Viceroys does vary depending on how much toxic substance the plant they were eating contains.

Both the Monarch and Viceroy are large orange and black butterflies with white spots around the margins of their wings.  The Viceroy can be identified by a curved line that crosses its hind wings - looking like a half-circle or smile.  The Monarch lacks this line.  The two can be very difficult to distinguish in flight.  This makes both of them less susceptible to predation and increases their chances of survival.

Viceroy Butterfly - note curved line crossing hind wings
Monarch Butterfly on Common Milkweed - note the lack a line crossing its hind wings

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