As the days get shorter the migrating wildlife is starting to think about moving southward.  Not in flocks yet but individually you can see creatures drifting in that direction, grabbing a bite where they can along the way.

We see monarch butterflies passing through the local parks this time of year.  They usually check out the milkweed that's in bloom and the other summer flowers in the prairies.  At a glance the bit of orange drifting by on the wind usually triggers "monarch" in my brain but the other day I saw one that seemed not quite right.

Mimicry is a great natural defense, as this butterfly shows.  This is a viceroy butterfly, not a monarch.  What attracted my attention was the size - it didn't seem large enough and by this time of the year monarchs have reached their adult size.  I wasn't sure until I got to my computer for a comparison.  Here's a monarch.

A monarch doesn't have a line along the lower wing connecting the thinner black lines whereas a viceroy does.  Also, the average size of a viceroy is smaller than a monarch, just enough to be noticeable.

Monarchs feed on milkweed, which imparts a bitter taste to anything trying to feed on them.  It's why you don't see birds with monarch butterflies in their bill.  They've learned that orange and black color means "this doesn't taste good."  Viceroy butterflies evolved to mimic this warning, meaning birds and other predators leave them alone.  It is odd, though.  Birds have shown good eyesight and pattern recognition skills. You'd think they would have figured out this subtle difference in appearance between the two butterflies.  Guess better safe than sorry for the bird, and a benefit to the viceroy.