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Thursday, September 5, 2013

How to Identify a Monarch Butterfly

It's Monarch season in Vermont!  I've spent the past several Wednesday afternoons walking with groups of eager kids and adults, nets in hand, through the fields at NBNC as part of our Monarch tagging programs.  Occasionally, I have heard an excited shout, "Look! A Monarch!"  As of yet, they've all been false alarms.  Our butterfly hunters have been tricked by the Viceroy.

click on the picture for a larger view

Monarchs are one of many orange-and-black butterflies that float across fields in Vermont.  The fritillaries are a group of orange butterflies that mostly have black spots (rather than stripes).  The crescents and skippers can be orange, but are significantly smaller than Monarchs at roughly 1/4 the size, or even smaller.  Several others can look similar, but it is the Viceroy that causes the greatest source of confusion.

The Viceroy is smaller than the Monarch.  This characteristic is most obvious when looking at a butterfly up close.  But be careful when using size as a reference!  The largest Viceroys can top out at 81 mm and the smallest Monarchs can be just 91 mm... a difference that is not easily discernible from a distance.

The most useful tool for distinguishing these species is a black line on the hind (bottom) wings.  This line, running roughly parallel to the wing margin, crosses through all the other vertical veins on the hind wing.  Whether viewed from above or below, this line is always visible.  When you learn this field mark, you will soon be able to identify Viceroys even from a distance.  

Now that you are en expert in Monarch identification, keep your eyes peeled for this magnificent butterfly!  The month of September is the peak of the Monarch's migration, and with their numbers down this year, keeping track of them is more important than ever.  Have you seen Monarchs or Viceroys lately?  Let us know!

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