Monarch Butterfly

I found this beautiful fellow while on a walk recently.  I thought it was a Monarch, but had to look him up to be sure.  He was indeed a Monarch, but I learned that he has a look-alike, which is the Viceroy butterfly.

Monarch butterfly on swamp milkweed

Monarch butterflies are bigger than Viceroys, but I didn't have the two different kinds sitting side by side in order to do a comparison.  To determine this fellow's identification, I had to look for other differences.

One difference is that the bottom row of orange spots on a Monarch are concave, meaning they stick out.  On a Viceroy they are convex, or indented.  That way my main clue.  Also, the Viceroy has a black line that runs through his bottom wings, and the Monarch does not.  Additionally, male Monarchs have two black scent glands on their bottom wings, as pictured below.  Viceroys don't have those spots.

Female Monarchs don't have the black scent glands, but they do have thicker black veining between their orange spots.  Due to this factor, I would guess that the butterfly in the first photo above is a female.

Monarch butterfly on pea partridge

The Monarch is one of the biggest butterflies around, and is well-known for its coloring, and amazing migration journeys.  A chemical in the milkweed they love to feeds on causes them to taste bitter when chomped on by predators.  Predators soon learn to leave Monarchs alone, and anything that even looks like them, such as the Viceroys.  Great defense mechanisms!