Sunday, November 2, 2014

The three milkweed butterflies of the United States

Queens (Danaus gilippus) were... not uncommon.
I have had a wonderful time exploring central and south Texas over the past few weeks. After attending the Texas Butterfly Festival, I feel it is appropriate to write a brief butterfly-centric post. I see more of the ilk in my future-- I saw so many new butterflies, including tropical species! At any rate, it's been a blast.

The controversial non-native tropical milkweed
(Asclepias curassavica). The leaves are evergreen. 
One of the highlights of my travels has been to finally see a soldier butterfly (Danaus eresimus). Soldier butterflies, like monarchs and queens, use milkweed exclusively as their larval host plant. Unlike monarchs and queens, their range barely extends into the United States. The subtropical tips of of south Texas and Florida are the only places you can really hope to find them. I was fortunate enough to see all three milkweed butterflies in the same garden on the same day (!) in Mission, Texas at the National Butterfly Center. They were really loving the betony-leaf mistflower (Conoclinium betonicifolium)

This is the best time to see butterflies down in south Texas' Rio Grande Valley. This area hits its peak butterfly density in October and November. The Rio Grande Valley is special. It marks the northern-most extent of number of largely tropical butterflies- a few of which I saw and will cover in a future post.

The monarch butterfly
Because the queens, soldiers, and monarchs (Danaus plexippus) are all very similar in appearance, I thought it would be useful to include pictures of all three to compare the various field markings. First:  the classic monarch butterfly. Flashy and readily seen, though threatened by habitat loss in much of North America, this species can be found from Texas to Canada. They are the only milkweed butterfly with a confirmed long-distance migration, and they are much larger than both the queens and soldiers. Their size and bright orange coloration make them pretty easy to distinguish. Also, their veins are a high-contrast black instead of brown or undifferentiated in color from the wing.

Mating queens
Queen butterflies (Danaus gilippus) are smaller, more brown than orange, and they don't have the same contrasting black venation visible on their dorsal (topside) as  monarchs. They also have two lines of white dots on the dorsal side of their forewing (leading wing), versus the single line observed in soldiers. Their overall color is darker and duller. Queens are quite common in the parts of south Texas I visited- they are much more frequently found than monarchs along the coast here. They are something of a southwestern species.

Soldier butterflies are definitely the most uncommon of the three milkweed-feeders. Sometimes they stray into southern Arizona, but they primarily stick to the subtropical areas of the United States. They are the veritable four-leaf clover in the field. In addition to being distinguished from queens by their single (instead of double) line of white dots on the forewing, they also have a dusky dark patch in the middle of their hindwing. Overall, they are a rich shade of brown.

The uncommon, hard to spot soldier butterfly

So that's it! The three North American milkweed butterflies. Stay tuned for a more lengthy update on the other unusual species I found down on the border...

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