Why milkweed is the best plant: wasps!

Potter or mason wasp (Subfamily Eumeninae)
A potter or mason wasp (Subfamily Eumeninae) feeding on milkweed nectar, Barr Lake State Park, Colorado, USA. July 1, 2012.

Not only is milkweed food for adorable monarch butterfly caterpillars, but the right patch of milkweed can attract a host of interesting pollinators. After we checked out the burrowing owls the other weekend, we stopped at Barr Lake State Park for brunch, and I had to check out this fine stand of pink milkweed in full flower.

I’m kicking myself now for not taking some pictures of the actual plant. For one thing, it might have helped with identification, as some milkweed-loving insects are adapted to specific species, plus it’s generally a good habit to get into. In my defense, I was really excited about the wasps.

Because really, look at this gorgeous green-eyed square-headed wasp (Tachytes sp.). Who wouldn’t get excited?

Square-headed wasp (Tachytes sp.)

There was a thread-waisted wasp (Prionyx sp.) gamely flying around feeding despite missing at least one and a half legs (it’s rough sometimes, being an insect):

Thread-waisted wasp (Family Sphecidae)

And a bunch of attractive yellow-spotted scoliid wasps, probably Scolia nobilitata:

Scoliid wasp (Scolia nobilitata)

But the mystery was this milkweed beetle (Tetraopes sp.):

Milkweed beetle (Tetraopes pilosus)

Most milkweed beetles are bright red and black–like many insects which feed on milkweed, including monarch caterpillars and milkweed bugs, they exhibit aposematic coloring. Milkweed contains toxins that make it unpalatable to many animals, and aposematic coloring indicates to predators that insects like milkweed beetles are also unpalatable.

There are a few species of milkweed beetle that sometimes exhibit pale forms, but the only one I know of that’s this pale is Tetraopes pilosus. T. pilosus does live in Colorado…so what’s the catch? Remember, earlier I mentioned that a lot of insects that eat milkweed are host-plant specific, and milkweed beetles may fall into this category. T. pilosus feeds on Asclepias arenaria and A. tuberosa, both white-flowered, less showy species, that are commonly found in sandhills.

While I can’t identify this milkweed for certain, I think it was probably A. speciosa, and definitely not either of the host plants for T. pilosus. It was growing at the edge of a grassy meadow near a lake, about as far from sandhill country as a habitat can be.

But the beetle really can’t be anything other than T. pilosus, and was identified as such by Michael C. Thomas over at BugGuide. So my best guess here is that milkweed beetles are not quite that host- or habitat-specific. If anyone has some insight on this, I’d love to hear it!

(Thanks to John S. Ascher, Michael C. Thomas, Ken Wolgemuth, and Eric R. Eaton at BugGuide for identification help. Remaining errors are mine.)