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.)

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Name That Bug #1 – Revealed!

Chokecherry (Prunus virginiana)
Chokecherry (Prunus virginiana), Gregory Canyon, Boulder, Colorado. May 20, 2012.

Okay, I admit that was a little unfair. I’m not sure it would be possible to identify the host plant from that photo. So here’s a better picture of the plant.

a) What are these?

At first glance, one might look at these and wonder if they’re eggs. But they’re not separate from the leaf, but an outgrowth of it (difficult as that may be to tell from the original photo).

These are plant galls. A gall is just an abnormal growth of plant tissues, which can be caused by fungi, bacteria, insects, mites, and even parasitic plants.

b) Which plant are they on?

This is a chokecherry (Prunus virginiana), a widespread shrub in North America. It produces abundant very astringent berries which are an important food for animals (and with lots of sugar, make very tasty jelly for humans).

We’re two-thirds of the way there now. Many gall-producing arthropods are very host-plant specific, and we now know that these are a) galls and b) very likely specific to chokecherries and perhaps related plants.

c) Who made them?

A search for “chokecherry gall” brings up the Chokecherry Gall Midge (Contarinia virginianae ). Sounds promising, but it looks like this tiny fly’s larve induce galls on the fruit. But these galls are on the leaves, and look very different. So adding “leaf” to the search term, we get…

The Chokecherry Finger Gall Mite (Eriophyes emarginatae), which creates finger-shaped galls on the leaves of various plums and cherries, including chokecherries! Looks right to me:

Image of mysterious little white things on leaves
Chokecherry Finger Gall Mites (Eriophyes emarginatae) on Chokecherry (Prunus virginiana) leaves, Gregory Canyon, Boulder, Colorado, USA. May 20, 2012.
A mite is a tiny arachnid related to ticks. Gall mites of the family Eriophyidae are microscopic plant parasites. Some are major crop pests, while others can be used as biocontrol for weeds and invasive plant species.

So, what’s the take-home message here?

If you’re interested in identifying insects and other arthropods, a working knowledge of botany can be invaluable. Many groups–from gall mites to butterfly and moth caterpillars–are adapted to use only specific plants, and if you can identify the plant they’re living on or eating, it can vastly narrow your options. There are about 3,600 known species of gall mites–and there may be 10 times that number in reality–but identifying the plant as a chokecherry helped me to an identification pretty quickly.

And if you’re planning to collect and raise caterpillars at home, knowing how to identify their appropriate food plants is the difference between successful rearing and a dead caterpillar.

In the future, I’ll be writing a few more posts about different aspects of arthropod (mostly insect) identification from the point of view of a non-specialist who’s relatively new to this. It’s great to be able to use field guides–when they exist–or complicated taxonomic keys, but those can be pretty overwhelming initially, and I hope my less technical methods will be helpful to someone. My methods won’t work with all groups–species in some groups of insects can only be identified by close examination in hand, dissection of genitals, or other fiddly techniques that are out of reach to many people. But they have provided enough to keep me pretty busy, and they’re a start.

Name That Bug #1

Image of mysterious little white things on leaves
What are these? Gregory Canyon, Boulder, Colorado, USA. May 20, 2012.

I’m about to head up to Wyoming to camp for the weekend, but before I go, here’s a little entomological mystery for the approximately two people who might be reading this. I took this photo this spring up the in foothills around Boulder.

a) What are these?
b) Which plant are they on?
c) Who made them?

Hint: if you get what and which, you’re two-thirds of the way to who (which is how I was able to identify them). I’m using “bug” in the broad, non-scientific sense here, so they may or may not be created by insects. You can click on the photo for a larger image.

I’ll be back Sunday with the answers!

See Like A Bee: Ultraviolet Flower Photography

European Honeybee (Apis mellifera)
A European Honeybee (Apis mellifera) at Sawhill Ponds in Boulder, Colorado, USA. April 22, 2012.

PLEASE NOTE that I am NOT the photographer, and you should contact him directly through his website (linked below) if you are interested in using these images. According to his website, most uses will require a negotiable fee.

Some flowers and pollens fluoresce in interesting and sometimes surprising patterns under ultraviolet light. Alas, while pollinating insects can see these patterns perfectly to find the nectar and pollen, the human eye cannot without some help. Fortunately, professional photographer Bjørn Rørslett has photographed many of these flowers, revealing their UV and infrared patterns so we can “see” the flowers as bees do (more or less–the colors in UV photography are arbitrary).

Some of my favorites:

+Potentilla anserina L.
+Coreopsis sp.
+Crepis biennis
+Rudbeckia hirta
+Taraxacum vulgare
+Jasione montana
+Oenothera biennis
+Ranunculus ficaria
+Potentilla erecta
+Angelica sylvestris

Want to photograph your own UV flowers with a digital SLR camera? It’s complicated and not for the faint of heart or light of wallet, but Rørslett has kindly provided a tutorial if you decide to give it a try.

A version of this post was originally published on May 4, 2006. Somewhat bafflingly, this was by far the most popular post on my old blog, so I’m republishing it. Again, I am not the photographer of the linked images of flowers and I cannot provide permission to use them.