Sunday, August 10, 2014

Milkweed Bugs?

Large Milkweed Bug (Oncopeltus fasciatus) on a milkweed seed pod.

     I have always been fascinated by milkweed communities and all the adaptations that allow their inhabitants to survive there. Planting milkweeds for monarchs is getting more popular today, but many other creatures also benefit from milkweed (and many other plants can also be as good or better at providing backyard habitat as milkweeds). I am fairly familiar with these food webs, including the interesting bugs that inhabit them. But one of the things I love about my being a naturalist is that you learn new things just about every day. That was the case with these fairly well-studied insects which I will describe to you.
     First of all, milkweed bugs are brightly colored insects with sucking mouth parts that have evolved to (mostly) live on milkweeds. The toxins that normally protect the milkweeds (cardiac glycosides) are absorbed and used to then protect the milkweed bugs that feed on them. They advertise their toxicity with bright colors, like many milkweed feeding specialists do.
     Large Milkweed Bugs (Oncopeltus fasciatus) are one of the most studied insects in science. They prefer to feed on milkweed seeds, but can be reared on other types of seeds. They are thus easy to keep and are used in many science experiments. Those that do not feed on milkweed retain the warning coloration, but are not toxic. Adults are one of the few migratory insects we have, normally heading South during the Fall. They are distinguished from the other milkweed bugs by their larger size and the dark band across their backs.

Small Milkweed Bug (Lygaeus kalmii)

     Small Milkweed Bugs (Lygaeus kalmii) have a similar life cycle, but are more apt to feed on things other than milkweeds and do not migrate. They also will nectar on flowers, as you can see by the one in the picture feeding on Queen Anne's Lace. They are distinguished from other milkweed bugs, as most identification books tell you, by the "X" across there backs. However, it is also, I now know, good to look for the heart-shaped mark above the "X." 

False Milkweed Bug (Lygaeus turcicus)

     What most books do not tell you is that there are other species of milkweed bugs and that even many experts sometimes misidentify another milkweed bug for the Small Milkweed Bug. I discovered this for myself not too long ago when I spotted some milkweed bugs, but noticed that something wasn't quite right. First of all, most were not on milkweeds. That in and by itself is not as big a deal since milkweed bugs sometimes feed on other plants, as I have mentioned. But they also didn't look quite right and were also concentrated on False Sunflowers rather than the milkweeds that were right next to them. I snapped a couple of photos and that was that.

False Milkweed Bugs mating.

     However when I looked at my photos again, I realized that none of them were on milkweed and that they were mating, but not interested in the milkweeds. I then also saw that though I had Large Milkweed Bugs, that I appeared to have two other milkweed bugs that had slightly different patterns on their backs, including many that did not have the heart-shaped mark above the "X" that should have been there.
     A bit of research later, plus sending my photos to the experts at Bug Guide for confirmation, had me finding out that there was indeed another local milkweed bug that I had never heard about until I looked for it. I had now learned about False Milkweed Bugs, a species that is mistaken for Small Milkweed Bugs sometimes even by experts and in books/online photos. Although they can feed on milkweeds, they also feed on a variety of other plants as well. The mark they have above the "X" is slightly different from the heart-shaped one in the actual Small Milkweed Bug. 
     Most of my professional life I had been looking at not two, but three different species with somewhat different life cycles and niches in the natural world, despite my thinking I was fairly well versed in milkweed communities, or at least these fairly well-known creatures. That again is one of the things I love about my profession, the new discoveries, especially when they are triggered by my curiosity or when I notice something different. I love these little mysteries and when I learn something new, as I try to sort out what I consider to be nature's interconnected and fascinating puzzle. 


  1. how about those hundreds of golden colored aphids that love the swamp milkweed in my garden?

  2. Those are likely Oleander Aphids (Aphis nerii) and are not native. They originally are from the Mediterranean but came over on plants. They were able to feed on milkweeds and can be serious pests, sucking the stems and affecting the plant and any flower/seed production. Since they're not native, few predators eat them, though some ladybugs try. Squishing them and washing them off can help.