Milkweed Bug infestation of Butterfly Weed

by | May 3, 2011 | 10 comments

Pictured here is the original idea — purple Liatris spicata spikes paired against orange Butterfly Weed (Asclepias tuberosa) blossoms in one of our backyard flower beds. Both attract butterflies, both are easy-to-grow perennials, and both have similar tight flower clusters — but there’s a nice contrast of forms and colors. Last spring, we decided to expand on this, by devoting one flower bed entirely to this combination. At that time, we had never heard of the Milkweed Bug.

Now, we did know that Liatris tends to get chewed on. It is not unusual to find a new spike felled every few days by vandal rabbits. Our hope was for strength in numbers. If we planted a whole bunch of Liatris, then a downed spear here and there would not be missed.

Amy bought a plastic box of 25 Liatris corms for $5 at Menards and carefully planted them root-side down in the flower bed where we had already established a good many small Butterfly Weed plants .

Why Butterfly Weed?

Butterfly Weed (Asclepias tuberosa) is so named not only because butterflies feed on its nectar, but because it is a host plant for the Monarch Butterfly (Danaus plexippus) — as are other Asclepias species, such as the less beautiful Common Milkweed (Asclepias syriaca). Monarch moms lay their eggs on these plants, which are then eaten by the resulting caterpillars.

While Butterfly Weed provides nutrition for the Monarch caterpillars, it also arms them with a toxin which makes Monarch Butterflies distasteful to predators. I was hoping this might also offer some protection to the interspersed Liatris.

Instead, within two days of Amy’s careful planting, marauding Gray Squirrels dug up 24 of the 25 Liatris corms, chewing on each one before discarding it to dig up the next.

Only the Butterfly Weed (and one lonely Liatris) remained. In time, Monarch Butterflies did indeed find our patch. They danced happily from plant to plant laying eggs all over. Before long, we were spotting numerous caterpillars and were very pleased to play some small part in the survival of this majestic threatened species.

Milkweed Bug infestation

Then the first of the peculiar bugs appeared — orange and black guys which flew a little, but mostly just hung out on our Butterfly Weed plants. Some of the bugs would pair off, rear end to rear end. As we read online, this is how Milkweed Bugs (Oncopeltus fasciatus) mate. Soon, there were lots and lots of Milkweed Bugs all over our Butterfly Weed.

Besides mating, Milkweed Bugs eat milkweed seeds. They have a long mouthpart known as a “rostrum” which they use to pierce the plant’s seed pods and suck juices right out of the seeds themselves. As with Monarch Butterflies, the toxic glycosides from the plant make the bug distasteful to predators, and their orange color serves as a warning. Birds know not to eat them.

As far as I could find out, there wasn’t much we could do to control these bugs. Poison would also harm the very butterflies and birds we want to encourage. One article I read suggested squishing the bugs individually, but I just don’t have that kind of free time.

Within a couple of weeks, our once beautiful Butterfly Weed looked discolored and desperate. Its withered seed pods opened prematurely to release their downy contents before all hope was lost. Not fluffy enough to fly, the fuzz mostly clung to the ratty plants while pulsing swarms of Milkweed Bugs backed into each other in ecstatic frenzy.

This year, all of those Butterfly Weed plants have been cleared out. We’ll keep the one or two plants we have elsewhere. Liatris, however, will get another try. This time around, Amy has planted 50 corms — and staked a wire mesh over them to thwart the squirrels until they start sprouting.

Milkweed Bug control

I say this below in the comments, but I thought I would add it here as well: We have had no further infestations of Milkweed Bugs since we started plucking the seed pods from the Butterfly Weed as soon as they appear. This has no adverse effect on the plant. In fact, it seems to promote a weak second flowering. We have no use for the seeds, and this also prevents their silky floss from blowing all over the yard.

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