Milkweed plants have flowers that attract butterflies, bees, and other pollinators. In fact, it is the only host plant of the monarch butterfly. But there are a lot of insects attracted to milkweed. This article discusses some fascinating facts about milkweed you probably didn’t know, and the plant’s unique relationship to many insects.
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Image courtesy of Eric Heupel on Flickr
What is A Butterfly Host Plant?
A butterfly host plant provides nectar for adult butterflies and is their preferred site for laying eggs. Not only is milkweed the preferred food source for adult monarch butterflies, the caterpillars prefer it as well.
There are many types of milkweed, and I happen to have two of them in my yard: honeyvine milkweed (Cynanchum laeve) and butterfly milkweed (Asclepias tuberosa). Swamp milkweed (Asclepias incarnata) is another popular type for wet areas. There are many more varieties. I like this assortment of 6 types of butterfly weed seed packets.
Poison: Nature’s Protective Strategy
As the blooming season winds down, it seems like the action might be done for the year. But for milkweed, it is just getting started! In the late summer, you can spot monarch caterpillars, milkweed aphids, and large milkweed bugs all feeding on the milkweed plant–two of these are good, one not so good. All of them are here to dine on the milky plant juices that give the plant its name. These insects have evolved to take in the toxin glycoside that exists within the plant’s juices, which then makes them poisonous to anything that might want to eat them.
Honeyvine milkweed is an invasive vine, impossible to get rid of, and something I would never grow by choice. Unfortunately, our neighbor allows it to take over our shared fence, and it spreads by seed and roots. I am constantly pulling the vines that threaten to take over our entire tenth acre.
Milkweed aphids are reportedly non-native and invasive, and make it hard for the monarch caterpillars to get enough to eat since they cover the plant. Garden experts generally recommend a soap and water spray (when caterpillars aren’t present) to wash the aphids off the plant, since there are no known predators that can ingest the now-toxic insects that have been feeding on the milkweed.
Large Milkweed Bug
As I was doing my daily walk around the garden yesterday–inspecting everything for unusual signs and making harvest lists–I noticed the immature milkweed seed pods covered in red and black bugs. I’ve seen this in past years, but I just assumed that they were some aspect of the milkweed aphid’s life cycle. With a little more digging, I discovered that they are appropriately called the large milkweed bug (Oncopeltus fasciatus). As far as I can tell, they are common and not invasive. We will continue to observe.
As you can see, milkweed is an interesting plant that is both important for the monarch butterfly as well as a number of other insects. Sow milkweed seeds in the fall for blooms the following year.
Are you growing milkweed in your yard? Have you noticed any of these insects on your plants? Do you do anything special to encourage the monarchs?