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.
monarch caterpillar
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.
Cool, right?
Milkweed Aphids
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.
honeyvine milkweed on my neighbor’s fence with milkweed aphids
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.
Large Milkweed Bugs on Milkweed Seed Pod
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.
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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?
Deb Neyens says
Interesting. We grow milkweed for the monarchs, and just this year we noticed for the first time the red and black bugs. I took a photo, but haven’t had time to research them yet. Have not had an issue with aphids.
Dave Reyman says
I have found that these are described as beetles. Question: are they edible?
Rebecca says
I was so excited to see the milkweed article. Recently out of the blue, milkweed started growing outside under my bedroom window. The flowers were a purple color, and the lovely scent drifted into my window. I have the small pods forming now. I knew that monarchs lay their eggs in the pods, so I’ve been doting over my milkweeds and they are multiplying in number. I hope to find monarchs eventually. They have steadily decreased in number which is alarming to me, and hope that by having my little haven for them, they will prosper here. Thank you for highlighting the milkweed and the monarchs.
Amy says
Plant it and they will come! (We hope) 🙂
I recently read an article that gave me hope: Monarch Butterfly Population More Than Triples Over Last Year.
Rebecca says
Wonderful! Thank you Amy 🙂
Anna says
We saw a lot of caterpillars in 2016 – not so many this year in spite of the new plantings we have – not sure why
Amy says
Nature ebbs and flows. I bet annual rainfall and temperatures will affect the numbers from one year to another. Of course, there are more dire reasons why numbers may have dropped, but let’s hope it was just a seasonal ebb 🙂
Don says
Sometimes it’s a nearby wasp nest that is taking the larva
Michelle says
sorry but i need to tell you that LADYBUGS are in fact predators who can and do eat the aphids and you can buy them online as well as local garden centers, usually bout 1500 of them in a bag if i remember correctly….. the larva of the ladybugs look kinda scary little things , we call them alligator ladybugs because theyre little flattish black spiky looking bugs before they become the beautiful red and other colored beetles we all know and love….. i use NO chemicals on my yard or flowers ever, and have found mother nature takes care of a lot of our problems, ive seen my milkweeds covered in yellow aphids and only two ladybugs and the next few days theyve eaten all the aphids, and i have a LOT of big milkweeds growing each year that ive planted for the monarchs
http://articles.latimes.com/2012/nov/09/news/la-lh-milkweed-aphids-monarch-butterfly-eggs-20121104
Michelle says
forgot to mention also that ive seen monarchs lay eggs on and they seem to actually prefer honeyvine milkweed to regular milkweed , even though it is very invasive, it is still a milkweed plant , its still a great hostplant imo and nectar source for butterflies in general… my neighbors have planted no milkweeds although ive offered seeds etc but they do have honeyvine milkweed vines that have made themselves at home on their hedges, fences etc and weve found monarch caterpillars of all sizes and instars on their vines munching away happily and i see monarchs laying eggs on their vines from across the street when my flowerbeds are full of regular milkweeds . i think if people would educate themselves and each other , theyd find that most plants and trees are actually host plants for butterflies and would let more grow
Lisa Aucoin says
I was pleasantly surprised to find monarch caterpillars on our new swamp milkweed plant in September. Five caterpillars but could find only one chrysalis later on. My butterfly weed had two caterpillars, found at maybe the first and second instar stage but couldn’t find them the next day.
Lots of milkweed bugs and milkweed aphids on my swamp milkweed plant. However, the milkweed did not bloom. I read that it might have been because the plant was still young? It was tall and scraggly, but no blooms. Maybe next year.
Amy says
Sometimes it will not bloom in its first year. 🙂
jim stricker says
I was told that common milk weed attracts common flys . do you know if there is anything to that?//////////My common milk weeds are next to our deck that is attached to our house.
Amy says
I wouldn’t be too concerned. House flies are just one of many pollinators that are attracted to milkweed. They typically aren’t the dominant pollinator, and they don’t stick around for long.
pam says
My milkweed is covered with flies and wasps. I have also seen a significant amount of monarchs. I was just wondering if the flies and wasps are usually found in large numbers on milkweed.
Amy says
Yes, it’s normal for all types of pollinators to be attracted to the milkweed flowers.
Libby says
Hi Amy,
I am getting more and more into edible permaculture. Marie Viljoen, in her book Forage, Harvest, Feast says that she has only cooked with Common Milkweed, but that the other milkweeds, including Swamp Milkweed (Asclepias incarnata) are also OK to eat cooked. As Swamp Milkweed is less invasive, I would love to grow it and share it with monarch butterflies. I am having difficulty finding more evidence of its edibility by humans. Do you have any suggestions?
Amy says
I don’t have any information or resources that point to the milkweeds as being edible.
Brenda says
As far as I understand, the milkweed beetles are pretty harmless and you can leave them alone unless they are seriously damaging the plant. I’ve also recently learned that monarch caterpillars prefer young leaves to eat, so trimming back common milkweed is supposed to be one way to ensure you get eggs and caterpillars. I’ve got a pretty good patch of common milkweed in my yard but I never trimmed it so it gets really tall, falling over my sidewalk, and I never see eggs or caterpillars. I’m going to try trimming it (a few plants at a time, staggered over the growing season) to see if I can get smaller, more manageable plants as well as more caterpillars. I do have lots of flowering plants, so I frequently see monarch butterflies. Here’s hoping I can get the next step in their life cycle going!
Terry Harris says
I have a lot of common milkweed in my garden and I frequently get the milkweed buvs. I can’t stand them! Regardless as to whether they are harmful or not. Most of the time they are seen mating and when their eggs hatch, there are millions of those little bugvers! They can’t fly until they are adults, but grossly, I just pick them off and smash them. Also, I have been saving these guys for about 3 years now, and this is the 1st hear that I have had such a hard time finding older cats. As I mentioned I have a ton of milkweed and I have to go out really early to find babies and have a little success with some eggs. The wasps and the lizards are extremely thorough. I have wasps traps up, but they don’t help much. I cannot locate any wasp nest anywhere. I’m having the same problem with my passion flower plant. Last year I could count 20 or more gulf flitterary cats of various sizes on the plant, but this year’s I can’t hardly find one baby! I’m very discouraged with that effort.
Barbara Stavens says
I had two monarch cattapillars on my swamp milk weed. They were large. The next day one was missing and the other was at the bottom of the twig they both consumed. I placed it at the top of another full twig and got busy around the yard. When I went to check it out and hour later it was gone. I figured a bird must have eaten it. Also I noticed that flies are sticking to the leaves. And they are dried up carcuses. Can you tell me anything about that?
Amy says
Sounds like a predator such as a spider or preying mantis.