If you grow Milkweeds to attract Monarch Butterflies, do you ever wonder why some plants get lots of Monarch eggs and caterpillars while others are ignored? This is the question, more or less, that some scientists tried to address with research published in the journal Frontiers in Ecology and Evolution.

Entomologists measured the number of Monarch eggs found on Milkweeds planted in different configurations with grasses and nectar plants.

Entomologists Adam Baker and Daniel Potter at the University of Kentucky measured the number of Monarch eggs found on Swamp Milkweed (Asclepias incarnata) scattered among grasses and nectar plants versus those planted around the perimeter. They also looked at Swamp Milkweed planted in a mass surrounded by grasses and nectar plants.

DSC_0821 monarch on swamp milkweed

The results were pretty clear:

… monarch eggs and larvae were 2.5–4 times more abundant in gardens in which the milkweeds were planted around the perimeter, surrounding the nectar plants and grasses, than when the layout was reversed, with milkweeds in the garden interior, or when the milkweeds were randomly intermixed with the other plants.

Monarch Butterfly on Swamp Milkweed.

Also notable:

Female monarchs foraging in an open-field setting laid significantly more eggs on single milkweed plants that were accessible from top to bottom, without visual obstruction, compared to single plants surrounded by, but not touching, ornamental grasses of equal height.

Another thing the researchers found: Monarchs are less likely to use Milkweeds located next to buildings that block north or south access. Turns out courtyards are an especially bad place to put your Monarch Waystation.

These results kind of confirm my own experience in the garden. I’ve been frustrated by the scarcity or Monarch eggs and caterpillars on my Milkweed plants. When I do see caterpillars they are on Butterflyweed plants (A. tuberosa) that have been planted on the perimeter of a bed or border.

DSC_0714 Monarch
Monarch on Butterflyweed.

I have a whole bunch of Swamp Milkweed and also some Prairie Milkweed (A. sullivantii) that’s scattered among other tall plants. These get no Monarch eggs at all, though they are used for nectar.

After reading this article, I will try to encourage Milkweeds to take over space along the edge of some of the borders. This is feasible mainly along the back of the Sidewalk Border and along the west edge of the Front Island Bed.

Anyhow, read the article yourself. The writing is a bit dense, but not impenetrable. Does this research fit with your own experience with Monarch eggs and caterpillars?


32 Comments on “How To Get Monarch Eggs On Your Milkweeds”

  1. I think this is fascinating information. I have always wondered why Monarchs don’t use my butterfly weed. It is mixed up in plantings. I will have to find someplace else for it. I am glad you shared this study. I will read it for more info.

  2. Interesting! I think I get the most eggs along the path that cuts my garden in half. I also have a raised bed along my driveway with swamp milkweed that is frequented, too. However the milkweed at the far side of the garden intermixed with shrubs is hit and miss. Sometimes it has eggs- sometimes it does not.

  3. Here the only thing I can say for sure is that butterflies of all kinds including Monarchs avoid shaded areas. They fly around them. I can only guess they need the direct warmth from the sun? I had some California native milkweed planted by itself in a sunny open area but the butterflies avoided it because it is surrounded by shaded areas.

    We had a whole lot of Monarchs in ’17, but very few this year and last. No shortage of milkweed aphids!

  4. Thanks so much for sharing this valuable research. I’ve let the common milkweed put itself where it wants to be in the “meadow-ette”, editing for practical and aesthetic reasons. That editing, now that I think back on it, has meant fewer milkweeds right at the edge and more scattered in the interior.

    Will bear in mind next spring — but deer may have the last word: to my amazement, in early June they ate all but one of the plants down to a foot. It was the first time, and maybe will be the last, because the milkweed and everything else was unusually succulent after a wet fall, winter, and spring.

  5. I’m in Canada and my most prolifically laid on plant is in the shade right against my house. It is my oldest stock (in years) and once when I had to stop collecting that my plant had 25 eggs on it I week. I have noticed tons of milkweed never has eggs on it in fields however.

  6. Thanks for sharing! That fits with what I see in my garden. It seems like I inadvertently created an ideal situation by putting milkweed plants along the fence between my yard (full of nectar plants) and my neighbors’ yard (basically just a lawn).

  7. Hi Jason! This is so interesting. I saw someone share it a couple weeks ago and have been meaning to come back and read the whole thing. Thanks for finding it and summarizing it for us! I saw a behavior this summer that might be similar to what the researchers observed, though I saw it only once, and with a differently butterfly and host plant.

    There is a large area I spent several weeks converting from Japanese stiltgrass into a wildflower garden. It had been previously mowed for years, but this past spring and summer I noticed an abundance of violets and native sedges growing among the stiltgrass. So I began pulling the stiltgrass by hand and leaving the violets and sedges. Well, within half an hour of starting this project, I was joined by a variegated fritillary butterfly, and she went to each and every violet that was now exposed and freed from its stiltgrass prison!

    This went on for a few minutes, and about six weeks later I found one of her caterpillars in the violets. What was fascinating was that the mama butterfly did not go to the violets that were still buried under the stiltgrass just a few feet away (and there were tons of violets there as well). She only visited the ones she could easily see or access (at least that was my interpretation of what she was doing). I guess it makes sense that any creature is going to take the quickest and most productive, energy-saving path of least resistance.

    I got videos of both of these things happening, but I may have posted them only on social media and included in my talks. Maybe I will write a post this winter about it, and I can link to your summary of this study!

    Also, we spent Thanksgiving with my parents-in-law in Scottsdale and went to Taliesin West too! We are there every year but have never seen it, as I usually prefer the outdoor adventures as well. But it was really fascinating! Too bad our paths didn’t cross. Happy New Year!

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