Regrow milkweed for monarchs: A citizen science study

If you have a patch of milkweed and some time, you can help study how to best conserve monarch butterflies.

New common milkweed stems emerge after being cut back
New common milkweed stems emerge after being cut back in mid-June. Photo by Nathan Haan, MSU Entomology.

Want to help monarch butterflies? With a patch of common milkweed and pruning shears or string trimmer, you can help Michigan State University scientists learn if managing common milkweed for mid-summer regrowth is a reliable way to increase monarch egglaying and caterpillar survival.

Monarch butterfly populations have been in decline for several decades and efforts to conserve them often focus on planting more milkweeds, the monarch caterpillar’s only food source. While access to milkweeds is critical for monarch reproduction, it is not enough. There are two more things that could help increase their numbers: 1) access to the right plant stages and 2) safe locations for eggs and caterpillars to grow and mature.

While monarch caterpillars feed on several species of milkweed, our citizen science study focuses on common milkweed (Asclepias syriaca). Female monarchs greatly prefer to lay eggs on young milkweed shoots, which are typically only present in May and June. These stems are more tender and may be more suitable as food for early-stage caterpillars, but they get harder for butterflies to find as the summer progresses. On top of this, once monarch eggs are laid, most last only a few days before being eaten by predators. We have been investigating both problems for several years and need your help to see if our findings can be more broadly useful in monarch conservation.

The potential solution we discovered is based on common milkweed’s remarkable ability to regrow after being cut back. Under most conditions, when a common milkweed stem is cut off near ground level, in about two weeks a new shoot will appear from the roots. These new shoots are highly attractive to female monarchs, receiving two to 10 times more eggs than older stems. In addition, regrowing stems harbor fewer predators, giving young monarchs a chance to grow. In our studies, survival of eggs and young larvae was two to 2.5 times higher on regrowing stems. We have observed that older stems are important, too. As caterpillars mature, they often move from younger stems onto the older ones, so it may be that maintaining diversity in milkweed stem age is key.

We now need your help to learn if these techniques will work under a wider variety of conditions. We hope to have participants from across the Eastern U.S. and Canada—anywhere milkweed grows and monarchs can be found during the summer months. You can participate in the study in several ways. If you have access to a single milkweed patch, cutting back one-half of the stems in early to mid-summer and monitoring the resulting egglaying will be helpful. If you have access to multiple patches, cutting back a portion of one patch and leaving the other patch unmanipulated would be even better. In either case, we will be providing detailed instructions on how to register your study sites and how to report your results.

Visit our website, ReGrow Milkweed for Monarchs, where you can sign up to participate and learn more about our monarch research. If you are unable to cut stems or wish to further assist identifying how milkweed supports specialist insects, MSU Extension is facilitating an additional project, the summer milkweed search, monitoring other insects that visit milkweed. Look for more information in an upcoming MSU Extension Gardening in Michigan news article.

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