Monarch butterfly 2017 update in Michigan
Monarch populations are increasing in Michigan, but they are still low due to factors including milkweed quality and predators. We are interested to hear if you’ve seen organisms preying on monarch eggs and caterpillars.
October 5, 2017 - Author: Douglas Landis, Michigan State University Extension, Department of Entomology
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The fall migration of monarch butterflies is well underway and butterflies are currently winging their way south to where they winter in central Mexico. Many people in Michigan reported seeing more monarch butterflies this summer. Since more butterflies were reported to have arrived and survived in Mexico last year, an increase in this summer’s population makes sense. Monarchs mass together in specific Mexican forests and reportedly covered approximately 7.2 acres of forest in the winter of 2016-17. This is up from extreme lows of 1.7 – 2.5 acres in the winters of 2013-14 and 2014-15. However, it is still well below the goal of 14.8 acres set by the U.S., Canadian and Mexican governments.
While increases in overwintering butterflies are encouraging, monarchs still face many difficulties. The forests where they collect are continually threatened by illegal logging. Also, the area monarchs travel over in North America is being used in ways that leave fewer flowers with nectar when more is needed. Monarchs must have a steady supply of nectar along their fall migration path to build up the fat they live on during winter when they do not feed. Some years droughts dry up flowering plants. Negative impacts from pesticides and increased disease in monarch butterflies are additional concerns. Finally, in our area where summer breeding occurs, there are fewer milkweeds, the critical host plant for monarch caterpillars.
Ongoing research in our lab is exploring how milkweed quality and predation influences where monarchs lay eggs and whether they survive. Our long-term goal is to be able to recommend practices for improved care of monarch habitats that will result in greater egglaying and increased survival, contributing to monarch conservation.
In our research this summer, we observed the first monarch butterflies and eggs in May in the Lansing, Michigan, area. While there were few butterflies in June, their numbers increased in July and August. In our experiments, monarch egglaying peaked the first two weeks of August then declined. Many observers noted they saw fewer eggs and caterpillars compared to what they recalled in the past. Our data from 2017 indicates monarch eggs and caterpillars can still be hard to find despite reported increases. We monitored 240 stems of healthy common milkweed per week at eight different sites around Lansing from June 13 to Aug. 24. During those 11 weeks, we found only 15 eggs and 16 caterpillars on the 2,640 stems we observed, and only six of those were fully grown caterpillars.
We did find many potential predators of monarch eggs and caterpillars. About 50 percent of the stems we observed held potential predators, averaging two to three per plant. By far, the most abundant of these were ants, followed by an assortment of predacious lady beetles, spiders, true bugs, wasps and earwigs. Our observations also confirmed that some insects we normally think of as plant-feeders will readily eat monarch eggs and caterpillars when given the opportunity. These include grasshoppers, crickets, katydids and mirid plant bugs.
Tell us, have you seen predators feeding on monarch eggs or caterpillars?
Our observations got us wondering, have you ever seen insects or other organisms preying on or harassing monarch eggs and caterpillars? If so, we would be interested in learning from your observations. If you have seen events of monarch predation or harassment, please send us a quick description, or better yet, a photograph. Unfortunately, we will not be able to respond to all your comments, but your efforts will help inform what other species prey on monarchs and should be considered in our research. Send your observations or photos with a brief description to email@example.com.
Dr. Landis’ work is funded in part by MSU’s AgBioResearch.