The Monarch Butterfly Population is in Decline – But You Can Help!

There is a psychological phenomenon that makes it difficult for humans to notice slow changes. Our brains adjust to the new reality without noticing; and we don’t perceive what is missing until something reminds us how things used to be.  As spring washes over the Chicagoland area, most of us will not notice that it has become quieter. There are fewer buzzing insects and calling birds. There are also fewer monarch butterflies. It may be hard to believe, but this familiar and colorful butterfly has declined to the point that the monarch is now a candidate for the endangered species list.

The monarch butterflies we see in Chicago migrate annually between southern Canada and central Mexico, they are a part of what we call the Eastern Population, separated from the Western Monarch population by the Rocky Mountains. The Eastern population has decreased from 384 million recorded in 1996 to less than 60 million in 2019, an 85% decline.

Because most of the Eastern monarchs congregate at known wintering grounds in central Mexico, the populations are counted in hectares where they overwinter in tight groups on oyamel trees. In 1996, monarchs occupied over 18 hectares; however, in the winter of 2020/2021, the population area had fallen to less than 2.1 hectares (Figure 1).* Several factors contribute to this decline, but one that we as individuals can address is a national lack of milkweed, the exclusive source of food for Monarch caterpillars.

What can you and I do to protect this imperiled population?

Chicago and the Midwest play an important role in the migration of the eastern population. In June, monarchs will arrive in the Chicago area on their return journey from central Mexico. Here, they will breed and lay eggs only on native plants in the Asclepias genus commonly known as milkweed. 

Throughout the summer, generations of monarchs will reproduce in the Midwest, eventually spawning a super generation that will migrate back to Mexico in late August/early September. The U.S. Fish and Wildlife Service noted that in order to preserve the butterfly and its notable migration, 1.8 billion stems of milkweed need to be added to the eastern United States landscape, declaring an “all hands on deck” approach with active participation of different agencies, states and stakeholders. And of course, individuals like you! Research from the Field Museum has shown that urban areas like Chicago can make an important contribution to that number.

However, while we know cities can provide a habitat and a substantial piece of the 1.8 billion stems of milkweed we need, we are unsure which patches of urban habitat attract monarchs, drawing them to lay eggs, and are most effective in completing its lifecycle. The presence of milkweed plants is definitively the most important component, as monarchs only lay their eggs on, and their caterpillars only eat, milkweed.  

But not all urban milkweed oases are equally effective. Research indicates that while a single milkweed plant can attract butterflies and provide a food resource to caterpillars, the placement of patches, layout of plants, size, nectar availability and other attributes might also play an important role. To answer these questions, we need a lot of data from many urban patches varying in size, locale, and composition. This is where our group is asking the help of community scientists – help from individuals like you!

How you can work with the Field Museum as a community scientist

To determine what makes a successful urban patch, the Keller Science Center at the Field Museum has been working with citizen scientists for the past two years.  For the summer of 2021, once again our group is actively recruiting Monarch Community Science volunteers to continue our research and help us understand more about how monarchs use urban milkweed habitats.

Along with participating in our virtual training sessions (focusing on how to recognize the various species of milkweed, and stages of development in monarch caterpillars), all you need is internet access (to report your data) and at least one milkweed plant growing in the ground or in a pot in your yard, balcony, rooftop, or other location you can visit weekly. If you do not have a milkweed plant, participants will be able to receive milkweed that’s best suited for their garden conditions.

We ask that participants observe the same milkweed plants once a week and count the number of eggs and caterpillars that they see, record the data, and submit it. The information you provide will help us better understand why some milkweed patches are more attractive to monarchs then others.

For example, data from our 2019 and 2020 volunteers help us understand the patterns of egg laying throughout the summer. As you can see, our volunteers recorded substantially more eggs in July then either June or August (Figure 2).

Figure 2: Eggs observed on Milkweed plants, 2019 and 2020. 72 volunteers participated in 2019 and 179 in 2020.

Community scientists that are active in the program will be able to pick up milkweed plants in June from our group at free plant distributions in June. There is a milkweed species appropriate for almost any setting, from common milkweed (Asclepias syriaca) that is easy to establish but somewhat aggressive, to more cooperative species that will stay put and add texture, color, and fragrance to your space. These include swamp or rose milkweed (Asclepias incarnata), best suited to wet and sunny to part sun conditions, and butterflyweed (Asclepias tuberosa), a good choice for drier soil.

Picking the appropriate plant that can grow in wet or dry conditions, full sun, or part shade will ensure success for both you and the butterflies. And while a larger area may be more likely to attract monarchs, even a planter on a balcony can successfully attract monarchs (and other pollinators.)  For a more complete list of milkweeds in this region please consult this field guide.**

Of course, monarch butterflies need a lot more than just milkweed plants.  Milkweeds are crucial in the larval stage (the caterpillars feed only on these plants), but adult butterflies need other flowers to collect nectar for energy and nutrients. That means that to support the adult butterflies, we need to give them access to blooming flowers when they are in the area – mainly from June to late September. (Having flowers in bloom from April through October is a great rule of thumb. That way, the garden attracts and supports many other pollinators).

Native plants – plants that have evolved in this region for thousands of years and are adapted to survive our freezing winters and scorching summers – are a great choice for any space big or small. Those prairie, savanna and woodland plants come in different heights, shapes, colors, and blooming times and can be arranged in beautiful designs in any garden. Although native plants are hard to obtain in big box stores, you can visit any number of  native plant sales, where you can purchase appropriate flowering plants, or you can visit any plant nursery throughout the Chicago area

What else can you and I do to protect pollinators?

Besides taking part in our 2021 Community Science Research project, there are other things that you can do to help the monarch and other pollinators. For one, you can reduce your use of pesticides and herbicides on your property and encourage others to do so. One group of pesticides that is particularly problematic for pollinators is the Neonicotinoids, because they embed in plant tissues. Some flowers sold at nurseries have been pretreated with this chemical, so it is good to check before adding these to your pollinator garden.

Monarch butterflies need more than any one garden to survive, especially as they make their migration.  Let us all work to convince our elected officials to get involved in conservation though small local actions like signing the mayor’s monarch pledge, to state-wide and national efforts that allow us to approach the problem holistically. One of the best gifts we can leave to future generations is a world rich in biodiversity, a resilient web of life, and the symphony of songbirds and cicadas, of woodpeckers and crickets, that play each spring. And of course, the appearance of the iconic monarch. Sign up here for our monarch community science project.

*The smaller Western population has experienced an even greater 99 percent decline, to fewer than 2000 individuals observed in November of 2020

**Non-native tropical milkweed (Asclepias currasavica), often available in big box stores, should be avoided in favor of species native to your region.

Header image by Mark Rogovin