Monarchs and Milkweed
submitted by Meaghan Rondeau, Naturalist Goodwin Conservation Center
Monarch Butterfly (Danaus plexippus) and Common Milkweed (Asclepias syriaca)
In late June and early July in eastern Connecticut some of our most beautiful native wildlife starts to appear: monarch butterflies.
Monarch butterflies are one of the most well-known and appreciated butterflies in the United States. Within the U.S. there are two regionally distinct groups of monarchs: the western monarchs and the eastern monarchs. They are the same species; the only difference is in their range. The two groups are split by the Rocky Mountains. Western monarchs breed west of the Rocky Mountains while eastern monarchs breed east of the Rocky Mountains (pretty easy to remember, right?).
But that’s not all, the two groups overwinter in different locations as well. Monarchs are famous for their yearly migration to Mexico, but the eastern monarchs are actually the only group that travels to Mexico. Western monarchs overwinter in Southern California-- close to Mexico, but not quite over the border.
Additionally, while monarchs are only native to the Americas, they have spread across the globe and now reside in many subtropical areas of Europe, Oceania, and Africa.
Despite their shocking range, both western and eastern monarch populations are in a steep decline. While not yet on the endangered species list, there has been significant push in the last decade to have the species evaluated and given a protected status. Among the greatest threats to monarchs are habitat loss and climate change.
The loss of milkweed habitats for caterpillars to grow on has been detrimental to the species. Monarch caterpillars only eat milkweeds, and while the U.S. does have many native milkweed species, they are commonly mowed down in both agricultural fields and on roadsides. Milkweed contains a toxic latex that can be poisonous to cattle if consumed in large enough amounts, so the fields where milkweed prefers to grow, are often systematically cleared of the plant for the protection of the cattle. And, along roadsides where the plants also flourish, roadside mowing and herbicides destroy valuable habitat. While protecting cattle and keeping roadsides clear is important, the destruction of habitat without providing safe growing space has led to the staggering decline of monarch butterflies.
Climate change is another threat that monarchs, like most species, must face. Changing global temperatures and weather patterns disrupt the breeding and migration patterns of monarchs. Extreme weather can wipe out huge populations of monarch butterflies, caterpillars, and milkweed. And unseasonably cool or hot temperatures can cause mass die-offs of the delicate animals.
Migration is vital to the life cycle of monarch butterflies. They breed in the northern parts of the U.S. but with the arrival of cool fall temperatures, they must journey south where they will be warm enough to survive the winter. The western population travels just along the west coast of North America, travelling north to breed and then south to overwinter. The eastern population breeds in the northeast U.S. and eastern Canada, then migrates to central Mexico. When we see monarchs appear in the early summer, they are returning from their tropical Mexican holiday.
Right now, they are reproducing as they work their way north. A single butterfly does not make the whole north-bound Mexico to Canada journey, instead, four or five generations will take place as one genetic line travels up and down the coasts. Each generation grows from egg to butterfly, quickly reproduces, and then continues north. The growth process, from egg to adult, takes two weeks to a month depending on weather and temperature. The eggs take less than a week to hatch--if they aren’t eaten by predatory insects first-- and then the caterpillars will gorge themselves on milkweed, quickly growing from the size of your eyelash to your pinky finger. They go through five in-star phases, or sheds, during this process. When they reach this size, they find a safe place to hang from and form a delicate chrysalis. Over the next two weeks’ time they will transform into an adult butterfly. Once they emerge they dry off their wings and then get to work finding food and creating the next generation of monarchs. The reproducing adults live for just two to five weeks.
At the end of the summer or beginning of fall, the last generation hatches. These late bloomers are the travelers of their family, traveling up to 3,000 miles back to the warmth of the Mexican mountains. They will live for up to nine months-- plenty of time to stay warm all winter and begin the journey north again to mate. It is important that the butterflies have plenty of nectar food sources one their journey to Mexico, because once they arrive they do not eat anymore until they leave in the spring. They survive off their body fat and water from dew. They are very inactive during their overwintering period and do not need additional food for energy.
To help support monarchs, and other native pollinators, there are several things you can do.
At your home, school, or business, consider planting a butterfly garden. For monarchs in particular, make sure to include at least one of our native milkweeds: common milkweed (Asclepias syriaca), swamp milkweed (Asclepias incarnata), or butterfly weed (Asclepias tuberosa). Other plants that provide an excellent nectar source are: golden Alexanders (zizia aurea), wild bergamot (Monarda fistula), black-eyed Susans (rudbeckia hirta), coneflowers (Echinacea spp.), anise hyssop (Agastache foeniculum), Joe-pye weed (Eupatorium maculatum), and goldenrods (Solidago spp.). Make sure that the plants you choose are appropriate for the location--if you need help, many options are available online or you can reach out to a local garden club or your local extension service.
If you own or know of an area where healthy milkweed grows every year, that isn’t mowed or sprayed with pesticides or herbicides, consider creating a registered “Monarch Waystation” through Monarch Watch, a monarch conservation program. Not only are these great for monarchs, but they’re incredibly valuable in increasing public awareness about the importance of milkweed habitats for monarchs.
If you are a farmer or maintain land where milkweed grows, consider looking into alternative maintenance methods that don’t involve removing milkweeds, or create new areas of milkweed to offset the loss and support migrating monarchs.
And, if nothing else, be a monarch advocate. Spread the word about the importance of maintaining healthy milkweed and monarch habitats so that monarchs will continue to be a beautiful presence in Connecticut every year.
Here are some helpful links with additional information:
Monarch watch: https://www.monarchwatch.org/
Audubon tagging: https://www.ctaudubon.org/2019/09/tagging-monarchs/
Life cycle diagram: https://www.fs.fed.us/wildflowers/pollinators/Monarch_Butterfly/biology/index.shtml#:~:text=The%20monarch%20butterfly%2C%20like%20other,(chrysalis)%2C%20and%20adult.
Monarch biology: https://monarchjointventure.org/monarch-biology/life-cycle/adult
Weekly migration news: https://journeynorth.org/monarchs
Milkweed and monarchs: https://www.nwf.org/Garden-for-Wildlife/About/Native-Plants/Milkweed
Milkweed biology: https://www.fs.fed.us/wildflowers/plant-of-the-week/asclepias_syriaca.shtml
Milkweed biology 2: https://plants.usda.gov/plantguide/pdf/cs_assy.pdf
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