Plant milkweed!
Field
Museum
Monarch
butterflies, with their striking orange and black wings, are some of the most
recognizable butterflies in North America. But they're in trouble. Monarch
caterpillars can only eat the leaves of milkweed, a native wildflower. These grow naturally in Charlestown RI.
RI has eight native species of milkweed
As milkweed has disappeared, so have the monarchs, to the point that they're at risk of extinction. Research shows that planting milkweed in home gardens can add significant monarch habitat to the landscape.
In a new study in the
journal Frontiers in Ecology and Evolution, researchers and
community scientists monitored urban milkweed plants for butterfly eggs to
learn what makes these city gardens more hospitable to monarchs. They found
that even tiny city gardens attracted monarchs and became a home to
caterpillars.
“In this study, we found that monarchs can find the milkweed, wherever the milkweed is, even if it’s in planters on balconies and rooftops,” says Karen Klinger, a Geographic Information Systems analyst in the Keller Science Action Center at the Field Museum and the study’s lead author. “Milkweed gardens can be in all shapes and sizes, and any milkweed garden can contribute habitat for monarchs.”
Monarch
butterflies have one of the most unusual and demanding migration patterns of
any insect. The eastern population of monarchs starts the year in Mexico, and
they move up across North America in the spring and summer. “As they travel,
they lay their eggs, and when those adults die, the next generation continues
the migration northward. They will make it all the way to southern Canada, and
at the end of summer, a new super generation is born that migrates all the way
south and survives through the winter,” says Klinger.
Since
it takes multiple generations of milkweed-eating caterpillars to get the
monarch population from Mexico to Canada each year, the monarchs rely on
milkweed plants throughout their migration path. “There used to be wild
milkweed growing along farmland in the Midwest, but now farmers use pesticides
that kill the milkweed. As a result, a lot of the habitat for monarchs in the
Midwest has disappeared,” says Klinger.
Monarch
populations have declined along with the disappearance of milkweed; in recent
years, they’ve been a candidate for endangered species status by the
International Union for Conservation of Nature and the US Fish and Wildlife
Service. “ If we don’t do anything soon, monarchs are going to be in serious
trouble,” says Aster Hasle, a lead conservation ecologist at the Field Museum’s
Keller Science Action Center and a co-author of the paper.
Since
so much of the rural milkweed that monarchs used to rely on has disappeared,
scientists have wondered if milkweed gardens in urban areas might be able to
bridge the gap. “There was a call for all hands on deck, to plant milkweed
across all sectors of the landscape, but people discounted urban areas, because
if you look at some mapping of urban areas, it looks like it’s completely
developed, with no availability for milkweed plants,” says Klinger.
Klinger
was a co-author of a 2019 study led by Field Museum scientists that showed that
even “concrete jungles” have room for milkweed plants, in people’s yards,
alleyways, and rooftops.
The
new study led by Klinger is a follow-up to this earlier work. “With our 2019
study, we found that a lot of the spaces where milkweed could grow was
inaccessible to scientists-- we couldn't go into people's backyards, and look
at their milkweed, so there was a lot of milkweed that we can't account
for,” says Klinger. “But we also found that there was a lot of enthusiasm among
residents to plant milkweed and support monarchs. So based on that, we did a
community science project that became the basis of this new paper.”
Klinger
and Hasle worked with volunteers around Chicagoland to monitor milkweed plants
in their yards and neighborhoods for monarch butterflies laying their eggs on
the plants and caterpillars eating the milkweed leaves.
“We
wanted to answer the question of, how well do these urban milkweed gardens
actually support monarch butterflies? Everybody always wants to know, what
should I plant? What species of milkweed, how many plants, how big of a garden?
There are so many questions to answer, so we were hoping that we could use this
project and the data from it to start answering those questions.”
Klinger
and Hasle trained over 400 community scientist volunteers on how to monitor
their milkweed for monarch eggs and caterpillars, which they reported back to
the researchers. Over the course of four years, the team collected 5,905
observations of monarch activity on 810 patches of milkweed in Chicagoland.
This paper analyzed a portion of this data from 2020-2022.
“We
encouraged participants who had planters on balconies, who had planters on
rooftop decks, and we saw some of the most amazing things,” says Klinger.
“There was one participant who had a planter set on the condominium roof that
had five large caterpillars in one photo.”
Based
on these observations, the researchers found several overarching trends about
what makes for a successful milkweed garden. “There are several native species
of milkweed, and we found that common milkweed was very prevalent in people’s
gardens and was really key, both in terms of whether monarchs laid their eggs
there, and how many they laid,” says Klinger. “Also, kind of surprisingly, that
older, more established milkweed plants did a lot better, they were more likely
to see eggs than younger plants.” In addition, having a variety of blooming
plants was also key for monarchs to lay more eggs on milkweed, as it provided
lots of nectar for the adults.
However,
while a garden with lots of native milkweed and other flowering plants left to
grow year after year might be the best way to help monarchs, the researchers
noted that every little bit helps. “Plant the species that works the best for
you and your garden,” says Klinger. As of July 24, 2024, Illinois Governor JB
Pritzker signed into law the Mobilizing Our Neighborhoods to Adopt Resilient
Conservation Habitats (MONARCH) Act, which restricts HOAs from prohibiting
native plantings and provides financial and technical assistance for
establishing native and pollinator-friendly gardens.
While monarchs are just one small species of insect, they're indicative of the big-picture health of the ecosystems they live in. “Because they cross this big landscape from Mexico to Canada, monarchs are an important indicator of what's happening across a big area,” says Hasle. “Monarchs need a lot of the things that other insects need, like blooming flowers, so what’s good for monarchs is good for other pollinators too. And we’re in the midst of a global insect decline, so it’s important to help.”