Monarch (Danaus plexippus) sightings across the country are expected to be rarer this September and October. Scientists noted a significant drop in migration numbers for the beloved butterflies last year.
Experts point to habitat loss and climate change as major contributors to their significant population decline.
Monarchs: Beloved visitors and harbingers of fall
During the long, warm days of summer, adult monarchs’ instincts tell them to fly north and find more milkweed to start the next generation. As fall brings shorter days and cooler weather, they stop reproducing and begin the journey to their overwintering grounds in Mexico. This yearly trek stretches several thousand miles from the Southern Canada to Mexico.
For centuries, millions of monarchs have migrated to Mexico each fall, making stops along the way and delighting communities with their annual visit. At one point, the mass of migrating monarchs even appeared on doplar radars.
Monarch caterpillars only eat milkweed (Asclepias) plants, but adult monarchs feed on flower nectar. Monarchs attempting to migrate need a constant source of nectar during their entire journey.
Asters, goldenrods and other native wildflowers that bloom during the fall months provide this nourishment.
Once the monarch emerges, the next generation continues the journey south.
A Historic and alarming Monarch Population Decline
The familiar sight of monarchs is becoming rarer as habitat loss and climate change leave fewer places for these monarchs to rest on their journey.
During the 2023-2024 overwintering period, scientists noted a 59% decrease in the population size from the previous year. This is the second smallest overwintering population ever recorded.
For butterfly lovers and entomologists, this news was disheartening.
“The numbers have been fluctuating so much over the last couple of decades that, although I was not expecting this news, I am also not incredibly surprised to hear it either,” says Yankoski. “This reinforces how important it is to act swiftly to protect migrating monarchs while we still can.”
Insect populations naturally go through peaks and valleys. In fact, it was only relatively recently that entomologists discovered the overwintering grounds in Mexico. Because of this, we only have around 31 years of solid data about the size of the overwintering monarch populations.
Because this data set is relatively small it is impossible to say with certainty how much of an anomaly the decline was.
Monarch habitat destruction and climate change
“If you look at the trends in the data over the last 30 years it is pretty alarming,” says Yankoski. “For the first 10 years the size of the overwintering monarch population was measured, it averaged 21 acres. For the last 10 years the size is a bit under 7 acres, a decline of two thirds, which is cause for alarm.”
Yankoski and many other scientists point directly to habitat loss, not only at the final destination in Mexico but also in the Heartland, as a major reason for the population decline.
“Illegal logging and deforestation at their overwintering grounds has led to extreme temperature fluctuations that have killed off millions of butterflies in a single storm,” Yankoski said. “Climate change has led to nectar plants blooming at different times than the historical norm, and as a result migrating monarchs miss the peak bloom period and pass through areas without enough flowers to feed them.”
Why Should you Care About Monarchs?
Even if you are not a fan of monarchs (or maybe even have lepidopterophobia), you should take note of the rapid decline in the monarch population. It is a sign of more ecological bad news.
Yankoski says the monarch butterfly’s decline shines a light on a much bigger problem than a single butterfly species.
“It is important to remember that when highly visible species like monarch butterflies are in decline, the same things affecting them are likely negatively impacting thousands of other species,” Yankoski says. “Insects are very adaptable and resilient, and we should take note when they are struggling instead of thriving.”
Conservation efforts to save the monarch are, at their core, habitat conservation efforts which will protect pollinators like bees and butterflies. It also protects other insects like grasshoppers or caterpillars that play important roles in the food chain.
Are Monarch Butterflies a Protected Species?
The nosedive in overwintering monarch populations is grabbing the attention of the scientific community.
But the question of whether monarchs are endangered – and whether their habitats should be protected – is yet to be officially decided.
In 2022, IUCN Red List of Threatened SpeciesTM classified monarchs as “endangered” for the first time. But just over a year later, the IUCN downgraded monarchs to “threatened” after more scientific research was presented. This decision was made before data on the 2023/24 drastic decrease in overwintering monarchs was collected.
Some scientists say an official marker of endangered by the IUCN would help the case for monarch habitat protection, but it is ultimately the U.S. Fish and Wildlife Services (USFWS) that would make decisions for protection under the Endangered Species Act.
Monarchs are not currently listed under the Endangered Species Act, but the USFWS is currently re-evaluating the monarch’s status. Many entomologists and monarch-focused nonprofits are waiting to see if the agency will announce a proposal to add monarchs to the list of protected species by the end of 2024.
“The Butterfly House will continue to promote pollinator-friendly insect conservation practices regardless of the decision,” said Yankoski.
The Butterfly Species with A similar situation
While the decision of whether to issue government protections of monarch habitats is yet to be made, another butterfly found in Missouri was proposed for protection earlier this year.
In August, the USFWS proposed that both subspecies of Regal Fritillary Butterfly be added to the list, including the western regal fritillary found throughout the Midwest and Great Plains.
The independently peer-reviewed species status assessment cited issues familiar to those already working on monarch conservation projects. This included habitat loss, agricultural and urban development, pesticide use, invasive plants, climate change, drought, local climate events and collection as issues leading to regal fritillary decline.
What you can do to help monarchs
Monarch butterfly conservation is tricky because their natural history is so unique. Every single year their range is spread out over thousands of miles with many different challenges.
But don’t despair, you can still help monarch butterflies and other native pollinators locally. Studies of nectar availability in cities have shown that over 80% of the available nectar comes from planted gardens, not wild plants.
So what can you do to help monarchs and other native insects?
Plant native wildflowers
Native insects have adapted to live with native plants for millennia and rely on them for food and shelter. Monarchs and other pollinators need nectar sources all year long, but for monarchs, plants that bloom in the fall are especially important. Fall-blooming nectar plants fuel their migration, and the Midwest is right in the heart of the migration pathway.
Discover More: Native Plants Monarchs Love
Plant host plants
Host plants provide food for butterfly caterpillars. For monarch butterflies that is milkweed, but you can plant host plants for other native butterflies, too.
Reduce or eliminate pesticides
Pesticides are very good at killing insects, but many kill indiscriminately. Someone may see a single ‘bad bug’ in their flowers and spray pesticides to kill it. But some pesticides stay lethal up to a month after spraying and are just as likely to kill butterflies, bees, ladybugs, or other important insect species – even ones that show up days or weeks later.
Reduce lawn mowing and leave the leaves
Flowers like dandelions or clover, that many might consider a weed, provide an important food source for hungry insects like bees or butterflies when resources are otherwise limited. Many insects also overwinter in leaves, in plant stems, or under bushes, and allowing leaves to stay on the ground until spring provides homes for insects like bumblebees, ladybugs, or even butterflies riding out the cold winter months.
Get involved in Project Pollinator at the Butterfly House
The Butterfly House has a program called Project Pollinator that is dedicated to helping all pollinators, including monarch butterflies, in the St Louis region.
Jessika Eidson | Public Information Officer
Thanks to the entomologists at the Sophia M. Sachs Butterfly House – Tad Yankoski, Chris Hartley, and Nicole Pruess – for their expertise on this topic.
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