Updated date:

Why Are Monarch Butterflies in Danger?

Jennifer is an environmentalist from Ohio. She is passionate about advocating for the planet and wildlife through gardening and education.

Why are monarch butterflies in danger, and what can we do to protect them?

Why are monarch butterflies in danger, and what can we do to protect them?

Why Monarch Butterflies are Important

Monarch butterflies are important pollinators in our ecosystem. Without pollinators, we humans, and most other animals, wouldn’t have much of the food we rely on for survival. Pollinators such as monarch butterflies are a vitally important part of the food chain. Butterflies are important indicators of the overall health of the environment and ecosystem where they reside.

Additionally, monarch butterflies are considered a “flagship” species for conservation. This means that they are a well-known, well-liked, and easily recognizable species that people are more willing to get involved with conserving. These butterflies help to get people involved in efforts to protect and restore habitats, which benefits not only monarchs, but other pollinators as well. Simply put, these butterflies inspire people to help protect the environment.

Unfortunately, these iconic pollinators are in danger, in no small part due to human influence. Because of human activities such as agriculture, pesticide use, urban development, and pollution leading to climate change, monarch butterfly populations are in rapid decline. Here are some of the biggest threats faced by monarch butterflies, and what we can do to help them before it is too late.

Climate Change

Because monarch butterflies are a migratory species, they are especially vulnerable to the effects of climate change. Their seasonal movements are regulated by environmental conditions, so any change in weather patterns due to climate change threaten their survival. Increased temperatures and changing precipitation patterns create environmental conditions that monarchs are not well adapted to, which can upset their natural migration schedule.

In the last decade, climate change has resulted in extreme weather patterns, including severe temperature changes, out of season storms, and excessive rain. These weather changes have proven deadly for monarch butterfly populations that rely on certain environmental conditions for survival and predictable seasonal changes for the timing of their migrations.

A monarch butterfly on a swamp milkweed next to my house.

A monarch butterfly on a swamp milkweed next to my house.

Loss of Milkweed

Though adult monarch butterflies can feed on the nectar of many different flowering plants, milkweed is the only food source that monarch caterpillars can eat, and as such, it is the only plant where female monarchs will lay their eggs. Milkweed plants are often destroyed as a result of urbanization and industrialized agriculture. Milkweed is considered a weed by many farmers, so it is destroyed in favor of profitable crops.

Over 90 percent of the grassland ecosystems that the eastern monarch population relies on has been destroyed for agriculture and urbanization. Extensive herbicide use by the agriculture industry has destroyed much of the milkweed plants that monarchs need for reproduction, as well as nectar plants used as a food source by adult monarchs. Without enough milkweed growing along their migration routes, monarch butterflies are unable to lay their eggs to ensure the continuation of their species.

Monarch migration map showing yearly monarch butterfly movement by generation. It takes four generations of monarch butterflies to make the complete journey each year, which is why it is so important to plant milkweed along migration paths.

Monarch migration map showing yearly monarch butterfly movement by generation. It takes four generations of monarch butterflies to make the complete journey each year, which is why it is so important to plant milkweed along migration paths.

Winter Habitat Loss and Fragmentation

As a migratory species, monarch butterflies rely on finding suitable habitat all along their migratory path. Unfortunately, this habitat has become fragmented as humans continue urban and agricultural development.

The eastern monarch butterfly population migrates south to the mountains of central Mexico every fall, where they overwinter. The western population, on the other hand, migrates west to the California coast during this time. Both of these monarch populations are facing the threat of habitat loss in their respective winter retreats. Winter monarch habitats in both Mexico and California are rapidly shrinking due to climate change, deforestation, expanding agriculture, and other human activity.

Yearly monarch butterfly migration patterns in North America: 1) March 2) April 3) End of April 4) April - June 5) June - August 6) September - November

Yearly monarch butterfly migration patterns in North America: 1) March 2) April 3) End of April 4) April - June 5) June - August 6) September - November

Pesticide Use

Pesticides, including herbicides that destroy the plants monarchs need to survive and insecticides that kill monarchs themselves, are one of the most significant threats that the species faces. Pesticides contribute extensively to habitat loss, disrupt the development of monarch caterpillars, and outright kill both adult and juvenile monarchs.

Pesticide use in fields near monarch habitats directly contribute to the decline of monarch populations. A study by Iowa State University (ISU) found that chemical drift from specific pesticide chemicals used in agriculture has a detrimental effect on the development of monarch caterpillars:

Results of the study found that dermal and dietary exposure to beta-cyfluthrin and chlorantraniliprole was most toxic to monarchs, and resulted in high levels of larvae stasis and mortality. Notably, neonicotinoid exposure uniquely halted monarch ecdysis (molting) and pupation from caterpillar to butterfly. ISU researchers estimated the greatest larval mortality to occur 0 to 15 meters (m) downwind of pesticide-treated soybean/maize fields. Aerial pesticide applications extended larval mortality range to 60m downwind of treated fields compared to boom pesticide spray applications. This study demonstrates that data and field-scale mortality estimates will help scientists elucidate the impacts of pesticides on monarchs and establish sustainable habitats.

[…]

This study indicates that pesticide exposure indirectly affects monarch populations by interrupting larval development and success rate. The reproductive success of monarch butterflies depends on milkweed availability as monarchs require milkweed to complete its lifecycle. Milkweed acts as an obligate host for monarchs to exclusively lay their developing larvae on leaves and stems. Researchers suggest planting an additional 1.3 to 1.6 billion milkweed stalks will improve monarch butterfly resilience. Milkweed grows most successfully on agricultural land, yet the study finds that pesticide drift from adjacent maize and soybean pastures threaten the obligate host’s survival.

A cute little monarch caterpillar on one of my swamp milkweed plants.

A cute little monarch caterpillar on one of my swamp milkweed plants.

What You Can Do to Help Monarch Butterflies

The best thing you can do to help monarch butterflies is to create your own “monarch waystation” (or small patch of habitat) for monarch butterflies by planting native milkweeds and other nectar plants in your own garden or yard. Monarchs rely on milkweed plants for reproduction, so these are the most important plants to include in you monarch habitat. Other plants to include as food sources for adult monarchs are goldenrod, zinnias, alyssum, purple coneflower, asters, and bergamot (bee balm).

It is also vitally important that you avoid using pesticides in your garden and on your lawn if you want to protect monarch butterflies. Consider organic, eco-friendly alternatives, such as strategically planting plants that deter pests and using mulch to prevent weed growth.

Though human activity has caused substantial decline in monarch butterfly populations, it isn’t too late. We can still restore their habitats and see this butterfly species flourish once more.

Resources

This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.

© 2021 Jennifer Wilber

Related Articles