No one is completely immune to the effects of a changing climate, but some species are more highly affected than others. Perhaps you’ve heard that the populations of monarch butterflies are declining and you want to know more. How is the monarch butterfly affected by climate change? What other factors have contributed to its declining numbers? Keep reading as we explore these important questions.
What You'll Learn Today
What is the Monarch Butterfly?
Monarchs are beautiful orange butterflies with black bodies and black stripes on their wings. They are one of the most highly recognizable butterflies in North America.
These butterflies are well-known for their yearly migration from Canada to Mexico. They make this journey each fall to escape the cold winters farther north; in the spring, they return part of the way before mating, laying eggs, and dying, then the next generation of monarchs completes the return home.
Because of this migration, monarchs can be found throughout North America at different times of the year. They have been seen in the northern parts of Canada during the summer, and they are widely distributed throughout the United States for much of the year.
Monarch butterflies mate and lay eggs throughout the summer, generally producing about three generations per year. Each female lays hundreds of eggs during its lifespan.
Spring and summer monarchs live about two to six weeks as adult butterflies. The fall monarchs live for several months as they make their long journey southward and spend the winter in the forests of Mexico.
Check out this video for some impressive footage of a swarm of overwintering monarchs:
How Does Climate Change Affect Monarch Butterflies?
Changes in long-term climate patterns have greatly affected monarch butterflies. In fact, overall monarch populations in North America have declined by about 95 percent in recent decades.
While climate change is not the only factor in this decline, it has played a large role.
Monarchs depend on clues such as temperature to tell them when to begin their migration and when to start moving again every step along the way. Each year, the migration begins later and later as warm weather conditions linger far into Canada.
Once the weather finally begins to cool, it often turns cold very quickly. Monarchs that migrate later in the fall face a greater risk of death as temperatures drop near or below freezing.
Once they are in Mexico, they may begin migrating too early or too late depending on the weather and climate patterns they experience. An unseasonably cold winter may kill many of the hibernating monarchs; an unseasonably warm winter may cause them to leave too early, running into deadly cold as they travel north.
Temperature extremes such as these are becoming more common as our climate changes. Temperature extremes lead to other weather-related extremes, such as severe storms and periods of deadly drought.
These other extremes can also impact monarch survival. One massive storm hit the butterflies’ overwintering grounds in 2002, wiping out about 80 percent of the entire monarch population with a single stroke.
What Other Threats Do Monarch Butterflies Face?
As mentioned above, climate change has a major effect on monarchs; but it is not the only threat to their survival. Some other threats monarchs face include:
- Loss of habitat: Monarchs depend on milkweed for survival, but milkweed is often treated as an invasive species and eradicated from fields and farmland. With less milkweed for monarch caterpillars to eat, fewer and fewer caterpillars are surviving to adulthood.
What’s more, illegal logging has been a problem in Mexico where the monarchs spend the winter. According to an article by Discovery, “the Monarch Biosphere Reserve in Michoacán, Mexico, lost trees at a higher rate [in 2020] than it did in 2019.” When these trees are removed, the monarchs have fewer places to roost during periods of hibernation, leaving them vulnerable.
- Pesticides: Pesticides are commonly used throughout the Corn Belt region of the U.S., which makes up a large portion of monarchs’ migration route. Not only do these pesticides greatly decimate local populations of monarchs, but they can also kill the monarchs just passing through on their migration.
- Breeding struggles: A combination of the above factors have made breeding more difficult for monarchs. Loss of habitat makes it challenging for female monarchs to find places to lay their eggs; pesticides kill both caterpillars and adult butterflies; and climate change negatively impacts their overall reproductive ability.
What Can We Do?
Habitat restoration is one of the most important things we can do to save the monarchs. While large-scale, global changes will be needed to impact climate change, those who are interested in doing their part can plant native milkweed species in their yards to attract monarchs and give them a safe place to reproduce.
It’s also important to refrain from using pesticides and insecticides in your yard. These products are unsafe to humans and can kill monarch caterpillars and butterflies, as well as destroy the plants they depend on for survival.
Monarch butterflies have been greatly affected by climate change and various other factors in the past few decades. To help preserve and restore their numbers, you can plant milkweed and refrain from using pesticides and insecticides, as well as participate in larger efforts to protect these butterflies.