Featured Creature: Monarch Butterfly

Photo by Bill Barlow

What iconic creature thinks beyond its lifespan, navigates new terrain with grace, and stuns North America with its migrations?

The monarch butterfly! 

Photo by Bill Barlow

Living life in cycles

The monarch butterfly is famous for its beauty and for its unique patterns of breeding, migrating, and hibernating. There are two main populations of monarch butterflies in North America: Eastern Monarch Butterflies (found east of the Rocky Mountains), and Western Monarch Butterflies (found west of the Rockies across California). They used to be found throughout South America as well, but have sadly disappeared there. Some populations also exist in other areas of the globe like Hawaii and Oceania. 

Like all butterflies, monarchs start out as caterpillar larvae. Adult monarchs only lay their eggs on one plant, milkweed, as it is the only food that monarch caterpillars consume. Milkweed contains toxins that monarch butterflies have developed a tolerance for, so they are unharmed by the substance, and they retain its toxins into their adult lives as protection from predation. As they say, you are what you eat!

Check out this short time-lapse video of the monarch butterfly’s life cycle:

A remarkable foresight, and a differing lifespan

One of the most notable features of monarch butterflies is the migrations that some subspecies undertake. Eastern monarch butterflies collectively carry out a migration of up to 3,000 miles, much greater than other migrating insects.

Monarch butterflies famously carry out these seasonal migrations over multiple generations. Since most adult monarch butterflies live only a few weeks, it takes three generations of monarchs to complete the journey from South to North in the spring. The cycle is completed with one special generation, which migrates during the fall and overwinters in Mexico, having made the full journey from North to South within their lifetimes. This means that unlike migrating birds, all of these monarchs are flying toward places they’ve never been before, and for the transitory generations of spring migrating monarchs, their entire lives take place on the move. 

Astonishingly, the overwintering monarchs and the spring migrating monarchs experience different lifespans and behaviors. The spring migrating monarchs live only a few weeks long and reproduce soon after emerging as mature butterflies. They breed quickly and move Northward to lay eggs on available milkweed.

In contrast, the overwintering monarchs, which stay in the more temperate South through the winter, actually live for several months and complete the fall migration from north to south in one generation. They emerge as adult butterflies in a state called “diapause,” in which their reproductive organs are not yet mature. They consume nectar and prepare for their journey South, and only reproduce after they have finished migrating and weathering the winter season. The biological mechanism for these differences has not been determined, though it’s observed that overwintering monarchs that move from North to South in the fall have small, agile bodies that rely on fat reserves to support their long journeys. 

Both overwintering and transitory generations of monarchs are incredible in different ways. The overwintering generations complete a tremendous journey, navigating for thousands of miles to new landscapes. It is thought that they use an internal magnetic compass to aid in their journey, and make use of favorable winds to help them span the long distances. The transitory generations that only participate in smaller legs of the spring migration northward may not live as long or cover as much ground, but they offer a touching example of legacy and multigenerational work. Though they survive for just a few weeks and never see the final destination they journey toward, their great-great-grandchildren benefit from the travels they took. 

Monarch Butterfly Spring and Summer Migration Patterns. Base map source: USGS National Atlas.
Monarch Butterfly Fall Migration Patterns (Overwintering Monarchs). Base map source: USGS National Atlas.

How are human activities impacting monarchs?

Since monarchs rely on milkweed to provide food for their caterpillar offspring, diminishing sources of milkweed across the wide range of their flightpath undermine monarchs’ ability to reproduce successive generations. 

And although milkweed toxins protect them from a lot of predators, a few animals and insects are still able to digest monarch butterflies, and prey on the creatures when given a chance. Therefore, it’s important that monarchs are able to successfully complete their migrations in enough numbers to keep the chain going. The migrations they undertake are set off by cues in temperature and climate, and erratic weather patterns that are growing more frequent due to climate change can throw them off. 

Deforestation and land use changes from grassland to pasture also disrupt monarchs’ capacity to survive. The Oyamel forests in Mexico where Eastern monarch butterfly populations overwinter have shrunk in past decades under economic pressure to convert to cropland. Across the butterflies’ flight paths, milkweed (along with other native pollinator plants) has been removed from agricultural areas mechanically or chemically, and without this vegetation, monarchs cannot lay eggs and reproduce further generations. The use of herbicides and pesticides as widespread methods of raising crops is a major threat to migrating monarchs.

Monarch butterflies cover a tree at El Rosario Monarch Butterfly Sanctuary in Michoacán, Mexico. (Photo by D. André Green II)

However, there’s a lot we can do to support these beautiful creatures! On a broad scale, we can work to combat climate change and land degradation by supporting efforts to restore ecosystems. We can advocate for farming methods that phase out herbicides and pesticides and support organic and regenerative agriculture – both the policies that support the practice and the farms and organizations that carry it out. In our own communities and gardens, we can plant milkweed and other native wildflowers to bolster not just monarchs, but other migrating butterflies, insects, and birds. You can participate in citizen science efforts to keep track of monarch populations, and find out what kind of milkweed native to your region is good for planting to support monarch butterflies.

We can all keep watching out for and sharing information on our winged friends, and learn from them as we try to make the world a place where they, and all of us, can thrive. Check out a short blog post I wrote on the monarch’s lessons for us on time and continuity. Our relationship is a two way street, and we have much to learn from these bright butterflies.             

By Maya Dutta