The marvel of monarch migration

Monarch butterflies do not wear sunglasses, and yet…

Buckle your seatbelt. You’re about to take flight on one of Earth’s most incredible animal migratory journeys — riding along with the monarch butterfly. Let’s begin in Canada and the Northern U.S., starting somewhere in the August to October time frame.

The monarchs have noticed that it is getting quite chilly, so they pack their sunglasses and swimsuits and embark on a winter vacation to Mexico or California. (I’m jealous). 

As luxurious as it might sound, their journey is not one of choice but of necessity. Monarch butterflies cannot survive the cold winters up north. Thus, eastern monarchs – those residing east of the Rockies – migrate to the Sierra Madre Mountains of Mexico, and their western relatives head to the warmer coastal areas of California.

Extraordinary navigation skills 

That’s a long way to go for such a small creature. These butterflies can travel up to 3,000 miles to reach their final destination. What’s even more astonishing is their ability to figure out where to go, and no, it’s not by using Google maps. Monarchs use the sun. But given that these butterflies are looking for very specific sites to migrate to and the sun isn’t stationary, they need a way to effectively read it.

Luckily for monarchs, their antennas act as an internal clock. This clock will send neurons to the brain, telling the monarch what time of day it is. For example, if a monarch receives information that it is mid morning, it will know to fly with the sun on its left. Late afternoon? The sun should be on its right. This embedded navigation system allows the butterfly to successfully get where it needs to go. 

Special cells in their eyes can even help them find the sun when it’s cloudy outside by using polarized light. Meanwhile, I can barely read a whiteboard from the back of the classroom!

Several generations are needed for the trip

Fast forward — they’ve made it! Taking up to two months, monarchs made the trek down south and ended up at their final destination in order to hibernate throughout the winter months.

After hibernation, these butterflies decide they’ve had enough relaxation, and it is time to venture back toward their summer home. But for these butterflies, their time on this earth is running out. With a lifespan of up to 9 months, their role is to start this long journey home and then pass the baton to their offspring. 

Step one: eastern monarchs fly north into the United States and find some nice looking milkweed plants on which to lay their eggs. This is done purposefully, as their larva offspring rely exclusively on milkweed to survive.

As this next generation is born, their explorer parents come to an eternal rest. Their job is done, and they have set up their offspring to continue the journey. This new generation of flyers, however, isn’t as lucky as their predecessors. Their lifespan amounts to a mere 6-8 weeks, so they head as far north as they can until they repeat the process of reproduction on milkweed. 

Right now you’re probably thinking, “Wait, didn’t you say a monarch’s lifespan is up to 9 months? Were you lying to me?” Don’t fret, lying isn’t in my moral code. What I haven’t mentioned is that these south-bound butterflies are special. Super, in fact. Called the “super generation,” these butterflies live about 8 times longer than other monarchs.

Temperature, day length, and other factors at play when these monarchs are born provide them with less of one certain type of hormone, the juvenile hormone, which essentially prevents them from aging. Therefore, the quicker-aging non-super monarchs have to fly as far north as they can, reproduce, and allow their offspring to continue the journey as they die. This cycle can occur up to five times before the butterflies reach their northern home, where a new generation of super monarchs is born, resting until they get bit by the inevitable travel bug and head back to their getaways down south. 

The loss of milkweed

What could possibly get in the way of such a spectacular, odds-defying migration? Unfortunately, quite a lot. Habitat loss, pesticide use and disease are just a few examples of why monarch butterfly populations have undergone a horrific decline. Plant-killing herbicides have proven very effective at killing milkweed, and some areas once filled with prairies are now bustling cities. Without milkweed, monarchs can’t stop to reproduce and their migration cycle is torn and ended.

Western monarch populations have dropped by over 90%. In the 1980s, western monarch populations were estimated at about 1 to 4 million. In 2020, only 1,914 monarch butterflies were counted wintering on the California coast.

Eastern monarchs aren’t faring much better, as their population has decreased by 80%. Recent grant programs and population rebound data provide a glimmer of hope, as sightings have increased since 2020, but we are still a long way away from restoring the health of the species. 

Essentially, the main issues at play are the stops along the way. Northbound monarchs need spaces with healthy and abundant milkweed if they have any shot at completing their migration, and even the super generation needs places for resting and nourishment. 

Wildlife Corridors 

The need for accessible and non-threatening migration corridors isn’t exclusive to butterflies. Animals across the country are finding their migration routes obstructed by human development, and we need to act. Bills such as the Wildlife Movement Through Partnerships Act help ensure that all animals have a sufficient path to get where they need to. 

How to Help

If we don’t act, these beautiful orange-and-black flyers may disappear. Fortunately, there are ways to help:

1. Monarch butterflies are not currently covered under the endangered species act. We need to urge Secretary Haaland to include monarchs in this act, which has a 99% success rate of saving species. 
2. Farms used to be places where milkweed could grow near the crops, and thus butterflies could reproduce and feed during their great migration. Today, with all the pesticides in our agricultural system, healthy milkweed is harder to find. That’s why we need to make America’s farms safer for monarchs. 
3. Create your own monarch migration pit stop! Although many crucial reproduction and nurturing sites have been destroyed, you can help restore them, partially. Creating a butterfly garden that includes native milkweed can be an invaluable aid to these butterflies. Plus, if all goes as planned, you’ll get to see beautiful orange and black monarchs in your garden. It’s a win-win!

The monarch butterfly’s one-of-a-kind migration story is one that all people should be able to witness, generation after generation. Let’s do our part to save the monarch butterfly.