Royal Rovers: The Marvelous Migration of Monarch Butterflies

Imagine making a tedious journey across 3000 miles over two months without accounting for extreme weather or other factors that might delay you. Now imagine that you weigh less than a quarter of an ounce and are only 3-4″ in size. Seems a little tough, doesn’t it? The farthest I have ran is 6.2 miles in a 10K segment of a marathon and it drained all my energy for a week. Now, I’m no Olympian by any stretch, but I have got considerably more going for me than Danaus plexippus, the Monarch butterfly. I am a larger, less fragile organism aided by a wider diet and intellect, among other things, and I can contently set up shack in the same shelter over the course of the next 80 years with relative comfort. I do not have to worry about predators. Heart disease and motor vehicles offer a greater threat to me than do the likes of birds or other insects, not to mention storms or shifting weather patterns. In spite of everything against them, monarchs in North America make an incredible migration from the northern reaches of the United States and Canada down into the heart of Mexico every fall. They do this to better survive the harsh cold of winter to give rise to the next generation, however, their biggest threat today is not the cold, but the continuing impact of human alterations to their environment.

Monarch butterflies are as delicate as they are beautiful, but they do not need to fear much from predators thanks to a steady diet of exclusive milkweed as caterpillars. Milkweed contains toxins that are poisonous or at least downright distasteful to many mammals and birds, and adult monarchs have bright orange and black wings to stand out to warn potential predators of this. This does not take them off the menu for every animal, especially other insects who don’t mind the milkweed, but it keeps them safe from a high number of hungry creatures. Their warning colors are so effective, that Viceroy butterflies copy it to trick predators into thinking that they are poisonous like monarchs. Imitation is the sincerest form of flattery after all.

Monarchs are champion migrants also. As I previously stated, some travel as far as 3000 miles (4828km) to their wintering grounds. This is amazing enough for such a small creature, but especially so when you consider all the work that goes into making a complete cyclical migration to Mexico and back. You probably were introduced to the annual monarch migration early on in your academic career, perhaps even as the first real-world example of animal migration, but did you know that it takes 5-6 generations to make the round trip? It does! The first round of monarchs born in Mexico gradually work their way north, some to the western US, some to the East, and some farther on into Canada. Over the course of the spring and summer 4-5 generations live, migrate, reproduce, and die as they steadily ease on up the States and the land of the Maple Leaf until the final generation is born at the end of summer. This last generation of the year – the one that currently is heading south – is bigger and stronger than their parents, grandparents, great-grandparents, etc. They can be as much as twice as large, all the better to help them make the long trip to Mexico. This final generation is the one that makes the big flight you learned about in grade school. They arrive in Mexico, chill out (literally), and produce the first generation of next year’s journey. Most generations only survive for about 2-6 weeks, but the final, far-flying migrant generation lives for 6-8 months, spending most of it enduring the winter weather.

Yes, even in Mexico it gets chilly. The BBC had a nice segment explaining the overwintering of monarchs in their 2009 nature documentary series Life.

Sorry for the crummy video quality, and more so for the lack of original David Attenborough narration (I guess Oprah’s all right). As she said, predators not deterred by the bad taste and natural occurrences like frost can kill thousands of these butterflies as they wait out the winter, but ultimately their sheer numbers of approximately 300,000 significantly outweigh these natural losses. Nevertheless, that number was once over 1 billion butterflies, and not that long ago either. In the last 20 years, the population of monarchs has dropped almost 90%. This monumental loss in total population does not bode well for such a tiny animal susceptible to even the slightest change. As with any other living thing on Earth, monarchs are detrimentally affected by global climate change and habitat loss (particularly in their Mexican winter sites), both of which have wreaked havoc on the species. The greatest direct threat to monarchs though is the systemic indirect decimation of milkweed.

Monarch larvae (caterpillars) eat only milkweed, not the more variable sugary nectar they consume as adults, so if milkweed decreases, so too do the monarchs. Milkweed is not a plant we harvest as a crop, nor is it as heavily desired as a showy gardening plant as traditional European garden flowers (although interest for the sake of butterflies is growing), so we don’t really give much notice to it when we consider our own eating or aesthetic desires. This is especially the case when we manage our food needs on a mass scale. In order to most effectively protect our desired crops, such as corn and beans, we spray herbicides that kill off those other plants we aren’t going to send to the table. Today this is easily achieved with genetic modifications to the crop plants that protects them against the harmful effects of the herbicide. The plants we want grow healthier than ever while everything else is eliminated. I am not trying to sway you against genetically modified organisms (GMOs), in fact I think they have the potential to help us manage and produce all of our plant-based food needs. Nonetheless, GMOs are a major source of controversy that should be thoroughly discussed with more than our stomachs in mind. One large consideration to be made is in the case of native plants necessary to native wildlife. Milkweed for monarchs is a prime example of this.

Fortunately, there are many people working to remedy the plight of monarch butterflies, and most of them are not sporting Ph.D.s… well, not yet at least. Monarch Watch is the primary source of data collection and research on monarchs. Based out of Kansas University, located in the central flyway of many migrating monarchs, Monarch Watch is one of the largest citizen science programs in North America, meaning that it relies on data collected by people of all ages and trades. Oftentimes it is used as an active teaching experience for students in middle school and up. Monarch Watch provides tags and data sheets that allow those helping to fill out information regarding the release location, date, gender (males have two black pouches on the hind wing that females lack), and whether the specimen(s) released were a wild-caught or captive-raised stock. The tags are stickers placed on the wing that do not inhibit the flight of the butterflies, but make it easy for anyone involved in Monarch Watch to take a look at and report where a specific butterfly is at at any given time. This information is used to track the general course of migration each year and can be used to gauge population health, among other things. ideally, someday sooner than later we can decrease the number of detrimental effects we have on monarchs while simultaneously increasing the number of people involved in citizen science programs like Monarch Watch to better understand the mysterious Monarch.

Thanks for reading! If you are interested in Monarch Watch, check out their website, as well as these sites with some general information that helped me write this post:

Xerces Society

USDA Forest Service

National Geographic

Contact me with any questions, comments, butterfly love, etc. at monotrememadness@gmail.com, and be sure to come back for more fun next week.

Flutter flutter,

Alex

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