Help Save the Monarch Butterfly!

by Jan Thornhill

What’s not to like about monarchs? Their caterpillars are gorgeously striped. Their chrysalises are an otherworldly green bejeweled with glimmering gold. The adults weigh only half as much as a paperclip, yet can migrate thousands of kilometres—and if you’re lucky enough to be in the right place at the right time you can see congregations of thousands. Monarchs can also make blue jays throw up—a delightful tidbit I learned while researching my new book about migration, Is This Panama? (beautifully illustrated by Soyeon Kim!). Sadly, just as the book went to press, bad news arrived: the over-wintering monarch population in Mexico was the lowest ever recorded.

Roosting monarchs (Agunther)

Hundreds of millions of monarchs migrate each fall to warmer areas. Adults that originate in southern Canada can fly more than 4,000 kilometres (2,500 miles) to reach their hibernation grounds in Mexico. It’s a treacherous journey for a delicate butterfly and many die on the way, but every year millions arrive in a mountain forest near Mexico City. Because it would be too difficult to actually count such large numbers, scientists have been measuring the area of forest each year that the butterflies occupy. In 2011 monarchs covered the trees in 2.89 hectares of forest. This past winter they occupied only 1.19 hectares (5 sq. miles)—a drop of 59%!

Though adult monarchs sip nectar from a variety of flowers, their caterpillars are specialist herbivores, which means they depend on a single type of plant for food. In the monarch’s case, these plants all belong to the milkweed family.

Between hatching and forming a chrysalis, monarch caterpillars increase 3,000 times in size. These two caterpillars are in their second and third stages of growth, called instars. (Jan Thornhill)

Milkweeds have evolved elaborate defenses to prevent themselves from being eaten, including uncomfortably hairy leaves, sticky white latex that bleeds from injured tissues, and toxins called cardenolides. Because of the cardenolides, most insects, as well as vertebrates, avoid eating milkweed, but the monarch has evolved to not only tolerate the toxins, it also uses those very poisons to its own advantage by storing them in its own body, which makes even an adult butterfly just as toxic as the plant. The first time a bird, such as a blue jay, eats a monarch, it will vomit a short time later. Though this is of no benefit to the monarch that was eaten, the bird will remember its bad experience and will avoid eating black-and-orange butterflies from then on.

Meanwhile, milkweed plants are continuing to evolve in response to being eaten by caterpillars. Recent genetic research is showing that there is an evolutionary trend in milkweeds towards healing themselves faster than they can be eaten, instead of producing more toxins that might eventually deter caterpillars. 

Monarch caterpillar on milkweed flowers (Jan Thornhill)

Though milkweeds can get along perfectly well without monarchs, monarchs cannot survive without milkweeds. Unfortunately, milkweeds of all varieties are disappearing. Their grassland habitats have been steadily eroding for more than a century due to human development, and recent severe droughts in Texas and the American Southwest have also taken their toll. But another much greater threat has arrived: farmers across North America are now growing corn and soybeans that are genetically engineered to be herbicide resistant. When these “Roundup Ready” crops, developed by a company called Monsanto, are sprayed with glyphosate-based herbicide, almost any plant—other than the corn and soybeans—is killed. The plants that once grew alongside these crops include milkweed, which, until now, had always been plentiful, as well as a multitude of wildflowers that provide nectar for adult butterflies while they’re migrating. One study has shown that between 1999 and 2009 there has been a 90% loss of common milkweeds in the fields treated with these herbicides.* Soon there may be no milkweed in these croplands at all. And no monarchs.

So What Can We Do To Help?

Grow milkweed in your backyard or in your schoolyard:

http://monarchwatch.org/bring-back-the-monarchs/resources/plant-seed-suppliers

http://www.livemonarch.com/free-milkweed-seeds.htm

Grow a “butterfly garden” with plants that provide food for caterpillars and/or nectar for butterflies:

http://www2.ville.montreal.qc.ca/jardin/en/info_verte/papillons/papillons.htm

 Learn more about monarchs and share what you learn: http://www.monarchwatch.org

Help monarch researchers: http://www.monarchwatch.org/class/studproj/index.htm

 

Lobby your political representatives to have products made with genetically modified (GM) crops labeled.

*Pleasants, J.M and Oberhauser, K.S.. 2012. Milkweed loss in agricultural fields due to herbicide use: Effect on the Monarch Butterfly population. Insect Conservation and Diversity (March 12, doi: 10.1111/j.1752-4598.2012.00196x)