- King Monarch Butterflies Weigh 1/20th as Much as Hummingbirds, but Migrate Just As Far.
- How You Can Help Ensure the Future of the Monarch Butterfly
- Milkweed Plants Are The Essential Key
By Jim Low
“Acts of creation are ordinarily reserved for gods and poets, but humbler folk may circumvent this restriction if they know how. To plant a pine, for example, one need be neither god nor poet; one need only own a good shovel.”
I thought of this quote from Aldo Leopold’s A Sand County Almanac recently, when I received a press release from Missourians for Monarchs, a public/private partnership to conserve North America’s best-known butterfly species.
The release noted that the early arrival of spring-like weather had caused monarch butterflies to begin their northward migration unusually early. It went on to say that the fragile migrants were carrying unusually large numbers of eggs this year. That sounded like great news at first blush, but the release went on to say that naturalists were worried that the advanced timing of migration could cause a reproductive failure. Monarch larvae can only survive on milkweed plants. Butterfly experts feared that milkweeds (Missouri has nine species), might not be growing when monarchs arrived, ready to lay their eggs.
“To support the caterpillars, we’re going to need every stem of milkweed out there,” said Missourians for Monarchs Coordinator Jason Jenkins, “So we’re encouraging landowners to hold off on any springtime mowing to help this first generation of monarchs thrive.”
That’s when I thought of Aldo Leopold’s quote. It just so happens that I have a nice little patch of milkweed growing in my front yard. The press release was well-timed, because I had not mowed the lawn yet, and milkweed plants already were poking their heads up. I went ahead and mowed the lawn, but I detoured around each of the two dozen milkweed plants. I know it looks odd to human visitors, but it’s the orange-and-black, six-legged visitors I’m most concerned about.
The life history of the monarch butterfly, which took decades to unravel, is so complex and improbable, it seems made up. Monarchs make a late-summer and autumn migration to Florida, southern California or Mexico, where they spend the winter. The following spring, they begin a northward migration that takes several years – and multiple generations – to complete. Along the way, they harvest nectar from flowers to sustain themselves. Only their larvae require milkweed for food.
Northward migrating, they mate and lay eggs along their way. The larvae begin feeding on milkweed leaves immediately, chewing in a circular pattern that prevents entrapment in the plant’s sticky sap. The leaves and sap contain cardenolides, toxic substances that the larvae concentrate, making them poisonous to most birds and other potential vertebrate predators.
Those foolish enough to consume a monarch larva or adult don’t survive to pass their genes on to the next generation. Only those that have no interest in eating monarchs survive, vastly reducing the threat to this species. The viceroy butterfly, which is not toxic, has evolved to mimic the monarch’s color pattern, and thus enjoys an indirect Darwinian advantage. Black-backed orioles and black-headed grosbeaks are not susceptible to cardenolide poisoning, and account for more than half the mortality of monarchs that winter in central Mexico.
Monarch larvae pass through five stages, known as instars. The first instar is tiny – 2 to 6 mm long. At this stage, they are a pale translucent green. Like other insects, monarchs must shed their skins to grow, passing into the next instar with each molt. Along the way, they develop a striking white, yellow and black transverse bands, grow long tentacles fore and aft and develop body segments that increasingly resemble their adult form. By the time they complete the fifth instar, they have increased their mass by a factor of 2,000 and are nearly 2 inches long. Then they are ready to pupate.
The monarch’s chrysalis is a work of art not unlike the wrapping of gifts for Chinese emperors. The delicate mint-green exterior is adorned with golden – not yellow, mind you, shimmering gold – spangles. One to two weeks after pupation, the chrysalis becomes clear, and the adult butterfly emerges. It hangs upside down while it pumps body fluids into its furled wings to expand them. The transition from egg to adult takes anywhere from 25 days to seven weeks during the warm months. They are sexually mature less than a week later. Female monarchs are polyandrous and produce more eggs the more partners they have.
Monarchs migrate from their wintering grounds to breeding areas and back in one year, but not in one generation. Generation Number 1 is the one that migrates south in the fall. In January or February, they mate and head back north, reaching Texas or Oklahoma, where they (hopefully) find milkweed plants, lay eggs and die after a long – for monarchs – life of eight or nine months. Generation No. 2 hatches, matures, flies farther north, mates, lays eggs and dies. This repeats another time or two, until the northernmost breeding ground is reached. There, another two or three generations are born. The last one might be Generation Number 5 or 6 of that year, but they are destined to become Generation Number 1 the following year, after migrating south and spending the winter.
In this way, monarchs avoid the hot, dry summers that would make their wintering grounds unlivable, and the cold winters that would make it impossible to survive on their breeding grounds. They also avoid sticking around any one place long enough for predators, diseases and parasites to build up and take advantage of the nutritional resource that monarchs represent.
Getting back to Aldo Leopold, you too, can wield god-like powers, if not of creation, then at least of conservation.
Habitat loss and fragmentation, along with changes in weather have led to a steep decline in monarch numbers over the past 20 years. Butterfly conservation groups say individuals can make a difference. Make room for monarchs on your property, whether it is a quarter-acre residential lot or a 5,000-acre farm.
Spare the milkweed plants that grow naturally by delaying mowing as long as possible or mowing around patches of milkweed. You also can plant native milkweeds, which are available from wildflower nurseries listed at Grow Native! These will reward your efforts with beautiful flowers that are well adapted to Missouri’s climate and require little or no maintenance.
The Missouri Department of Conservation has a monarch habitat web page about creating monarch habitat too, and the U.S. Fish and Wildlife Service has monarch conservation strategies for individual and communities. And take time to look at the Missourians for Monarchs blog, which has fascinating facts and beautiful photos.
You have the power.
Citizen action is what makes conservation work in Missouri and everywhere else too,