Saturday, July 25, 2009

The Marvel of Milkweed

One of my favorite plants is one that is often overlooked by people, possibly because it frequents roadsides and waste areas and is therefore considered a weed. But this “weed” is responsible for the survival of one of our most beloved insects, helped save the lives of many World War II sailors and airmen, and has a sneaky reproductive life. I give you The Milkweed.

Milkweeds are members of the dogbane family and come in 140 varieties, of which I am familiar with about four: the dusty pink common milkweed (Asclepias syriaca), the muted magenta swamp milkweed (Asclepias incarnata), the brilliantly orange butterflyweed (Asclepias tuberosa), and the creamy yellow whorled milkweed (Asclepias verticillata). I suspect the latter is only in gardens, however.

Most of us are familiar with the common milkweed, with its subtlely-colored flowers that bloom in July and August, and its fluffy white parachutes that lift its seeds into the air in the fall. As the name suggests, common milkweed is common, growing stolidly in fields, along roadsides, and even creeping into gardens and yards. Its pale green, oblong leaves are easily recognized, but it’s the cloyingly sweet perfume the flowers emit that usually grabs my attention; it’s almost enough to drive me from the garden!

Ask any child about milkweed and you will probably be informed that it is the food of monarch butterflies. Monarchs, those majestic orange and black butterflies that flit about our gardens in the heat of summer, may feed on a variety of nectaring flowers as adults, but as larvae they are entirely dependent on milkweeds for food. The female seeks out these life-giving plants and lays her tiny golden eggs on the underside of the leaves. Soon they hatch and the teeny little caterpillars begin to feed. As the larvae grow, they shed their skins, becoming larger and larger. Eventually they crawl off to sheltered spots and form their chrysalises, in which they go through “the change,” emerging in less than two weeks as full-fledged adults.

This is fairly common knowledge. But did you also know that milkweed played a vital role in World War II? At one point scientists in both the US and Russia tried to make rubber from the latex compounds in milkweed sap. Unfortunately it wasn’t successful on a commercial basis, but the story didn’t end there.

When the Japanese successfully took over Java and the Philippines, they cut off the US’s supply of kapok, the fluffy fiber of the silk-cotton tree. This fiber was used to provide flotation in life preservers. Without a kapok supply, the US had to find a substitute. Researchers discovered that the hollow, wax-covered fibers of milkweed fluff (technically called floss) were buoyant, waterproof, and six times lighter than wool. The only problem was that it would take up to three years to produce a commercial crop.

The great thing about WWII was the spirit of volunteerism and the “we’re all in this together” philosophy. Civic groups, church groups, school children, farmers – people across Canada and 29 states east of the Rockies set out to collect milkweed pods. Empty onion sacks were ideal for gathering pods, and the government paid fifteen cents a bag; collectors would get an additional five cents if the pods were dried. There was even a slogan to spur on the collectors: “two bags save one life.” It only took a pound and a half of milkweed floss to provide ten hours of flotation to a 150 pound man; this was about the weight of floss collected in two onion bags of pods. Between 1944 and 1945 it was estimated that over 20 million pounds of milkweed pods were collected, enough to fill 700 freight train cars! When processed, it produced over two million pounds of floss, all destined to fill life vests and to line flight suits.

While all of this is pretty fascinating, I find myself amazed by the blossom itself. First off, the flower is truly lovely; I never tire of photographing it. But the flower hides a sneaky, and potentially deadly, secret. Unlike most flowers, its pollen is gathered into sacs called pollinia (as opposed to producing individual grains of pollen). In order to facilitate its reproduction, the flower has five slits formed by adjacent anthers. When an insect lands for a drink of nectar, its foot (or mouth part) slips into one of the slits and gets stuck. If the insect is lucky, it will be able to yank itself free, taking with it a couple pollinia, which have mechanically attached themselves to the insect’s foot (or mouthpart). When the insect flies off to the next flower, it gets snagged again, only this time it deposits the pollinia. Voila! Reproduction accomplished. And how is this potentially deadly? Because sometimes the hapless bumblebee cannot get her foot unstuck and she dies in the clutch of the milkweed flower. I’ve seen it happen.

For those who like to forage for food or wild medicinals, milkweed has many an admirer, both historically and today. I’ve eaten the buds sautéed in butter, and the small immature pods pickled. Something to keep in mind, though, is the chemical make up of the milkweed’s sap. This sticky white juice is loaded with alkaloids, latex and other compounds, including cardenoilids, which are a type of steroid. So far that doesn’t seem to be too off-putting, but these steroids are what the monarch larva stores in its body to ward off predators: they are toxic and can cause cardiac arrest. This is why many of the insects that feed on milkweeds are brightly colored (red and black, or orange and black). Most predators (namely birds) take this warning seriously and avoid the potentially lethal snack. Two birds, however, are immune to the effects of the toxins: black-headed grosbeaks and black-backed orioles. These birds are known to wreak havoc on over-wintering populations of monarch butterflies.

The next time you pass your friendly neighborhood patch of milkweed, take a moment to check out this heroic plant. Perhaps you can send a silent thanks to its ancestors for helping keep your ancestors alive. Or maybe you’ll be able to watch a busy bee assist in pollination. Or, if it is fall, you can take up one of my all-time favorite activities and spread the wealth of milkweeds my setting the parachutes free from their pods.

 


Ellen Rathbone

Ellen Rathbone is by her own admission a “certified nature nut.” She began contributing to the Adirondack Almanack while living in Newcomb, when she was an environmental educator for the Adirondack Park Agency’s Visitor Interpretive Centers for nearly ten years.

Ellen graduated from SUNY ESF in 1988 with a BS in forestry and biology and has worked as a naturalist in New York, New Jersey, and Vermont.

In 2010 her work took her to Michigan, where she currently resides and serves as Education Director of the Dahlem Conservancy just outside Jackson, Michigan.

She also writes her own blog about her Michigan adventures.





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