Common Milkweed: A Frequent Stop

From May until October, Common milkweed is one of the flowers that I stop at regularly on my rounds in Eliza Howell Park. From being a “weed” in need of eradication, it has in recent years acquired both respectability and fame as a host plant for the larvae of the popular Monarch butterfly. I watch it for that role and for many other reasons.

In September, the plants, many of them 4 feet tall, are dominated by follicles (seed pods).

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When the seed pods open – and some are just beginning to do so – we can witness the delicate beauty of the seeds attached to the silk that allows them to be dispersed by the wind. This is definitely worth seeking out a sunny fall day.

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Common Milkweed is a perennial wildflower native to eastern North America that spreads both by seeds and by underground rhizomes, the second being the reason they are often found in patches. They sprout in May, usually shortly before the Monarchs return. (This year I saw the first Monarch on May 15.)

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Monarchs start laying eggs on the milkweed leaves almost immediately after arrival. Once hatched, the larvae (caterpillars) eat the tender leaves. This picture of a tiny caterpillar is from early June.

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By the end of June, milkweed is beginning to flower. I was especially struck this year by how fragrant the flowers are. Even for someone like me, who does not have the most sensitive nose, it is easy to know that one is in a patch of blooming milkweeds from the fragrance alone.

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Milkweeds get their name from the fact that leaves and stems, when broken, produce a milky sap. There is a toxicity in the milkweed plant and Monarchs acquire this toxicity from ingesting the leaves as caterpillars. The result is that adult Monarchs are not preyed upon by birds, who have come to know that Monarchs are not healthy food.

Monarch butterflies are not the only insect that benefits from using Common Milkweed as a host plant for young. In September, it is easy to find seed pods covered with Large Milkweed Bugs. In the picture, the left shows adult Large Milkweed Bugs and the right picture is of young ones (nymphs). (Yes, there are Small Milkweed Bugs, but not in this entry.)

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Large Milkweed Bugs have some characteristics similar to Monarchs: milkweed is the host plant on which the young feed; they are orange and black; they acquire a protective toxicity from milkweed; they migrate south for the winter.

I have recognized Common Milkweed for as long as I can remember, but I have only really gotten to know it from my observations in Eliza Howell Park in recent years. The more I know about it, the more I like it.

 

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Monarchs and the Milkweed Advantage

Monarch butterflies are again active in Eliza Howell Park. Monarchs are among the most visible and common of the roughly two dozen butterfly species found in the park and one of the few butterfly species that migrate (they head to Mexico each Fall). They have returned. To be exact, it is not the same individuals that have returned (their lifespan is not that long). But Monarchs are back.

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Photo by Margaret Weber

At the same time that I started seeing the first Monarchs of the year I began to notice that Common Milkweed, the wildflower that their life history is intimately connected with, have emerged and are growing rapidly.

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Monarchs use milkweeds (mostly the Common Milkweed) as the exclusive host plant for their eggs and larvae. They will soon be beginning the process. Nature walkers will be checking the underside of milkweed leaves for the Monarch caterpillar, almost as easily identified as the adult butterfly.

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Photo by Margaret Weber

Monarchs nectar on many different flowers (in the first picture above, it is on a butterfly bush), but its special relationship with milkweed in reproduction gives it what I think of as the “milkweed advantage.” There is a toxicity in all parts of the milkweed plant (ranchers/farmers are warned again letting their livestock graze it) and the Monarch acquires this toxicity from ingesting the leaves as caterpillars. The result is that adult Monarchs are not preyed upon by birds, who have come to know that Monarchs are not healthy food.

It is not a surprise that Monarchs like milkweed.

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Photo by Margaret Weber

The Monarch is one of the best known and best liked butterflies in this part of the country and there has been a growing concern in recent years about the decline in their numbers. They continue in good numbers in Eliza Howell Park, perhaps in part due to the limited mowing that allows milkweeds to thrive. 

The milkweed flower is followed by the seed pods, which will ripen and open to silky seeds that are dispersed by wind. 

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When I saw the first Monarchs last week, I immediately looked for milkweed. The two go together that closely. 

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Postscript: There is another insect that benefits from the toxic “milkweed advantage.” It is the brightly colored Milkweed Bug, found on the plants later in the year. That may be a story for another time. 

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