Signs of Fall 4 – Milkweed and Monarchs

This past summer has been very wet here in Western Pennsylvania. We have exceeded our to-date summer rainfall by almost five inches. All this extra rain has stimulated our lawns and the plants in our gardens (especially the weeds!) and roadside spaces to grow thickly and lushly. Some of us have even seen plants that we have never seen before because of their incredibly positive responses to the very abundant moisture!

One plant that has really thrived in the wet conditions has been milkweed (Asclepias syriaca). This tall, perennial plant is growing wildly around our house. In spots where one or two milkweed plants have historically grown we have had six or seven growing this summer. Each of them flowered, too, and has produced large seed pods that are ripening and getting ready to release huge numbers of their white, fluffy, floating seeds.

I welcome the milkweed around our house and always lobby to let them grow and go to seed. I hope each year to see monarch butterfly (Danaus plexippus) caterpillars on the plants chewing their ways through the thick leaves absorbing the milkweed’s toxins (cardiac glycosides) into their tissues to give them protection from potential predators.  I have yet to find, though, any monarch caterpillars around our house even after 15 years of looking!   

Tracie Brockhoff reports that their hay fields up in central Armstrong County have great patches of milkweed growing in them this year. This is the first time she has seen such prominent milkweed out in these fields. Milkweed’s ability to spread via rhizomes in the moist field soil has probably generated these large, dense, hay field patches.  Milkweed is classified by the University of Kentucky COOP Extension as an “occasional risk” poison to livestock in both its green and in its dried (hay) form. These plants, then, need to be removed from the fields before the last cutting of hay can proceed.

Milkweed according to the USDA National Resource Conservation Service is readily propagated from seed. They describe spreading new milkweed seeds on cleared soil patches or in planting pots and realizing a high percentage of viable plants. That has not been my experience with milkweed, though. Out on the Butterfly and Pollinator plots near the entrance to the Campus Nature Trail I have spread hundreds of milkweed seeds over the years and have gotten none of them to germinate. Maybe the USDA is a bit too optimistic in its description of milkweed propagation, or maybe it is just another example of my brown thumbs.

We are starting to see the first monarch butterflies fluttering along on their inevitable flights to the west and south. These individuals are links in one of the truly great migrations of nature. This current generation of adults (which may be the fourth generation of the season) moves steadily south and west until they reach their overwintering sites in the pine and oak forests of the mountains of the Mexican States of Michoacan and Mexico. These overwintering monarchs wait out the cold of the winter in groups that seem to smother the trees of these forests and then begin their flights back north in February and March. They reproduce on the way and their progeny continue on the step by step trip back to Western Pennsylvania and other parts of northern North America. The milkweed is, according to some authorities, the ONLY plant that these monarch caterpillars will feed on, and the wave of butterflies coming north in the spring follows the spring and summer emergence of these plants. I have seen monarch caterpillars feeding on other plant species but acknowledge that their presence on these plants may have been very unusual occurrences. The milkweed, without a doubt, with its load of protective toxins, is extremely important for this beautiful butterfly species.
 
Yesterday, we cut most of the milkweed stems around our house (the storms this week had battered the plants and knocked them to the ground). We are watching for the passing monarchs, though, maybe even the ones that have fed on the plants up in Tracie’s hay fields!