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Milkweed and Monarchs, and Philly butterfly habitat

Monarch butterfly (Danaus plexippus) on Milkweed (genus Asclepias), with White Clover (Trifolium repens) in the background.

Even though most people can’t identify any butterflies, I’d be willing to bet that of those who can identify a butterfly, most of them can identify a Monarch. It’s orange and black, it’s large, it flies slowly and out in the open, and it often occurs in large numbers. Monarchs live in places as distant as the west coast of North America, the Caribbean, Spain, northern south America, and the South Pacific including eastern Australia and Papua New Guinea.

Monarchs pass through our area as part of an incredible years- and generations-long journey. One generation of this population, in the fall, travels from northern North America south to wintering grounds in Mexico, Northern Florida, and other subtropical locations. There they spend the winter, and then in the spring travel north over many months. During this period, however, the average Monarch only lives around sixteen weeks, and so up to four generations come and go on the slow trip north. This means that the butterflies that return to our area are the great-grandchildren of those that left.

While adult Monarch can live off of the nectar of a variety of plants, this species is much more limited in its choice of host for laying eggs and nurturing caterpillars. For reproduction, Monarchs rely primarily on Milkweeds. They need Milkweeds to successfully reproduce and thus continue their migratory cycle.

There are many different species of Milkweed that occur in our area and can host the insect. But there’s a problem: As human numbers increased over the last few hundred years and we’ve invented industrialized food production, we often have come to adopt agricultural practices that rely on mono-cropping. This means that when we grow food, we often devote large pieces of land to growing just one type of plant. This in turn reduces the biodiversity of every type of thing that relies on plants. For example, if all that’s growing is corn, or soybeans, there aren’t going to be Milkweeds. Any that persist are eliminated by herbicides. And then, Monarchs don’t have any place to lay eggs or food to eat when they are caterpillars.

Cities like Philadelphia, however, can offer refuge. Because we aren't a mono-culture, because we aren’t consumed with lawns like the suburbs, cities provide a lot of spaces we can fit Milkweed. In fact, the picture at the top of this post was taken in Philadelphia. At a site where I saw approximately 15 Monarch butterflies in 10 minutes on Oct 7th, 2020. The location? A nondescript bit of green in the middle of the 40th street trolley station, right where the tunnel ends and the 11, 13, 34, and 36 trolleys come to the surface. Spots like this give us a great opportunity to provide crucial habitat for Monarch butterflies to raise young, and with our help thier great journey can continue many years and many more generations of butterflies into the future.

40th street trolley stop. The green area in front is where the above pictures were taken.

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