Common milkweed isn’t a particularly finicky plant—it has “weed” in its name for a reason and can be found growing on roadsides, empty lots, and old fields. But over the last two decades, Asclepias syriaca, which is primarily found in the Midwest and eastern United States, has disappeared from most agricultural landscapes. Along with it, the population of the iconic migratory monarch butterfly, Danaus plexippus plexippus, which relies on the plant for reproduction, has also crashed, so much so that it is being considered for endangered status.
According to researchers, 1.3 billion stems of milkweed have disappeared from Midwestern farmlands over the last 20 years. This has led to an 80 percent crash in the migratory monarch, which winters in the mountains of Mexico and breeds in the central and eastern United States during the spring and summer. Since hitting an estimated high of 682 million monarchs in 1997, the species dropped to just 42 million in 2015. According to another study, milkweed in and near cropland in Illinois, prime monarch habitat, has dropped by 95 percent over the same period—representing a 50 percent drop in the total milkweed population.