Posted On: August 20, 2019
Beckoning the Butterflies
Danaus plexippus, the Monarch butterfly, is perhaps the most iconic butterfly across the Americas. The much beloved butterfly is a common sight in the United States east of the Rocky Mountains with a smaller population living on the west coast, and its native range extends from southern Canada down to South America and the Carribean. The monarch is a migratory butterfly and makes the longest journey of all butterflies, travelling up to 3000 miles to escape winter frosts. The eastern population travels southward down to Mexico and the Carribean for the winter, while the western groups travel to southern California. There, they cover trees in groups of hundreds or thousands to stay warm during the winter. Once spring begins, the monarchs will reproduce and their children journey back northwards. These migrations happen over the course of several generations, with each successive generation travelling closer to their final home. It takes between three and five generations before the monarch will have repopulated North America on its northward migration.
The monarch begins its life as an egg laid on a milkweed, flowers that belong to the genus Asclepias. A female monarch lays her eggs one at a time on the leaves or flowers of a milkweed. After three to five days, the eggs hatch and the larvae, dubbed the first instar but commonly called a caterpillar, emerges. This caterpillar’s first action is to consume the remains of its egg before then moving on to its host plant. As the caterpillar develops, it will molt several times, shedding its skin to become larger and developing more pronounced stripes. The host plants of the monarch, milkweeds, invariably contain chemicals toxic to vertebrates, including most birds and mammals. These toxins build up in the body of the monarch and act as a deterrent against predation, acting in concert with their bright coloration to send a warning to any would-be predators. Once the caterpillar has molted five times, it attaches itself to a stem with a line of silk and molts one final time, this time revealing a hard, shiny exoskeleton dubbed a chrysalis. Contrary to popular belief, only moths spin cocoons made of silk around themselves; butterflies possess hard, often metallic-seeming chrysalides. After developing for about two weeks, the adult butterfly, or imago, emerges from its now transparent chrysalis. All the generations of monarchs with the exception of the final, migratory generation, will live for only a few weeks, eating, mating, and laying the eggs that will restart the cycle.
Monarch butterflies are one of the most well-known insects in the western hemisphere, and their migration is a truly spectacular sight. However, despite their beloved nature, the monarch is under threat from changing climates and reduction in their habitat. The monarch is almost entirely dependent on milkweeds as a caterpillar, spending that entire phase of their life cycle eating and living on those plants. Unfortunately, milkweeds are also considered an agricultural pest in many parts of the United States. The places where most monarchs are born, the Corn Belt, used to be full of milkweeds that provided food for monarchs and places to rest and lay eggs. These days, milkweeds are often removed from agricultural land, and as more land is converted for crop use, less land is left for milkweeds and monarchs. In addition to losing land in their northern range, overwintering sites in Mexico and warmer areas are rapidly becoming less hospitable to the monarch. Studies have documented as much as 90% decreases in total overwintering populations, and 50% declines in western populations. Currently, the monarch is not considered an endangered species. However, their decline is so steep that conservation scientists petitioned, then successfully sued the U.S Fish and Wildlife Service to force a review of their conservation status. The deadline for this review was originally June of 2019, but this has been extended until December of 2020. Here in the park, we have included a generous planting of Asclepias curassavica, tropical milkweed, specifically the cultivars ‘Silky Gold’ and ‘Silky Scarlet’, as part of our garden beds to help support our Monarch butterflies. In the Magnolia bed, these milkweeds are interplanted with knotweed, echinacea, and sneezeweed to attract a variety of pollinators. Milkweeds also feature in the pollinator friendly gardens around the Dog Run, along with more sneezeweed and echinacea, as well as black-eyed Susan and bee-balm. Monarch butterflies have been seen in all stages of their life cycle at Madison Square Park proving that if you build it, nature will come back.