Many of us remember first learning about black and orange monarch butterflies in elementary school. Whenever we saw one, it was exciting but not rare. Today that has changed. There are about 80% fewer eastern monarchs now than 40 years ago. Beyond the Rocky Mountains, western monarchs have decreased even more.
In December, the Fish and Wildlife Service declined to put monarch butterflies on the endangered species list although the monarch was an acknowledged candidate. Placement on the list means that the government must finance and oversee a recovery plan. With several other animals in more dire need of the government’s resources, the Fish and Wildlife Service will watch during the next four years to reconsider listing the monarch.
One of the remarkable features of the eastern monarch is its 3,000-mile migration to central Mexico. How can this happen when an adult butterfly typically lives only a few weeks? The northbound journey involves several generations of monarchs while the southbound journey happens with a single generation.
In the spring the first adult monarchs begin flying north. Along the way, they mate, lay eggs and die. Those eggs hatch, the caterpillars pupate, and they emerge as the next generation to continue the journey. Three to five generations complete this relay to areas as far north as southern Canada.
Near the end of the summer, a new generation emerges for the migration back to Mexico. Sexual maturity is delayed in this generation, and the life expectancy is measured in months, not weeks, for the long flight to the winter breeding grounds. No individual butterfly has been over the route before, but each one feels compelled to fly in the right direction.
Another distinction of monarchs is that their caterpillars eat only one genus of plant, Asclepias, commonly known as milkweed. Milkweed contains a toxin that doesn’t harm monarch caterpillars, but thanks to this toxin, potential predators have learned that the caterpillars and adult butterflies taste too bitter to eat. Home gardeners plant milkweed to attract monarchs and to make a small contribution to providing habitat.
The USDA Agricultural Research Service reported that monarchs lay eggs on nine different milkweed species, but they have their preferences. Researchers found the most eggs on common milkweed (Asclepias syriaca) and swamp milkweed (A. incarnata). I’ve bought swamp milkweed locally as well as A. tuberosa, which is often called butterfly weed and is on the monarchs’ menu.
Native milkweeds are perennials that die back in winter and return in spring. Non-native, tropical milkweed doesn’t survive our winters, which is a good thing. In warmer parts of the South, tropical milkweed may cause migration delays by not dying back and can also host a parasite harmful to the butterflies. Consider removing it early in the fall if you plant it.
Milkweed unfortunately is tasty to bright orange aphids. Insecticides would harm the butterflies. Knock aphids off with a spray of water or squish them with your gloves. If just a few stems are especially infested, remove and bag those stems.
Visit Lichterman Nature Center and the Butter fly Garden at Memphis Botanic Garden this spring to learn more.