The iconic orange and black markings of monarch butterflies (Danaus plexippus) might make them the most recognizable of all butterfly species. Each spring, the monarchs’ migration from Mexico to the northern United States and Canada brings them through central North Carolina.
But could we be witnessing the final migrations of these beloved backyard beauties? Monarch populations have plummeted more than 80% since the 1990s, and a recent report by the Xerces Society for Invertebrate Conservation and Nature Serve indicates that the North American monarch population, particularly that east of the Rocky Mountains, is vulnerable to extinction. Rapid development of rural land in both Mexico and the United States has destroyed monarch habitats, and widespread use of herbicides has decimated the monarchs’ larval food sources.
The good news is that monarchs are a resilient species and can likely recover if given sustained support along their collective journey.
Most butterfly species hibernate. Only the monarch makes a two-way migration. The monarchs’ journey begins in Mexico’s Sierra Madre mountains, nearly two miles above sea level where millions of monarchs spend the winter in oyamel fir (Abies religiosa) forests. Every March, as days lengthen and temperatures begin to warm, the monarchs begin migrating northward in a wide swath from Texas and New Mexico eastward to the Atlantic Ocean.
Along the way, adult females lay eggs on the leaves of milkweeds (Asclepias sp.), then die. In April and May, the eggs hatch and the caterpillars eat their fill of the milkweed leaves. They pupate, hatch, and continue the migration northward.
Adult monarchs live two to six weeks during the breeding season, but the full migration takes several months. The adults who arrive at the final northern destination are the great-grandchildren of those butterflies that left Mexico in March. The fourth or fifth generation, born in the fall, returns all the way to Mexico by November to overwinter and begin the northward migration the following year. This overwintering generation can live up to eight months.
Sustain the migration
Monarchs lose habitat at a rate of approximately 6000 acres (9.4 square miles) per day due to development. This habitat loss represents the greatest threat to the butterflies’ survival. But pockets of habitat along the migration path can help sustain the monarchs along their journey. Citizens can help conserve the species by doing a few simple things.
1. Plant milkweeds for monarch larvae (caterpillars). Part of providing habitat means planting food sources for both larval and adult insects. Milkweeds are the only food source for larval monarchs, and thus are essential to their survival. The milkweed species recommended for the Southeast include:
• Butterfly weed (Asclepias tuberosa), which grows between 1 and 3 feet tall and offers bright orange flowers from summer through fall.
• Common milkweed (Asclepias syriaca), native to the eastern United States, grows 2-3 feet tall and 1 foot wide, with flowers that range from mauve-pink to white.
• Whorled milkweed (Asclepias verticillata) grows about 2 feet high and blooms slightly later than other milkweed species, nurturing the migratory stragglers. Its flowers are white to slightly green and its leaves are narrower than other Asclepias species.
• Swamp milkweed (Asclepias incarnata) grows 3-4 feet tall and 2-3 feet wide. As the name implies, it prefers moist to wet soils. The flowers are rosy-pink. It has a deep taproot and prefers to be left undisturbed once planted.
All milkweed species prefer full sun (at least 6 hours of direct sun per day), though some, including Asclepias verticillata, can perform with morning sun exposure. All Asclepias species are rich in nectar, attract a variety of pollinators, and are deer-resistant. Asclepias species other than A. incarnata perform well in dry to average soils, though like all newly planted perennials, they must be watered regularly for the first year until established.
Asclepias tuberosa is widely available at local nurseries and garden centers. Some specialty nurseries also carries swamp milkweed. Other varieties may require web searches to track down the plants. Milkweeds may also be started from seed. Native milkweed seed may be obtained from Sow True Seed (www.sowtrueseed.com).
2. Plant nectar-rich plants. Adult monarchs need abundant nectar from a variety of flowers. While milkweeds provide good sources of nectar, other plants, including liatris, tithonia, coneflowers, Joe pye weed, salvias, and zinnias provide excellent sources of nectar to support adults.
3. Avoid pesticides and herbicides. When you see caterpillars munching down the leaves of your plants, don’t spray them. While monarch caterpillars will feed exclusively on milkweeds, they remain susceptible to drift from pesticides applied to other plants. If you are trying to control caterpillars on your vegetable garden, use row covers, cardboard, or other means to keep sprays from drifting onto your nectar-providing plants. Learning to recognize the larval forms of your favorite butterfly species will also help avoid accidental poisoning.
4. Participate in citizen science. Report your monarch sightings to Journey North (www.JourneyNorth.org), a free, internet-based program that tracks seasonal migrations of many different species of wildlife.
5. Encourage schools, clubs, and other organizations to get involved. Providing critical food sources for monarchs can help preserve this beloved species. In this conservation endeavor, every person’s effort is a meaningful contribution.
Featured photo – Monarch on liatris / Prairie Moon Nursery
Amy Hill is a Durham County Master Gardener and blogs about gardening at MissingHenryMitchell.com.