Milkweed and the Monarch

Growing milkweed to attract and raise monarch butterflies is an easy and rewarding way to give nature a helping hand, and to restore the declining monarch populations.

Photo by Getty Images/Jeff Stefan.

The North American monarch (Danaus plexippus) population has decreased substantially since the 1980s. Though monarchs are not an endangered species, their declining numbers are a cause for concern among conservationists. The primary reason for their decline is thought to be habitat destruction, particularly the destruction of habitat for milkweed (Asclepias spp.) plants. Monarchs depend on milkweed for several vital reasons; adult monarchs feed on the nectar from the flowers, and female monarchs only lay their eggs on milkweeds, because monarch larvae won’t eat any other plant.

Monarchs are large, showy butterflies that attract a lot of interest from the general public for their famous international migration from Michoacán, Mexico, to southern Canada and back. This yearlong cycle, spanning several generations of monarchs, means that these creatures can be found throughout the country, from the northern states bordering Canada, to ever-sunny Florida, and even all the way to the Golden Coast. This wide range means that it’s easy for any gardener to make a difference; growing milkweeds is easy, and hand-raising monarch larvae is likewise straightforward.

The Ins and Outs of Milkweed

Milkweeds are flowering perennials in the genus Asclepias, many of which are native to North and South America. The “milk” in milkweed refers to the white latex inside the plant that oozes out when the stem breaks. This “milk” is the reason that monarchs will only lay their eggs on milkweed plants. Milkweed latex contains cardenolide alkaloids that are harmful to most insects — as well as small birds — but not to monarchs. These alkaloids, which are a subdivision of cardiac glycosides, are molecules that arrest an animal’s heart. Monarchs use milkweed alkaloids as a chemical defense; they eat the milkweed leaves and sequester the alkaloids in their abdomen and wings. The presence of alkaloids make the insect taste bitter and deters predators, who will often spit them out. For example, a bird that swallows a monarch will either regurgitate its prey, or suffer the effects of the cardiac glycosides and die.

Asclepias syriaca - Common Milkweed. Photo by Adobe Stock/annavolotkovska.

Growing milkweed isn’t difficult; they don’t need rich soil, nor do they require extensive tending. When growing milkweeds to attract and raise monarchs, be sure to source seeds and plants from species native to your local area. Some milkweed species, such as common milkweed (Asclepias syriaca), whorled milkweed (A. verticillata), swamp milkweed (A. incarnata), and butterfly weed (A. tuberosa) grow throughout the migration range for monarch butterflies. While butterfly weed has spectacular orange flowers attractive to hungry adult monarchs, it’s common milkweed that attracts female monarchs in particular. You should plant common milkweed to capture eggs and hand-raise larvae, as it’s their favorite to eat.



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