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Monarchs and milkweed: A critical team

How gardeners can help save the monarch butterfly

Each fall, a dazzling natural phenomenon occurs throughout North America as millions of monarch butterflies migrate to Mexico and California from areas of the northern United States and Canada for the winter. Their return flight in the spring when weather conditions in the north are more favorable make this the only known complete migration by an insect. However, it is not without threat.

Habitat loss in overwintering spots in Mexico and throughout the spring and summer breeding range threaten the monarch butterfly and its one-of-a-kind journey, according to Dr. Chip Taylor, Monarch Watch director and a professor of entomology at the University of Kansas.

Development of factories, shopping centers, and subdivisions and widespread agricultural and roadside management use of herbicides has caused the decline of milkweed a plant with which the butterfly has a co-evolutionary relationship and nectar sources. Monarch caterpillars will feed on the leaves of milkweed plants, but adults will take nectar from the flowers of milkweed and other plants.

"We are losing 6,000 acres a day - or 2.2 million acres per year - of habitat due to development. That is equal to the area of Delaware and Rhode Island alone. In my 17 years of running this program, it equals the area of Illinois!"

Because the remaining milkweed habitats, pastures, hayfields, forest edges, native prairies and urban areas are insufficient to sustain monarch populations, Monarch Watch urges gardeners, homeowners and citizens to take action.

Monarch butterfly feeds on oval-leaf milkweed (Asclepias ovalifolia). Photo by Andy and Sally Wasowski.

"We want people to plant milkweed to compensate for this loss of habitat," says Dr. Taylor. Monarch Watch's Monarch Waystation Program has so far certified 2,600 registered monarch waystations in home gardens, at schools, businesses, parks, zoos, nature centers, along roadsides and on other unused plots of land. Without a major effort to restore milkweeds to as many locations as possible, according to Monarch Watch the monarch population is certain to decline to extremely low levels.

In North America there are 108 species of Asclepias, 30 of which monarch butterflies have a tendency to preferentially use, says Dr. Taylor. Their distaste for some species can be explained by one particular plant's hairiness or the high amount of latex in another.

"A lot of it has to do with a plant's seasonality - for example, the quality of the leaves or flowers at the time the female monarch is laying eggs," he says. "For instance, here in the Midwest, there are 3 or 4 milkweeds that the butterflies will only lay eggs on when they are coming up in the first generation, not in subsequent generations."

Much of it is simply chemistry, says Dr. Taylor.  If the leaves are getting old or spotty, if they just don't have the right chemistry, "the monarchs will search for something that does. It is all about the chemistry of the flowers and of the leaves."

This co-evolutionary relationship is not rare in the plant-butterfly world. Most butterflies are confined to one or two families of plants, according to Dr. Taylor. "No other butterflies use milkweed as a host plant because they can't deal with the toxicity of the plant. A few other moths use it, but the plant has evolved away from most generalist insects."

Fourleaf milkweed (Asclepias quadrifolia) has stunning, fragrant flowers and is native to states as far west as Arkansas and as far east as New York. Photo by W.D. Bransford

For those wishing to help combat the loss of habitat for these remarkable butterflies by growing milkweed, Wildflower Center director of horticulture Andrea DeLong-Amaya says that planting seasons vary.

"For us here in the South, fall through winter is good for planting native milkweeds. Further north, gardeners would be best off waiting until spring."

As for growing milkweed from seed, she says she has done so successfully but that germination and keeping them going is easier with some species than with others.

As varied are the species of Asclepias are the recommendations for their care in the garden, according to DeLong-Amaya. "Generally milkweeds prefer full sun and good drainage. However, there are exceptions. Asclepias incarnata (swamp milkweed), for example, prefers moist locations."

Milkweeds are essential for feeding the caterpillars of monarchs, but as adults the butterflies will take nectar from a wide range of flowers, says DeLong-Amaya.

"Incorporating a variety of plants in one's garden will increase the diversity of pollinators in general and will surely accommodate the needs of monarchs," she says.

She reports that in Texas they are just now beginning to see monarchs that are making their way to Mexico.

Their keen sense of direction - possibly partly due to geomagnetic orientation, says Dr. Taylor - will help them find their way back next spring. Let's hope they find plenty of milkweed to feed upon when they return. - C. Procopiou

For more information about Monarch Waystations and other monarch information, visit www.monarchwatch.org.

© 2016 Lady Bird Johnson Wildflower Center