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Scientific name: Anthophyta: Dicotyledonae: Gentianales: Apocynaceae: Asclepias syriaca
Common Name: Information Sheet, Common Milkweed
Photographer: E. M. Barrows
Identifier: E. M. Barrows
Information Sheet, Common Milkweed
Asclepias syriaca Linnaeus (= Common Milkweed, Silkweed, Herre á Coton and Cochons de Lait (in Quebec)
(To see more illustrations of this plant, please use keyword milkweed on this Website.)
[Latin after Aesculapius, the God of Medicine; syriaca, Syrian, after Carlos Linnaeus erroneous supposition that this species originated in Syria.
Linnaeus was fooled because people brought this species from North America to Southern Europe by his time.]
[milkweed, after the milky sap of many milkweed species]
(Fernald 1950, 1174; Kricher & Morrison 1998, 342, 397)
This beautiful perennial, herbaceous, clonal plant is native to Western New Brunswick through Saskatchewan and south through Georgia, Tennessee, Iowa, and Kansas. This plant is attractive in its own right, but it is of additional interest because of all of the fascinating arthropods that associate with it, and its human food value. This species can be common in open areas. Some people grow it in wildflower gardens, such as the one at Rock Creek Park Nature Center, Washington, D.C.
Asclepias syriaca variety kansana has follicles densely covered with subulate-filiform processes 310 mm long, and occurs in Iowa, Nebraska, Missouri, and Kansas. Asclepias syriaca forma leucantha Dore has white flowers.
Asclepias syriaca is abundant in Michigan where it is a major honey plant. I knew it as a child in Michigan as a easily recognizable plant with large leaves, milky sap, and umbels of fragrant pinkish flowers that feed many beneficial insects including bees, butterflies, and wasps. It is a delight to see Great Spangled Fritillaries, Monarch Butterflies, fuzzy yellow-and-black bumble bees and other insects sipping its nectar. This species blooms from June through September. Its fruits are technically follicles (colloquially called pods). Each follicle has about 100 seeds, each attached to a pappus (= a Santa Claus or parachute). In 2001 at a yard sale, I bought a beautiful oval, walnut frame with a large faded Cecropia moth and some beetles resting on a bed of pappi, probably from this species. The seller said that a pharmacist framed the insects in the 1930s.
The sap and other parts of this milkweed are toxic, and Humans should not eat them without proper cooking.
I wanted to have Common Milkweeds in my garden to enjoy them and their animal associates and feed Monarch Butterflies. In 1992, I obtained some plants from a roadside in Garrett County, Western Maryland. I nurtured the plants in pots, and put them into the ground in 1993. The plants formed a clump and flowered in 1994, and then they started spreading by underground stems in my front yard. These stems are from about 10 inches through 1 inch below the surface of the ground. In 2001, some plants grew about 7 feet tall and shaded my tomatoes too much, but I allowed them to remain because they were so attractive. In 2002, about 100 shoots popped up in my front yard. I pulled out, or dug up, most of them, and left the remaining shoots where I wanted them to grow and flower. As the years go by, Ill let the shoots develop where I want them, away from the tomatoes, etc. In 2002, the first flower opened on 8 June in my garden. From 19942001, I usually had a few Monarch larvae on my plants. In 2001, I saw a Monarch laying eggs on my plants, but found only one larvae on them during the entire season. In 2002, I saw two Monarchs laying eggs on my plants. I found no larvae on the plants. However, I placed a female in a cage, and she laid eggs on AS leaves. I released some of the Monarchs and donated others to the GU Ecology Lab for studies on butterfly learning. Scores of Monarch larvae consumed leaves of A. curassavica, AS, and A. tuberosa and at least 40 adult Monarchs (based on marked individuals) flew in my garden in 2007. I found the last large Monarch larva in my garden in early October 2007.
On our long field trip in Forest Ecology, we study AS patches on Backbone Mountain, WV. Since 1994, we visited the same Common Milkweed patch each year in late September. Depending on the year, we found none through many Monarch larvae and pupae in this patch. In 1998, we found many larvae and several pupae; 1999, no larvae or pupae; 2000, several larvae; 2001; several larvae. In 2001, we also watched a straw-colored orb-web spider wrap a large katydid with silk and paralyze her with her bite. I hypothesize that we are more likely to find larvae and pupae in late September after cooler summers, rather than warmer ones.
Some arthropod associates of Common Milkweed are:
Danaus plexippus (Linnaeus), 1758 (the Monarch Butterfly, our National Insect, Nymphalidae) feeds on milkweeds as larvae, and sips their nectar as adults. Monarchs greatly depend on AS for food. As Monarchs migrate north from Mexico in the spring, females lay eggs on newly emerging Common Milkweed shoots and those of other milkweed species. Later in the season females probably lay eggs on this species throughout its range. Large Common Milkweed patches are significant food sources for Monarchs in fields, mountain meadows, and other habitats. Because Common Milkweeds can be scarce in urban areas, it is desirable to grow them for Monarchs and other animals in suburban and urban wildflower gardens.
Arctiid moths, European Earwigs, noctuid Moths (Owlet Moths, Noctuidae), and pyralid moths consume Common Milkweed nectar, primarily at night.
Euchaetes egle (Drury) (Milkweed Tiger Moth, MTM, Arctiidae) feeds on Common Milkweed as caterpillars, which resemble little poodles with black, orange, and white hairs. In July 2000, I moved about 50 small caterpillars onto one large Common Milkweed plant. They were feeding on my potted A. curassavica and ate most of its leaves. In a day, the caterpillars grouped together on the underside of one AS leaf. They disappeared in a few days before I could photograph them.
Eurytides marcellus (Cramer) 1777 (Zebra Swallowtail, Papilionidae) is a large black, blue, red, and white butterfly that consumes Common Milkweed nectar.
Harrisina americana (Félix E. Guérin-Méneville) (Grapeleaf Skeletonizer Moth, Sessidae) is a black moth that consumes Common Milkweed nectar.
Oncopeltus fasciatus (Dallas) (Large Milkweed Bug, Lygaeidae) is a handsome black, orange, and white insect which feeds on milkweed fruits and seeds. Nymphs (immatures) often group together.
Satyrium calanus (Hübner) 1809 (Banded Hairstreak, Lycaenidae) is a small silvery gray butterfly with black, blue, red, and white markings that consumes Common Milkweed nectar.
Tetraopes tetraophthalmus (Forster) (Red Milkweed Beetle) is a beautiful beetle that eats Common Milkweed roots. It evidently causes little harm to my plants. I find none through a few on my plants each year.
Xylocopa virginica virginica L. (= Virginia Carpenter Bee, Giant Carpenter Bee) consumes nectar from Common Milkweed flowers.
Relationships to Forests
Common Milkweeds grow in forest openings and along forest edges. Pollinators of forest plants (e.g., bumble bees, butterflies, and moths) obtain nectar from this plant. Lepidoptera, including the Milkweed Tiger Moth and Monarch, feed on its foliage. The Great Spangled Fritillary which feeds on forest violets as larvae, obtains nectar from Common Milkweed.
Common Milkweed grows easily from seeds or field-collected plants. It requires full sun, and can live in moist, fertile soil through dry somewhat unfertile soil. It is best to allow this plant to mature after it flowers, when it ripens its fruit and supplies resources to its underground stems. After it flowers in my garden, I cut unwanted shoots to the ground, and leave some to strengthen roots and subterranean stems. It is wonderful to leave some shoots with follicles to enjoy over the cold seasons. A pleasant sight is a breezes blowing seeds with their silky, white pappi out of follicles.
E.M.B. (2002, updated October 2007)