Milkweed Survey Title Graphic

Survey Protocol

Milkweed Photos

Monarch Life Stages

Milkweed Leaf Damage

Monarch Watch


Monarch larvae appear to feed exclusively on milkweeds (Asclepidacae). There are approximately 108 species of Asclepias and several genera of viney milkweeds in North America and Monarch larvae have been observed feeding on many but not all of these species. Milkweeds are perennial plants, growing each spring from rootstock and seeds rather than seeds alone. In the Midwest, milkweeds were historically common and widespread on prairies, but habitat destruction has reduced their range and numbers.

When Monarch larvae ingest milkweed, they also ingest the plants' toxins, called cardiac glycosides. They sequester these compounds in their exoskeletons, making the larvae and adults toxic to many potential predators. Vertebrate predators may avoid Monarchs because they learn that the larvae and adults taste bad and/or make them vomit. There is considerable variation in the amount of toxins in different plants. Some northern species of milkweed contain almost no toxins.

Below we have listed the milkweed species that you are most likely to encounter in the course of this survey. Click on any image and a larger version of the image will appear in a new window.

Asclepias incarnata
(Swamp Milkweed)

Swamp Milkweed has opposite leaves and red to rose-purple flowers that rarely are white. It grows in swamps from New Brunswick to Ontario south to Tennessee and Louisiana.

Asclepias speciosa
(Showy Milkweed)

Showy Milkweed has large opposite leaves and grows 50 to 100 cm tall. Its purple-rose flowers are unusual for the genus. It grows in moist soil on prairies or in sandy soil next to lakes and ponds, ranging from Minnesota west to British Columbia and south to Kansas, Utah, and California.

Asclepias syriaca
(Common Milkweed)

Common Milkweed is the plant many people think about when they hear the word "milkweed." From 60 to 200 cm tall, it has opposite leaves and purple to pink flowers. It grows in prairies, pastures, roadsides, or on the banks or edges of lakes, ponds, waterways, forests, or prairies throughout the Great Plains.

Asclepias tuberosa
(Butterfly Milkweed)

Butterfly milkweed is a perennial plant 30 to 90 cm tall with mostly alternate leaves. Its flowers are usually orange, rarely yellow or red. It grows in sandy or loamy soil in prairies, roadsides, or open woodlands across the Great Plains.

Asclepias verticillata
(Whorled Milkweed)

Whorled Milkweed is 30 to 90 cm tall with very narrow leaves grouped in whorls of 3-7 around the stem. Its flowers are greenish-white. It grows in dry fields and on hills from Maine and Ontario south to Florida, Mexico, and New Mexico.

Asclepias viridis
(Spider Milkweed)

Spider Milkweed is 25-65 cm tall with leaves mostly alternate. Its flowers are greenish-white and reddish-purple. It grows in sandy or rocky calcareous soils in prairies from Ohio to Nebraska and south to Florida and Texas.

Cynanchum laeve
(Blue Vine Milkweed)

Blue Vine is a perennial trailing vine with leaves opposite and heart-shaped. Its flowers are whitish to cream. It grows in sandy, clayey, or rocky calcareous soils of forest margins, thickets, flood plains, or disturbed areas from Pennsylvania to Nebraska and south to Georgia and Texas.

[ Top of Page ]
[ Intro ] [ Survey Protocol ] [ Milkweed Photos ] [ Monarch Life Stages ]
[ Milkweed Leaf Damage ] [ Monarch Watch ]