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.
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.
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.
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.
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.
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.
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.