It is often planted in gardens (it is frost-sensitive, requires full sun and well-drained soil and should be regarded as invasive), particularly because it attracts butterflies (Monarch and Swallowtail), but also crab spiders, ladybirds/bugs, bees, wasps, ants and moths. Some feed on the nectar and the plant itself while others feed on the insects attracted to it.
Milkweed not only provides food for the adult Monarch but also a nesting area for eggs and larvae. It can have a deep root system once it becomes established and is then difficult to eradicate from gardens.
The plant is quite toxic because it produces a group of toxins known as cardenolides. The poisons protect the plant against herbivores. However, some animals and the ostrich, are capable of eating the plant without ill effect.
Thus the Monarch caterpillar is among a select few creatures able to graze on the leaves of the milkweed. It manages to sequester and store poisons so that the butterfly into which it develops is protected from predators.
The female Monarch butterfly lays her eggs on the underside of the leaves where they hatch in about 5 days. The young caterpillar chews itself out of the shell which it then eats as its first meal.
Stems contain a strong, silky bark fibre formerly used for sewing. The milky latex reportedly effective in removing warts. Seed hairs formerly used as tinder and to stuff pillows and mattresses.
A leaf infusion, taken by mouth, is used to treat intestinal troubles (diarrhoea and stomach pain) in children and, given per rectum, as a purgative. Dried powdered leaf is inhaled as a snuff for the relief of headache, coryza and tuberculosis.