The feet or mouthparts of flower-visiting insects, such as bees, wasps, and butterflies, slip into one of the five slits in each flower formed by adjacent anthers.

The seeds, which are arranged in overlapping rows, bear a cluster of white, silky, filament-like hairs known as the coma[13] (often referred to by other names such as pappus, "floss", "plume", or "silk").

[11][15] Milkweeds are also the larval food source for monarch butterflies and their relatives, as well as a variety of other herbivorous insects (including numerous beetles, moths, and true bugs) specialized to feed on the plants despite their chemical defenses.

[5] Milkweeds use three primary defenses to limit damage caused by caterpillars: hairs on the leaves (trichomes), cardenolide toxins, and latex fluids.

[17][18][19] Research indicates that the very high cardenolide content of Asclepias linaria reduces the impact of the Ophryocystis elektroscirrha (OE) parasite on the monarch butterfly, Danaus plexippus.

For example, A. curassavica, or tropical milkweed, is often planted as an ornamental in butterfly gardens outside of its native range of Mexico and Central America.

[22] This is thought to adversely affect migration patterns, and to cause a dramatic build-up of the dangerous parasite, Ophryocystis elektroscirrha.

[24] Because of this, it is most often suggested to grow milkweeds that are native to the geographical area they are planted in to prevent negative impacts on monarch butterflies.

The Miwok people of northern California used heart-leaf milkweed (A. cordifolia) for its stems, which they dried and used for cords, strings and ropes.

Milkweed floss is incredibly difficult to spin due to how short and smooth the filaments are, but blending it with as little as 25% wool or other fiber can produce workable yarn.

During World War II, more than 5,000 t (5,500 short tons) of milkweed floss was collected in the US as a substitute for kapok in life jackets.

[35] Asclepias is also known as "Silk of America"[36] which is a strand of common milkweed (A. syriaca) gathered mainly in the valley of the Saint Lawrence River in Canada.

[41] Many milkweed species also contain cardiac glycoside poisons that inhibit animal cells from maintaining a proper K+, Ca2+ concentration gradient.