Milkweeds should never be considered just another weed. They in fact have very important ecological roles to play. Without them, monarch butterflies would be deprived of a plant essential to their survival.
Milkweeds, previously classified in the family Asclepiadaceae, are now grouped in the family Apocynaceae.
In Québec, there are 4 native species:
Asclepias syriaca (Common milkweed)
Asclepias incarnata (Swap milkweed)
Asclepias exaltata (Poke milkweed) – uncommon species
Asclepias tuberosa var. interior (Butterfly milkweed) – endangered species in Québec
Milkweeds are perennials with flowers arranged in umbels. We call them milkweed because of the milky-white latex-based sap that flows out when the plant is damaged. That latex contains substances that are toxic for most animals. Milkweeds produce fruit called follicles, which when ripe split open longitudinally, releasing their many seeds to the wind. These seeds have long silky hairs, sometimes called floss, which facilitate their dispersal.
A number of milkweed species contain substances that act on the heart. As a result, all species and all parts of the plant are considered potentially toxic for livestock and for humans. And latex may cause an allergic reaction in some susceptible people.
The nectar of milkweed flowers attracts numerous insects and pollinating animals such as bees, wasps, butterflies, beetles, flies and hummingbirds. Besides pollinators, milkweeds are visited by predatory and parasitic insects that are very useful both in the garden and in agriculture.
Some insects feed, at one stage or another, exclusively on milkweeds. That’s the case with the monarch caterpillar (Danaus plexippus plexippus). Adults must lay their eggs directly on these plants so that young caterpillars have access to the food they need to live. Which is why the survival of the monarch is closely linked to milkweeds.
The decline of the monarch and of milkweeds
Climate change is making itself felt over the entire monarch migration area, notably at the wintering grounds in Mexico, strongly affecting the populations of this butterfly. But the loss of natural habitats and the eradication of milkweed by pesticides in agricultural areas are the principal causes of the monarch decline. The problem is, despite the importance of native milkweeds for pollinators and for monarchs, these plants are often perceived as weeds and are wiped out in fields and along roadsides.
The loss of natural habitats and the important reduction in milkweed populations, essential to the breeding of monarchs, demonstrate the urgent need to protect the remaining milkweed populations and to encourage restoration activities.
With the aim of safeguarding the monarch butterfly, research and conservation programs such as Monarch Watch, and awareness-raising and community science programs like the Insectarium’s Mission Monarch, monitor the populations of this butterfly. These initiatives also promote the planting of milkweed in gardens, as does the Space for Life My Garden program.
Milkweed has been used by the First Nations as a medicinal plant, as food, and to make rope.
In the early 20th century, a number of efforts were made to commercialize the plant, from extracting the latex to using the silky hairs in the manufacture of various textile products. During the Second World War, the “floss” was used as stuffing for life jackets. That floss, which is in fact made of microscopic tubes, has good flotation and insulating properties.
Long looked on in agriculture as just a weed, the common milkweed (Asclepias syriaca) is enjoying a revival because of the qualities of its fiber, which is produced from the silky hairs of the seeds. It bears the nickname “silk of America” because it produces a flexible, resistant and hydrophobic fiber that offers excellent qualities as acoustical, but especially thermal, insulation.
Today, the silk from commercially grown milkweed is used for stuffing quilts and pillows, in the textile industry for making moisture-resistant warm clothing, in the production of thermal and acoustical insulation, and even as an absorbent material for use in oil spills.