Milkweed: Major pillar of North American ecosystems & high-performance insulator
Common milkweed (Asclepias syriaca), sometimes called American silk, is a plant native to North America that colonizes unused fields, vacant lots and even roadsides.
Nature lovers and even beginners recognize it easily. Whether in bloom, with its almost perfectly spherical flower umbels, or when its pods split open to release seeds and white floss, milkweed catches the eye of anyone passing by.
Common milkweed is the best-known and most widespread species of the subfamily Asclepiadoideae, itself part of the dogbane family (Apocynaceae), which includes more than 2,000 species. Common milkweed's natural range runs from Québec to Texas, north to south, and from Oregon to Nova Scotia, west to east. It is the species grown commercially in Canada for its white floss: insulating, water-repellent, rot-resistant, hypoallergenic, antibacterial and absorbent.
In Québec and Eastern Canada, four milkweed species are native:
- Common milkweed (Asclepias syriaca), with pink flowers
- Swamp milkweed (Asclepias incarnata), with mauve flowers
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Butterfly milkweed (Asclepias tuberosa), with orange flowers
- Poke milkweed (Asclepias exaltata), with white flowers
A gold mine for pollinators
The abundance and diversity of insects that visit milkweed is no accident:
- It overflows with sugar-rich nectar (3%).
- Its pollen is also renewed over the life of the flower, which is unusual.
- Its blooming period is also unusually long compared with other plants, about 4 weeks for a colony.
A few of the many pollinators that visit milkweed flowers.
Host plant of the monarch butterfly
Milkweed is the exclusive host plant of the monarch butterfly (Danaus plexippus). Their symbiotic relationship goes back millions of years and is so complex that science has yet to unravel all of its mysteries.
- Milkweed sap naturally contains substances called cardenolides, which are toxic to most animals, including many of the monarch's predators and parasites.
- Female monarchs lay their eggs exclusively on milkweed plants spread along their migration route, from Mexico to Canada.
- The caterpillars feed on milkweed leaves to self-medicate against parasites and to become toxic to many of their potential predators.
- The caterpillars form their chrysalis near the milkweed plant they were born on, where a butterfly emerges that will feed on milkweed nectar, among others (helping pollination), as well as other flowers depending on the time of summer it emerges.
What sets the monarch apart is that instead of breaking down or excreting the toxins in its food, as many animals with similar behaviour do, the monarch larva accumulates them in its tissues and keeps them even after it transforms into a butterfly. The concentration of cardenolides in a monarch caterpillar or butterfly is therefore much higher than in a milkweed plant, making them effectively toxic to many predators and parasites. A few other specialist insects (milkweed bugs, the milkweed longhorn beetle, the milkweed leaf beetle, the milkweed aphid, etc.) have developed the same evolutionary strategy, sporting the same colours as the monarch.
Since the relationship is symbiotic, milkweed also shows signs of co-evolution with the monarch and other herbivores. The plant seems to heal faster and faster from attacks by its herbivorous predators, the monarch caterpillar among them. Its reproduction also depends in part on pollination by adult monarchs feeding on the abundant nectar of its flowers.
It becomes almost impossible to describe the monarch without mentioning milkweed, and vice versa.
Milkweed floss as a high-performance thermal insulation
The fibres attached to milkweed seeds are what we commonly call milkweed floss, American silk or Québec silk. These hollow fibres, shaped like almost perfectly round micro-tubes, trap air and create a thermal, acoustic and water-resistant barrier that is surprising for a plant material. When milkweed floss is used as a filling or laid out as an insulating textile membrane, the air held inside the fibres (the lumen) adds to the layers of air trapped between the fibres. This unique property creates an ideal barrier against heat transfer, making it possible to build outdoor accessories that are thin, light, and whose thermal insulation holds its own against synthetic or animal-based materials.
Another interesting property makes the fibres even better suited as a lining for outdoor clothing: they are naturally coated with a wax that makes them hydrophobic, meaning they repel water. So on top of keeping you warm, milkweed-insulated clothing keeps you dry! That is an impressive advantage over the other textile insulations on the market, such as down, polyester or wool, which soak up water easily and hold on to moisture, while having a much heavier ecological and ethical footprint.
And the advantage is twofold: milkweed repels moisture from the outside (snow, rain, etc.) as much as from the inside (sweat).
Other industrial uses
Flotation material
A bit of history: during the Second World War, when the supply of kapok from Asia was cut off by Japan, milkweed was harvested on a large scale in Canada and the United States to produce a textile fibre used to fill the life vests of sailors and airmen. Thanks to its hydrophobic properties, milkweed floats for up to 8 hours straight. All of this was before synthetic materials came along, of course. Unfortunately, this potential has since been abandoned.
Oil spill absorbent
The same goes for milkweed's many other economic uses. One of the most promising today is without a doubt as a high-performance absorbent for oil spills. The same tubular fibre structure that gives it its insulating property also makes it lipophilic, meaning it can hold oily substances. It goes without saying that this characteristic would be very useful for containing petroleum spills in aquatic environments. Weight for weight, milkweed absorbs 5 times more diesel than the material most commonly used for this purpose today (polypropylene), while floating perfectly and absorbing no water at all! Milkweed is a remarkable alternative here, especially when you consider the irony of today's oil absorbent industry, whose products are made from... oil!
Bedding fill
An American company, Ogallala, uses milkweed blended with down as the fill for its bedding and pillows. Naturally hypoallergenic, milkweed repels moisture, dust and dust mites. It gives Ogallala's products an edge over the competition, and its users a better night's sleep than everyone around them!
Cosmetics
The oil extracted from milkweed seeds is being closely studied for its potential as a base for cosmetics such as skin lotions or sunscreen. Through a chemical process, it is possible to turn the triglycerides in milkweed oil into compounds that absorb UV rays. Perhaps a little further off, but very promising all the same!
The milkweed revolution is here, all around us... all that's left is to harvest it!
