Milkweed: Major pillar of North American ecosystems & high-performance insulator
Common milkweed (asclepias syriaca), also known as American Silkweed or Swallow-Wort, is a highly important plant native to most of North American regions. It colonizes meadows, unused fields, vacant lots and even roadsides.
Nature enthusiasts and even novices can easily recognize milkweed. Whether at the flowering stage with its spherical flower umbels or when its seed pods open and release their snow white silks, milkweed just catches the eye at all stages of its life cycle.
Common milkweed is the best known and most widespread species of the Asclepiadoideae subfamily, itself a member of the Apocynaceae genus, which includes more than 2000 species worldwide. Common milkweed covers a vast native territory, from Southern Canada to Texas from north to south, and from Oregon to Nova Scotia from west to east. Common milkweed is currently farmed commercially in Canada and Northeastern USA for the insulating, hydrophobic, rot-resistant, hypoallergenic, antibacterial, and lipophilic (oil and fuel absorbent) white silk contained in its seed pods.
13 species of milkweed are native to Canada:
- Common milkweed, with pink flowers (Native from Saskatchewan to Newfoundland)
- Swamp milkweed, or rose milkweed (asclepias incarnata), with purple flowers
- Butterfly milkweed (asclepias tuberosa), with orange flowers
- Poke milkweed (asclepias exaltata), with white flowers
- Showy milkweed (asclepias speciosa)
- Prairie milkweed (asclepias hirtella)
- Woolly milkweed (asclepias lanuginosa)
- Oval-leaved milkweed (asclepias ovalifolia)
- Whorled milkweed (asclepias quadrifolia)
- Sullivant's milkweed (asclepias sullivantii)
- Redring milkweed (asclepias variegata)
- Green-comet milkweed (asclepias virdiflora)
A gold mine for pollinators
The abundance and diversity of insects visiting the milkweed is not due to chance:
- It is overflowing with nectar rich in sugars (3%).
- This pollen is also renewed during the lifetime of the flower, which is unusual.
- The blooming period is also unusually long compared to other plants, about 4 weeks for a colony.
Some of the many pollinators visiting the milkweed flowers.
Host plant of the monarch butterfly
Milkweed is the exclusive host plant of the monarch butterfly (Danaus plexippus). Their symbiotic relationship dates back millions of years and is so complex that science has not yet uncovered all its mysteries.
- The sap of the milkweed naturally contains substances called cardenolides, toxic to most animals, including several predators and parasites of the monarch.
- Monarch females lay eggs exclusively on milkweed plants along their migratory route, from Mexico to Canada.
- The caterpillars feed on the leaves of the milkweed to self-medicate against parasites and become toxic to several of their potential predators.
- The caterpillars form their chrysalis near their birth milkweed plant, where a butterfly hatches that will feed, among other things, on the nectar of the milkweed (aiding pollination), but also other flowers depending on the time of summer it hatches.
The peculiarity here is that instead of breaking down or excreting the toxins from its food, as is the case with many similar animals, the monarch larva accumulates it in its tissues and even retains it after its transformation into a butterfly. The concentration of cardenolides in a monarch caterpillar/butterfly is thus much higher than in a milkweed plant, making them effectively toxic to many predators and parasites. Some other specialist insects (bugs, longhorn beetles, milkweed beetle, and milkweed aphid, etc.) have also developed the same evolutionary strategy, displaying the same colors as the monarch.
As 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 the attacks of its herbivore predators, of which the monarch caterpillar is part. Also, its reproduction depends partly on the pollination carried out by adult monarchs feeding on the abundant nectar of its flowers.
It thus becomes almost impossible to describe the monarch without mentioning milkweed, and vice versa.
American Silk as a High-Level Thermal Insulator
The fibers attached to the milkweed seeds are commonly referred to as American Silk or Quebec Silk. These hollow, nearly perfectly round microtube-like fibers trap air and create a surprising thermal, acoustic, and waterproof barrier for a plant material. When milkweed silk is used as padding or aligned in a textile insulation membrane, the air contained in the inner portion (lumen) of the fibers adds to the layers of air trapped between the fibers. This unique property creates a perfect barrier against heat transfers, making it possible to manufacture thin, lightweight outdoor accessories with a level of thermal insulation that rivals synthetic or animal-based materials.
Another interesting property that makes the fibers even more suitable as an outdoor clothing lining: they are naturally coated with a wax that makes them hydrophobic, i.e., they completely repel water. So, in addition to keeping warm, clothes insulated with milkweed keep dry! This is an impressive advantage over other textile insulators available on the market, such as down, polyester, or wool, which easily soak up water and retain moisture, while having a much higher ecological and ethical impact.
And this advantage is twofold: Milkweed repels both external moisture (snow, rain, etc.) and internal moisture (sweat).
Other Industrial Uses
Milkweeds have been used in various ways throughout history. Native Americans found several uses for this plant, from making rope and fabric from the plant's strong fibers, to using the milky latex to treat skin problems.
Life Vest filling
A bit of history: During World War II, when the supply of Asian kapok is blocked by Japan, it is harvested on a large scale in Canada and the United States to extract a textile fiber, used to fill the flotation vests of sailors and aviators. Indeed, the hydrophobic properties of milkweed make it float for up to 8 hours straight. Of course, all this was before the arrival of synthetic materials. This potential has unfortunately been abandoned today.
Oil Spill Absorbent
The same goes for the multitude of other economic outlets for milkweed. One of the most promising currently is undoubtedly as a high-level absorbent for oil spills. Indeed, the same tubular structure of the fibers that gives them their insulating property also makes them lipophilic, i.e., capable of retaining oily substances. Needless to say, this characteristic would be very useful for containing oil product spills in aquatic environments. Weight for weight, milkweed absorbs 5 times more diesel than the material currently most used on the market for this purpose (polypropylene), in addition to floating perfectly and absorbing no water! Milkweed is a miraculous alternative at this level, especially when you think of the irony of the current industry of oil absorbents, which are made from... oil!
An American company, Ogallala, uses milkweed combined with down in their bedding and pillow filling. Naturally hypoallergenic, milkweed repels moisture, dust, and mites. It gives Ogallala's products a quality superior to the competition, and users a sleep better than their peers!
The oil extracted from milkweed seeds is closely considered for its potential as a base for cosmetics, such as skin lotions or sunscreen. With a chemical process, it is indeed possible to transform the triglycerides of milkweed oil into compounds that absorb UV rays. Perhaps in a somewhat more distant future, but still very promising!
The milkweed revolution is here, all around us... all that remains is to harvest it!