The Secret Life of Milkweed: Beyond the Monarch

While the monarch butterfly’s dramatic 90% population decline and pending endangered status get all the press, milkweed is far more than just a single butterfly’s nursery. In reality, these native perennials act as the biological bedrock for entire mini-ecosystems. Their nectar-rich, vanilla-scented flowers are an irresistible buffet for a massive variety of native wildlife, including sweat bees, leafcutter bees, and less famous milkweed butterflies like queens and soldiers.

Beneath the surface, milkweed’s extensive, deep root systems work tirelessly to enhance soil quality, increase water infiltration, and bind the earth together. Acting as natural subterranean filters, these robust root structures actively reduce stormwater runoff and safeguard local water sources from harmful agricultural and urban pollutants. By weaving these plants into our developed landscapes, we restore the foundational ecological layers that keep local environments stable and resilient against severe weather extremes.

A Vital Link in the Great Green Food Web

Far from being a simple “weed,” milkweed anchors a complex food web that supports hundreds of insect species across North America. The plant’s famous milky sap contains toxic compounds called cardenolides (or cardiac glycosides) that serve as a natural chemical defense. While monarch caterpillars have uniquely coevolved to tolerate, isolate, and store these toxins to make themselves unpalatable to birds, a whole community of specialized bugs, beetles, and spiders thrives alongside them in the milkweed patch. This dense concentration of insect life creates a critical, high-protein foraging ground for terrestrial birds like quail, pheasants, and native upland songbirds, particularly during the nesting season when chicks require abundant insect prey. Consequently, a single patch of milkweed ripples positive effects outward, driving regional biodiversity and stabilizing the predatory relationships essential to a healthy ecosystem.

Cultivating a Lifeline in Your Backyard

You can actively fuel this vibrant ecosystem by swapping out resource-intensive turf grass for native milkweed varieties like Butterfly Weed (Asclepias tuberosa) or Swamp Milkweed (Asclepias incarnata). However, a truly resilient habitat requires planting a diverse matrix of other native flowering plants alongside your milkweed to sustain adult pollinators throughout the year.

While caterpillars are specialist herbivores that depend solely on milkweed leaves, the adult butterflies, bees, and beneficial insects need a continuous, multi-season supply of nectar to fuel their high-energy flights and taxing migrations. Integrating regional wildflowers like coneflowers, asters, and goldenrods ensures that food sources remain abundant from early spring through late autumn when milkweeds begin to die back.

Because tropical milkweed does not naturally die back in the winter in southern climates, it accidentally disrupts natural migratory cues and triggers heavy accumulations of OE (Ophryocystis elektroscirrha), a debilitating protozoan parasite that cripples adult butterflies. By establishing a garden composed of at least 70% regional plants, arranging milkweed in dense clumps so caterpillars can easily forage, and selecting species that ensure multi-season blooms, you provide safe, reliable fuel stops for both iconic migratory species and the vital, unsung backyard creatures that keep our environment functional.

Preserving the Future of Texas Flora

Local conservation efforts are vital to ensuring these complex habitats survive the compounding pressures of urbanization and agricultural monoculture. At the forefront of this regional mission, the San Antonio Botanical Garden’s conservation department actively stewards over a dozen species of Asclepias and counting within their collections. This active repository allows researchers to study the distinct growth requirements of rare, threatened, and under-represented Texas milkweed varieties that are often overlooked by mainstream commercial horticulture. By implementing dedicated research, seed banking, and strategic propagation initiatives, the conservation department serves as an integral lifeline for preserving fragile native flora. Through these tireless regional efforts, we ensure that both the milkweed patches and the wild, interconnected communities relying on them will continue to thrive across the changing Texas landscape.

NOTES USED

The monarch butterfly population has decreased by 90% in the past 20 years! This beautiful pollinator is now at risk of endangered status under the Endangered Species Act according to the United States Fish and Wildlife Service.

The monarch butterfly is a beautiful species that undergoes an incredible migration, travelling over one thousand miles from North America to Mexico in order to go through a hibernate-like state called diapause.

Pollinators rely on diverse plant communities in their native habitat which often consists of meadow plant species. For future generations to survive, monarchs require species of milkweed to act as their larval host plant.

Due to urbanization and the agricultural transformation of pollinator meadows into monoculture fields, milkweeds and these other crucial plants have been completely eradicated in certain areas of the continent. It is important to understand why saving monarch butterflies and pollinator plants is vital to the preservation of natural ecosystems, and how we can all contribute.

Milkweeds act as host plants to monarch butterflies. They lay their eggs only on milkweed plants because milkweed is the only food the caterpillars can eat. Without the presence of milkweed, monarch caterpillars have no food source and the population suffers.

While monarchs rely on milkweeds to support their larval stage, as adults they also rely on having abundant nectar sources from other flowering plants to provide them with energy

Monarchs can travel 50-100 miles a day, exerting significant energy in the process. The butterflies must have enough sources of nectar to frequently replenish this energy loss.

Milkweeds are an important nutrient source to bees as well as other butterfly species. They have conspicuous flowers during the summer months that can add a pop of color to native plant gardens. There are milkweed species that thrive in many different habitats but many prefer full sun with moist soil and can be found in pastures, croplands, and natural areas such as prairies.

Pollination allows for the formation of fruits and seeds that are crucial to the sexual reproduction of plants. Without pollination, genetic diversity is reduced, making plants less resilient to disease and environmental changes.

Monarch butterflies spend their lives migrating from Canada and the United States to Mexico – some individuals travelling up to 3,000 miles. Recently this journey has become more treacherous and less successful due to habitat loss, illegal logging,  widespread use of pesticides, livestock raising, and deforestation.

Although the task seems daunting, it is not too late to help monarch butterflies. By planting milkweed, you’ll be supporting monarch butterflies, attracting beneficial pollinators, and adding some color to your garden. But, not all milkweeds are made alike.

Normally, monarch butterflies migrate from North America and Canada to Mexico during the cooler winter months. Milkweed species native to North America, like Asclepias tuberosa, die back each fall which helps promote butterfly migration. With no milkweed around to feed on, butterflies head south in search of a new food source.

The monarchs need our help, and you can help by planting milkweed and other wildflowers that provide the necessary food and nectar for these species.

If you live in the United States, we recommend you do not plant this species of milkweed. Tropical milkweed (Asclepias curassavica), which is sold at many retail nurseries, is not native to the United States. Plus, research is showing that its long bloom time may have some negative effects on monarch migration and can even be a source of disease spread within monarch populations. For these reasons, we recommend avoiding tropical milkweed and instead opting for milkweed species that are native to your region. Tropical milkweed (Asclepias curassavica), is not native to the United States or Canada, but since it is attractive and easy to grow, it is often the most widely available milkweed at commercial nurseries.

Tropical milkweed is native to the tropics and it is adapted to grow year-round. When tropical milkweed is planted in the southern United States including in places like Houston, these plants continue to flower and produce new leaves throughout the fall and winter. This can cause potential negative effects on monarchs including:

1. Decreased fall migration: with the availability of milkweed during a time that is not naturally available, monarch fall migration is jeopardized. With a steady food source, the need to migrate decreases.
2. Increase in infections: continuously breeding on the same plants can lead to a build-up of Ophryocystis elektroscirrha (OE) infection. Migration decreases OE infections.

Native plants support local ecologies

Choosing native plant varieties promotes healthy and sustainable landscapes and attracts native wildlife. Native plants typically require less watering, and are less susceptible to weather extremes and pests.

For those who already have tropical milkweed: If you have already purchased tropical milkweed, you can help monarchs by remembering to cut back your plants in mid October each year to promote monarch migration.

While there isn’t currently a simple answer to this question, the more milkweed you plant, the better!

In general, the number of milkweed plants is less important than the fact that you are planting milkweed in the first place!

If you’re looking for some other tangible goals to help monarchs, you can:

• Set a goal of having your garden be 70% native plants.
• Plant milkweed in clumps so that monarch caterpillars can crawl between them to forage.
• Plant with an eye for multi-season blooms of native plants so that monarch butterflies have nectar sources throughout the growing season!

As of December 2024, the U.S. Fish and Wildlife Service proposed a listing of the North American migratory monarch butterfly as threatened under the Endangered Species Act. Protecting the monarch as a threatened species could be great news for the monarchs! It will provide increased funding, coordination, and focus on the work to save this iconic butterfly species. Read more about this listing and what it means here.

Milkweeds are perennial plants native to the U.S., parts of Canada, Mexico and Central America. They can be found in nearly every habitat from marshes to meadows and even deserts. You’ve probably driven by large stands of milkweed on the side of the road. There are more than 130 species of milkweed, and they vary tremendously in appearance. Some species have large broad leaves while others have small narrow leaves. Some are low growing while others can grow more than 5 feet tall!

Milkweeds are aptly named for the milky, white sap that runs through their stems and leaves. Unfortunately, the other half of its name, “weed,” evokes a wide range of responses from people, including a desire to kill these plants.

By definition, a weed is nothing more than “a plant out of place.”

milkweeds have an important position and role in urban, agricultural and natural areas. They serve as shelter, nesting habitat, and as a food source for a multitude of animal species.

Interestingly, animals that feed directly on milkweed, such as monarch caterpillars, are pretty unique. The white sap these plants produce contain toxic compounds that should kill monarch caterpillars if eaten! But instead, the caterpillars have evolved ways to withstand the toxins and many are able to store them internally to protect themselves from being eaten in the same way the milkweed plant does. Animals that cannot withstand the toxins avoid the plants or eat so little that they are not affected.

Just as monarchs make use of milkweeds and their toxins, humans have utilized these plants for centuries.

Native Americans realized milkweeds could be used to treat a variety of ailments. Externally, sap was used to remove warts and relieve symptoms of poison ivy. By boiling the plant, they found ways to remove milkweed toxins in water, using the extracts to suppress coughs, sore throats, and to treat typhus fever and kidney disorders. After several rounds of boiling, stems, buds and immature pods could then be eaten.

Some of the most impressive uses of milkweed come from the white fluff (floss) inside of pods which was used to stuff pillows, mattresses and blankets. In our modern era, the insulative and water-repelling properties of the fluff have been discovered and used in many ways. In World War II, the buoyancy of milkweed fluff was put to the test when it was used in military life jackets instead of kapok. In addition, the fluff has excellent oil absorbing properties and can be used to soak up spilt crude oil while repelling water. The fluff has also been used as insulation in jackets worn by climbers ascending Mount Everest.

For as long as milkweed plants have been around, they have been crucial to the survival of a variety of animals, including hundreds of insect species that use the plant for food or shelter. Their flowers are visited by many species of native bees, wasps, and other nectar-seeking insects. Their leaves and roots are food for numerous beetles, caterpillars and true bugs. Insects feeding on plants serve as food for predators and parasitoids, which promotes ecosystem stability and species diversity.

Insects in these milkweed communities also serve as a critical food source for a number of birds, such as pheasants and quail.

Insects are a critical part of every food web but due to habitat loss and a lack of nectar or other food sources, many species are in decline. Pollinators, especially native bees, have lost food and shelter across the U.S. and have declined at an alarming rate. Planting milkweed (this summer Pheasants Forever and Quail Forever will surpass a billion seeds in the ground since seed program inception) can help to establish an entire food web, not only supporting monarch butterflies but also contributing to the survival of countless other insects and birds – including pheasants and quail and upland songbirds.

Monarch larvae are specialist herbivores of plants in the family Asclepiadaceae (milkweeds), and have been recorded feeding on 27 different North American species in this family (Malcolm and Brower 1989). The larvae sequester toxic steroids, known as cardenolides, from milkweed (Brower 1969; Brower & Glazier 1975; Malcolm 1991, 1995), and they use these cardenolides as a defense against predators. The bad taste and toxicity of both the larvae and adults are advertised by conspicuous, warning coloration. When a bird or other predator tastes a monarch, it learns to associate this color pattern with the bad taste and avoids preying on monarchs in the future.

Early in the 20th century, Poulton (1909) suggested that the reason monarchs feed only on milkweeds might be because chemicals in the milkweeds provide them with some protection from predators. However, it was not until the 1960’s that researchers discovered that cardenolides were the chemicals in milkweed that made monarchs toxic and bitter-tasting (Parsons 1965). Since then, several studies have shown that monarchs are able to sequester these toxic compounds. For example, Figure 1, drawn from data collected by Malcolm and Brower (1989) shows the range of cardenolide concentrations found in one species of milkweed, Asclepias viridis (Green Antelopehorns), and adult monarchs that fed on that milkweed as larvae. Since the adults do not eat milkweed, this shows that they have stored the cardenolides that they ingested as larvae.

Frequency distribution of cardenolide concentrations in A. viridis (collected in Louisiana) and monarch butterflies fed this species. This shows that monarchs are able to store cardenolides that they ingest as larvae.

The cardenolides obtained from milkweed make monarchs toxic to many vertebrate predators (e.g. Brower et al. 1974, Rothschild et al. 1975). For example, captive bluejays fed monarchs containing cardenolides throw up after eating the monarchs, and the probability of their throwing up increases with increasing cardenolide concentration in the monarch (e.g. Brower 1969, Brower et al. 1972, Brower and Glazier 1975). Other work has shown that wild monarchs containing high levels of cardenolides are also less susceptible to natural predation by both birds (Fink and Brower 1981) and mice (Glendinning et al. 1988).

Protection from vertebrate predators is probably most important to later larval instars, pupae, and adults, whereas earlier instars are more likely to be eaten by arthropods such as mites, spiders, ants, wasps and bugs. Vertebrates tend to be long-lived and able to use learning to avoid noxious foods, and most people agree that the bright colors found on monarchs and other toxic insects help to identify them to vertebrate predators that have learned to associate these colors with bad tastes (e.g. Turner 1984). However, it is not clear that invertebrate predators learn to associate bright colors with bad taste, or even that monarchs are toxic to invertebrate predators.The lack of knowledge on the relationship between milkweed, monarchs, and invertebrate predators represents an important gap in our knowledge.

Based on reported MLMP data, most mortality of monarchs probably occurs in the early instars. As alluded to above, a portion of this mortality is due to invertebrate predation. Chrysoperla rufilabris (Green Lacewing) larvae is a common inhabitant of milkweed species and a voracious predator of monarch eggs. A 2007 Monarch Lab study determined that C. rufilabris larvae depleted 35 eggs from milkweed in 24 hours, seemingly unaffected by the monarch’s toxicity. Results of this study demonstrate the susceptibility of monarchs to predation by invertebrates and provide valuable information for future studies of invertebrate predation and cardenolide sensitivity (Monarchs in a Changing World: Biology and Conservation of an Iconic Insect).

Milkweeds, ranging from the widely recognized Common Milkweed (Asclepias syriaca) to the versatile Butterfly Weed (Asclepias tuberosa) and the showy Swamp Milkweed (Asclepias incarnata), are perennials native to North America. They stand out with their sturdy stems, distinctive leaves, and clustered flowers. Their nectar is a sweet treat that’s irresistible to many pollinators, and the sweet, vanilla scent on a still summer evening is remarkable.

There are 73 species of native milkweeds in the United States, many of which are rare, threatened, or endangered. Monarch butterflies utilize about 30 of these species as host plants, so you do have choices beyond the Common Milkweed, which can be a challenging variety in a typical home garden.

Milkweed’s importance is deeply tied to its relationship with the incredible Monarch butterfly. The butterfly’s lifecycle is unique and fascinating, and milkweed plays an integral role. Monarch caterpillars depend exclusively on milkweed plants for nourishment and shelter. It’s simple – without milkweed, there would be no Monarchs.

This lifecycle begins when monarch butterflies lay their eggs solely on milkweed plants, including Common milkweed, Swamp milkweed, and Butterfly weed (please do NOT confuse this with the non-native, invasive Butterfly Bush).

After hatching, the caterpillars feed on the milkweed leaves, storing the plant’s toxins, which deter potential predators. These caterpillars then transform into the spectacular monarch butterflies known for their extraordinary migratory journey spanning thousands of miles from Canada and the United States to Mexico.

The survival of these migratory wonders is deeply linked to the availability of milkweed along their migration route. Monarchs depend on these plants to lay eggs, thus fostering the growth of the next generation of butterflies.

More Than Just Monarchs

The relationship between milkweed and monarchs is significant, but milkweed’s role doesn’t stop there. These plants offer valuable habitats for a wide variety of creatures, including a host of insects, birds, and small mammals. Essentially, milkweeds create mini-ecosystems within themselves, providing food, shelter, and breeding grounds for numerous species. I am surprised daily when I visit my milkweed plants. There is always something going on!

Milkweed also plays a role in maintaining the health of our soil and water. As with nearly all native plants, they have an extensive root system that helps prevent soil erosion and enhances soil quality. Acting as natural filters, milkweeds reduce runoff and safeguard water sources from harmful pollutants.

The Threat to Milkweeds and How You Can Help

Despite their immense importance, milkweed populations have fluctuated over the years, with the use of glyphosate and agriculture affecting some of the populations. However, there is some research that indicates milkweed is not experiencing a significant decline. Factors such as habitat loss, pesticide use, and land development threaten these vital plants, leading to effects on Monarch butterfly populations since is their sole host plant.

As scientists research these fluctuations and debate whether or not the monarch should be listed as an endangered species or not, I am going to simply recommend you plant milkweeds because they are fascinating plants, they do host Monarch caterpillars, and they are continually alive with action. And, the common milkweed smells so good you won’t believe it.

But there’s hope. We all can contribute to the conservation of milkweeds and, consequently, the rich biodiversity they support. Planting various types of milkweed in our gardens, parks, and public spaces can help provide the critical habitats these plants offer to a range of pollinators and other wildlife.

I encourage you to ask for native plants at your local nurseries and to purchase plants from local native plant vendors. There is a milkweed ideal for planting on some part of your property. Common Milkweed isn’t ideal for smaller, or more formal garden settings, but you may find the amazing Butterfly Weed a great option.

Just keep in mind, Monarchs require more than milkweed! They do require them as host plants for their caterpillars, but they need a variety of native plants blooming at different times of the year to fuel their efforts and their long journey. Consider goldenrods, asters, coneflowers and much more. Please reference the detailed list from the Xerces Society on their website for Monarch nectar plants. They even have a Milkweed Finder!

The monarch butterfly species, Danaus plexippus, has existed for an estimated one million years. Long before that, the monarch’s ancestors had similar traits that would allow for long-distance flight, suggesting that butterfly migration is even older than the monarchs themselves. It wasn’t until 20,000 years ago, however, that monarchs dispersed from their origin in North America to Central America, South America, and the Caribbean. After the peak of the last ice age, receding glaciers and a warmer climate allowed milkweed to colonize new areas. The monarch butterfly followed milkweed around the world, and its range now includes the North Atlantic coast of Africa, Europe, and the South Pacific.

Milkweed is the common name for many plants in the genus Asclepias. It is an herbaceous perennial, recognizable by its broad opposite leaves, colorful flower clusters, or seed pods filled with silk that carries its wind-dispersed seeds. Monarch butterflies only lay eggs on milkweed and monarch caterpillars only feed on milkweed leaves. The key to this specialized relationship is found in the milky latex produced by the plant, which contains compounds called cardiac glycosides that are poisonous to most other animals. The monarch butterfly has developed resistance to this toxin, giving caterpillars a strong chemical defense against predators. In response, milkweed is trending toward faster regrowth following monarch caterpillar activity rather than increased toxicity. This is an example of coevolution, the process of living things influencing one another over thousands or millions of years.

The monarch gets all the press, but queen and soldier butterflies also use these native milkweeds as larval host plants for their caterpillars. Many other butterflies (pipevine, spicebush and eastern swallowtail) and bees, (native sweat bees, leafcutter bees and yellow-faced bees) rely on these starry little flowers for pollen and nectar.

• OE (Ophryocystis elektroscirrha) is a protozoan parasite that begins its life cycle as inactive spores on plants waiting to be eaten by a larva. Once consumed, it multiples within the larva and produces new spores on the butterfly’s scales when it emerges. When the levels of OE multiply and get too high, it impacts the fitness and survivability of the butterfly.
• Warming temperatures, loss of habitat, and the prevalence of non-native tropical milkweed, Asclepias curassavica, contribute to heavier OE loads, increase in OE infection, OE transmission and local population loss.

My hope is that we won’t forget that the importance of milkweeds extends far beyond monarch butterflies. There is an excellent field guide funded by the National Science Foundation titled Milkweed, Monarchs and More: a field guide to the invertebrate community in the milkweed patch written by Ba Rea, Karen Oberhauser and Michael A. Quinn and published in 2003. If you don’t have it, you want it!

The Primrose Milkweed (A. oenotheroides) is more common elsewhere in the state where it flowers throughout the year, but the Panhandle boasts its own stand in Palo Duro Canyon State Park. This milkweed is a prime example that milkweeds serve more than just monarchs. The Queen (Danus gilippus), one of the beautiful but less famous “milkweed butterflies,” also benefits from our milkweed work.

There are other milkweeds from the Texas Panhandle that you may find interesting. The Plains Milkweed (A. pumila) is quite small and easily overlooked among the short-grass prairie unless it’s in flower (June-September) or in fruit. It occurs on sandy and caliche soils and is most often found in groups, which helps to make its presence noticed.

Showy Milkweed (A. speciosa) is stunningly eye-grabbing when in bloom May-September, and even more so when you stumble onto a cluster. This may be a species you have already introduced into your own gardens.

Monarchs are the poster child for milkweeds. However a diversity of native plants and their communities sustain these magical creatures that have captured our imagination. The passion for growing natives – championed decades ago by Carroll Abbott and his “Grow good!” philosophy – is in the midst of a resurgence. Who would have thought that a 6-legged beauty would inspire such action? Carroll Abbott, for one, would be pleased.