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The Dangers of Non-Native Milkweed for Monarchs


monarch caterpillar on tropical milkweed

With the rapidly declining populations of monarch butterflies, more and more people are planting milkweeds to support them.


But due to the rise in demand for these vital plants, garden centers are selling any milkweed species they can get ahold of.


Not all milkweeds are created equal, though. Non-native milkweeds, like tropical milkweed, can harm monarch butterflies.


This article will cover the dangers of non-native milkweeds, including which species to avoid.


If you want to truly support monarch butterflies, it's imperative to only plant native milkweeds.


Let's get started.


Why Non-Native Milkweeds Are Bad for Monarchs


1. Disruption of Migration Behavior


The first issue with non-native milkweeds is that they can disrupt monarch migration behavior.


Every spring, monarch butterflies migrate to North America for their breeding season. During this time, milkweeds are the sole host plants used to lay eggs on, helping create the next generation of monarch butterflies.


monarch butterfly migration map

This new generation of monarchs migrates south to overwinter in Mexico when fall arrives.


While on this journey, non-native milkweeds can trick them into another breeding season, causing them to delay or even stop their migration to Mexico.


The cold winters of North America will kill the monarchs if they don't make it out in time.



2. Disease Concerns


The second issue with non-native milkweeds is that they can increase disease in monarchs.


OE (Ophryocystis elektroscirrha) is a parasite that deforms monarch butterfly wings, significantly affecting their migration ability.


When an infected monarch lays its eggs, it could deposit the parasite's spores, spreading the infection to its eggs and the milkweed plant.


monarch butterfly with OE infection
Monarch butterfly with OE infection. Photo by Judy Gallagher (CC BY 2.0)

Non-native milkweeds have unnaturally extended growing seasons, creating a longer period for the parasite to spread to new monarchs.


As more eastern monarchs become infected, fewer can complete their journey south due to wing deformations.


If the infection is bad enough, they can even die in the chrysalis stage.

 

For more information on the effects of non-native milkweeds, please visit the Xerces Society.



Milkweeds to Avoid


1. Tropical Milkweed


Tropical Milkweed (Asclepias curassavica) is the most common non-native milkweed for sale. It originates from Central and South America.


Cultivars of varying colors have been bred for the garden industry, but all have the same scientific name.


Here are some of the cultivars you might find at a garden center:


Red Tropical Milkweed


Red Tropical Milkweed

Red Tropical Milkweed (Asclepias curassavica) is the most common color variation. Its distinctive combination of red and yellow makes it easy to avoid.



Orange Tropical Milkweed


Orange Tropical Milkweed

Orange Tropical Milkweed (Asclepias curassavica) could easily be mistaken for our native Butterfly Milkweed (Asclepias tuberosa). It's a prime example of why checking scientific names is essential when selecting plants.



Yellow Tropical Milkweed


Yellow Tropical Milkweed

Yellow Tropical Milkweed (Asclepias curassavica) was bred to be pure yellow, making it a relatively easy color to discern from natives.

 

There are multiple other cultivars of tropical milkweed, but they are all color variations of the three shown above.



2. Balloon Milkweed


Balloon Milkweed (Gomphocarpus physocarpus) is another non-native milkweed you might find at a garden center. It originates from Southeast Africa.


While not as studied as tropical milkweed, as a non-native, it could also cause issues for the monarch's natural life cycle.


It's best to avoid this species as well to be safe.


balloon milkweed flowers

The feature that sets balloon milkweed apart is its yellowish, ball-like fruits, which give it its common name.


balloon milkweed fruit


Conclusion


The rapidly declining populations of monarch butterflies call for immediate action to support their survival.


While the increasing demand for milkweeds is encouraging, it's crucial to recognize the dangers posed by the non-native species found at garden centers.


To truly make a positive impact and support monarch butterflies, it's imperative to only plant native milkweed species.


By doing so, we can create safe and sustainable habitats for monarchs, ensuring their continued existence for future generations.

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