Milkweed and Monarchs

An orange and black butterfly with white spots stands perched on a human finger.
Monarch butterflies are dependent on a plant called milkweed.

NPS Photo / Bryan Maul

Wide pointed oval green leaves point upward with small yellow and white five petal flowers clustered within.
Pictured is a broadleaf milkweed (Asclepias latifolia) in flower.

NPS Photo


Milkweed is an integral part in the monarch butterfly’s (Danaus plexippus) life cycle. Asclepias is the genus for milkweed. Asclepias subverticillata, or horsetail milkweed, and Asclepias asperula, or spider milkweed, are the two most common milkweed plants on the rims of Grand Canyon National Park. Asclepias latifolia, or broadleaf milkweed, is common at lower elevations in Grand Canyon near the river. Monarch butterflies exclusively lay their eggs on milkweed, and milkweed is the only plant monarch caterpillars will use to eat. There are often questions about whether milkweed is toxic or not. The short answer is yes, milkweed sap contains toxins called cardiac glycosides. Milkweed is considered toxic to animals if consumed in large quantities, however most animals tend to stay away from it because of the taste.

This website helps identify some of the most common native species of milkweed and lists the states you can find them in!

An orange and black butterfly with white spots stands on the tops of a cluster of purple flowers.

NPS Photo


Monarch butterflies are an important and unique invertebrate species, spanning across North America. Monarchs inhabit prairies, meadows, grasslands, roadsides, and more. The markings on monarch wings are unique and easily recognized by predators as a warning. Their markings are interpreted by predators similarly to how humans understand a skull and cross-bones sign, signaling poison.

Female monarchs lay their eggs on the underside of milkweed leaves, and once the caterpillars have eaten through their egg, they begin to feed on the toxic plant. Monarch caterpillars go through 5 instar stages before they will chrysalize. The word “instar” is a term for phases between different molting periods for insect larva. The caterpillars will molt into 5 different stages, after they have been eating before they are ready to turn into a butterfly. The chemicals from the milkweed will stay in their bodies as they mature into butterflies. The chemicals act as a deterrent, making the monarchs taste bad to their predators, which then encourages predators to avoid butterflies with these distinct markings on their wings.

Monarchs can be found in parks all over the country!


Fun Fact!

Monarch caterpillars are known to eat 200 times their body weight in milkweed!


Monarch Caterpillar Transformation to a Chrysalis

Two white, black, and yellow striped caterpillars balance on thin green leaves. Two white, black, and yellow striped caterpillars balance on thin green leaves.

Left image
The monarch caterpillar will eat milkweed leaves until it is ready to form a chrysalis.
Credit: NPS Photo

Right image
The monarch butterfly will ultimately emerge from this chrysalis.
Credit: NPS Photo

A black and orange butterfly stands on yellow white flowers amongst skinny green vertical leaves.
A monarch butterfly on a horsetail milkweed (Asclepias suberticillata) flower.

NPS Photo / Melissa Stellar

Lifespan of a Monarch

Monarch butterflies create 4 generations every year. Generations 1-3 generally only live a few weeks, but, just like clockwork, in late summer and early fall there is a new generation born for migration. Generations 1-3 will breed, and lay eggs usually up north but can sometimes move south. The 4th generation monarch is the migratory generation. They are born biologically different in the sense that they will live for 8-9 months and do not mate until the spring when they head up north again. They travel hundreds of miles over several months to make this migration south, towards southern California or Mexico. The migration happens because they cannot survive the cold winter temperatures in the northern states.

Learn more about monarch migration.

Monarchs as an Endangered Species

Monarch butterfly populations have been in a severe decline since the 1980s, when there were over 4.5 million individuals. As of 2019, there were fewer than 30,000 individuals. Some ways that monarchs are being negatively impacted include climate change, milkweed population decline, and winter habitat loss. In 2020 after a lengthy evaluation the United States Fish and Wildlife service (USFWS) declared that listing the monarch butterfly under the endangered species act was warranted but precluded because of other listings that had higher priority. As of now the monarch is not federally protected, in 2024 the USFWS will reevaluate the eligibility of listing the monarchs under the Endangered Species Act of 1973. Most recently in July 2022 the International Union for Conservation of Nature (IUCN) entered the monarch butterfly into the IUCN Red List of Threatened Species as endangered.


Monarchs at Grand Canyon

Grand Canyon National Park and the Colorado River that runs through it occur along a critical monarch butterfly migration path and are the home of host plants that are essential for monarch survival, such as milkweed and other nectar-rich species. Grand Canyon is working to convert degraded land into suitable monarch habitat by establishing pollinator gardens on both rims which include milkweed and nectar-rich plants. If you’re visiting the North Rim, the new pollinator garden is located at the Lodge Cabins adjacent to the Visitor Center and Grand Canyon Lodge. However, if you’re at the South Rim plan on visiting Pima Point, a beautiful stop along Hermit Rd., to check out our newly installed pollinator garden.

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Milkweed is a critical plant for the monarch butterfly life cycle, but monarchs use many different milkweed and nectar-rich plant species throughout Grand Canyon National Park and Dinosaur National Monument. The milkweed and nectar-rich plant species in the parks differ according to region. Milkweed plants are the only ones monarch caterpillars eat, but adult monarchs and other insect species rely on nectar-rich plants in both parks.

A woman in a green hat stands facing a yellow flowered bush with a net overtop of the plant.
A Park Ranger attempts to catch a monarch butterfly out in the field.

NPS Photo

Get Involved!

Scientists at Grand Canyon and across the Southwest also work to safely catch, tag, and document monarchs so that communities across the country can identify monarch migration patterns and learn more about the current population status. Scientists are trained in how to carefully tag monarchs without harming them.

The process of tagging a monarch is a lot harder than most people think because you need to catch the monarch first. Once that is done, you will collect data like the sex, condition, location, and activity of the monarch before placing a small tag on the wing. The tag is a small circle sticker placed on the “discal cell” of the wing which looks like a mitten. We place it there because it allows the monarch to have full movement without it weighing it down.

Make sure to keep an eye out for tagged monarchs not only in the park but across the US, your sightings can help us better understand their migration routes. You can get involved at home by joining community science opportunities in your region! Go to Monarch Joint Venture to find a community science opportunity near you.

By a scenic overlook, a woman is watering an open area with a hose, where native plants are starting to grow.
Watering plants at the Pima Point Pollinator Garden.

NPS Photo

Things You Can Do At Home

It is important to do everything we can to save this species!

Some action items you can take at home are:


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    Last updated: January 24, 2023

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