Microhabitats of the Metroparks: Milkweed

8.19.2026 Microhabitats of the Metroparks: Milkweed

By Erin Parker, Interpretive Services Supervisor

August is peak time for Michigan’s pollinators and their associated host plants. Monarch butterflies seem to be everywhere as they search for milkweed. And if you come across milkweed patches, you’ll likely find the leaves covered with holes, bite marks, and a wide variety of insects, arachnids (spiders and their relatives), and even mollusks (snails and slugs). It turns out that a close look at milkweed shows a busy, thriving, and diverse community of organisms.

Monarchs and milkweed

Michigan is home to about 12 species of milkweed, though there are over 100 species worldwide. True milkweeds belong to the Asclepias genus named for the Greek god of healing, Asclepius. The characteristics of milkweeds include a thick sap, leaves that grow opposite each other or in whorls around the stem, and a seed pod that splits open when ripe to release fluffy, wind-carried seeds. And parts of most milkweed plants are toxic to most animals, including people.

Monarchs are among the few animals that regularly consume milkweed and even utilize the toxic properties of the sap to their advantage. Milkweed plants are the only host plants for monarch caterpillars, which means that female monarchs lay their eggs only on milkweed, and when the caterpillars hatch out, they only eat milkweed leaves. Because the caterpillars are voracious eaters- think Eric Carlson’s The Very Hungry Caterpillar, but instead of pears and cheese and chocolate cake, monarch caterpillars just eat leaves and flower buds! Because of the rapid growth of monarch caterpillars and the need for a great deal of food in the form of milkweed plants, female monarchs only lay a single egg at a time, on the underside of a milkweed leaf. They then move on to another plant, laying 300-500 eggs in a few short weeks.

Just a few days after the egg is laid, it hatches out, and the caterpillar eats the remains of its eggshell and then begins eating milkweed leaves and buds. The brightly striped caterpillars will go through a cycle of eating, growing, shedding their skin, eating their shed skin, and eating more leaves 4 more times over roughly 8-15 days. Cooler temperatures slow the process down, and warmer temperatures encourage more rapid growth. The final stage of the monarch life cycle takes place away from milkweed. The largest caterpillars crawl away to find a protected place to create their chrysalis. They’ll remain in the chrysalis for up to two weeks, so this part of the metamorphosis takes as long as all the other stages combined! Finally, the adult ecloses (emerges) and feeds on the nectar of a wide variety of flowering plants.

As the caterpillars consume the leaves and buds, they begin storing plant chemicals in their tissues. The more they eat and the bigger they grow, the more chemicals they store. This makes them both toxic and bad-tasting, so potential predators quickly learn to avoid both the large caterpillars and adult butterflies.

Milkweed as a microhabitat

While monarchs may be the most well-known milkweed inhabitant, there is a whole community of organisms that rely on milkweed plants for food. Young caterpillars and eggs, especially, are favored prey for a variety of organisms. Even as they reach their final stages (called instars), many organisms use them despite their bad taste and toxic buildup.

Two groups of insects, parasitoid wasps and flies, lay their eggs on the large caterpillars, essentially turning them into living food for the young wasps and flies. This is a good strategy, as the largest caterpillars are unpleasant enough to predators that they won’t be eaten, and the developing flies and wasps have a protected food source and shelter.

Several species of beetles live on milkweed plants specifically, eating leaves, seeds, roots, and sometimes eating monarch eggs and caterpillars along the way. None of these cause permanent harm to milkweed plants, which are perennial and return year after year. And incidental consumption of eggs and early-stage caterpillars by these omnivorous insects is unlikely to harm monarchs at the population level – it is estimated that only about 5% of monarch eggs laid each year produce adult monarchs!

A variety of other organisms, including spiders, ants, earwigs, and ladybugs, are actively seeking prey among the leaves and flowers of the milkweed plants. While they may eat monarch eggs and young, they are more likely to consume pollinators that are attracted to milkweed flowers and other, smaller predators.

There is even another species of caterpillar that uses milkweed. The milkweed tussock moth has groups of fuzzy caterpillars on the leaves and also becomes poisonous and unpleasant-tasting to predators. They are voracious eaters of milkweed leaves, like monarch caterpillars, but also a natural and important part of the milkweed ecosystem!

Attracting and supporting monarchs and growing milkweed

The first step to encouraging monarchs and the rest of the milkweed community is to have milkweed! Common, swamp, and butterfly milkweed are commonly found at native plant sales and through seed companies. The second step may be to cut back about 1/3 of your milkweed patch in June to encourage fresh new growth as monarchs are arriving in Michigan. Female monarchs seem to prefer young leaves and stems for egg-laying, and this may be because younger plants have fewer potential threats to the eggs and caterpillars. Cutting the plants back later in the season typically doesn’t result in as much young growth in part because our hot summers may not provide the moisture that the plants need to start new growth.

Keep an eye out as you’re exploring your Metroparks; this is a great time to observe the interesting community of organisms that call milkweed home!