7 Insects Commonly Found on Milkweed

Common milkweed.
Milkweed supports an entire community of insects. Getty Images/David Chapman

When you think of milkweed, you more than likely think of monarch butterflies. In the larval stage of their life cycle, monarch butterflies feed exclusively on milkweed plants, herbaceous perennials in the genus Asclepias. The relationship between monarchs and milkweed is perhaps the best-known example of specialization. As specialized feeders, monarch caterpillars require a specific host plant – milkweeds – on which to feed, and cannot feed on any other plants. Without milkweed, monarchs cannot survive.

The documented decline in the number of monarch butterflies over recent decades has underscored the need to conserve monarch habitat. Conservationists have urged those who care about the monarchs to plant and protect milkweed stands along the monarch migration route in North America. Gardeners, schoolchildren, and butterfly enthusiasts have responded by planting milkweed patches in yards and parks from Mexico to Canada.

If you've taken the time to look for monarch caterpillars on milkweed plants, you've undoubtedly noticed that there are lots of other insects that seem to like milkweeds, too. The milkweed plant actually supports an entire community of insects. In 1976, Dr. Patrick J. Dailey and his colleagues conducted an in-depth survey of the insects associated with a single milkweed stand in Ohio. They documented 457 different insect species, representing eight insect orders, on milkweed plants.

Although you aren't likely to find 457 different insects on your milkweed plot, here's a photographic primer to the most common insects in the milkweed community.

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Large Milkweed Bugs

Large milkweed bugs.
Large milkweed bugs. Getty Images/Glenn Waterman/EyeEm

Onocopeltus fasciatus
Order Hemiptera, Family Lygaeidae

Where there is one large milkweed bug, there are usually more. Immature milkweed bugs can typically be found in clusters, so their presence will catch your eye easily. The adult large milkweed bug ( Onocopeltus fasciatus) is deep orange and black, and has a distinct black band across the back that helps to distinguish it from similar species. It varies in length from 10 to 18 millimeters.

Large milkweed bugs feed mainly on the seeds inside the milkweed pods. Adult milkweed bugs will also occasionally take nectar from milkweed flowers, or suck sap from the milkweed plant. Like the monarch butterfly, large milkweed bugs sequester toxic cardiac glycosides from the milkweed plant. They advertise their toxicity to predators with aposematic coloration.

As with all true bugs, large milkweed bugs undergo incomplete or simple metamorphosis. After mating, large milkweed bug females deposit eggs in crevices between the milkweed seed pods. The eggs develop for about 4 days before the tiny nymphs hatch. The nymphs grow and molt through five instars over the course of about one month. 

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Small Milkweed Bugs

Small milkweed bug.
Small milkweed bug. Wikimedia Commons user Daniel Schwen (CC by SA license)

Lygaeus kalmii
Order Hemiptera, Family Lygaeidae

As you might imagine, the small milkweed bug (Lygaeus kalmii) is similar to its larger cousin in both look and habit. The small milkweed bug or common milkweed bug reaches only 10 to 12 millimeters in length. It shares the orange and black color scheme of the large milkweed bug, but its marking are different. In this species, the orange (or red) bands on the dorsal side form a bold X marking, although the center of the X isn't complete. The small milkweed bug also has a dull red spot on its head.

Adult small milkweed bugs feed on milkweed seeds, and may also take nectar from milkweed flowers. Some observers also report that this species may scavenge or even prey on other insects when milkweed seeds are scarce. 

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Swamp Milkweed Beetle

Swamp milkweed beetle.
Swamp milkweed beetle. Getty Images/Moment Open/Cora Rosenhaft

Labidomera clivicollis
Order Coleoptera, Family Chrysomelidae

The swamp milkweed beetle looks like a ladybug on steroids. Its body is robust and ​rounded, and measures roughly 1 centimeter long. Its legs, pronotum, head, and underside are uniformly black, but its elytra are boldly marked in deep reddish orange and black. But this is no lady beetle. The swamp milkweed beetle is one of the seed and leaf beetles.

Swamp milkweed beetles feed mainly on milkweeds in both the larval and adult stages of their life cycle. They prefer swamp milkweed (Asclepias incarnata), but will readily feed on common milkweed (Asclepias syriaca) as well. Like monarch caterpillars, swamp milkweed beetles take measures to reduce the flow of sticky sap from the host plant. They cut the milkweed veins to let the sap escape before chewing on a leaf.

As do all members of the beetle order, swamp milkweed beetles undergo complete metamorphosis. The mated female deposits her eggs on the underside of the milkweed leaves, to allow newly hatched larvae to begin feeding immediately. The final instar larvae drop to the ground to pupate in the soil.

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Red Milkweed Beetle

Red milkweed beetle.
Red milkweed beetle. Flicker user Katja Schultz (CC license)

Tetraopes tetrophthalmus
Order Coleoptera, Family Cerambycidae

The red milkweed beetle is a longhorn beetle, a group so named for their unusually long antennae. Like the bugs and beetles shown previously, the red milkweed beetle wears the warning colors of red/orange and black.

These animated beetles can be found in milkweed patches from late spring through summer. They prefer common milkweed (Asclepias syriaca), but will settle for other milkweed species or even dogbane in areas where common milkweed isn't so common. Mated females deposit eggs on milkweed stems, near the ground or even below the soil line. Red milkweed beetle larvae develop and overwinter within the roots of the milkweed plants, and pupate in the spring.

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Blue or Cobalt Milkweed Beetle

Blue milkweed beetle.
Blue milkweed beetle. Getty Images/Moment Open/Rundstedt B. Rovillos

Chrysochus cobaltinus
Order Coleoptera, Family Chrysomelidae

The blue milkweed beetle, also known as the cobalt milkweed beetle, is the first milkweed associate in this article that isn't red or orange and black. But don't be fooled, because this milkweed-eating insect sequesters toxins from its host plant, just like monarchs do. The larvae of blue milkweed beetles are known to be obligate root feeders on both milkweed and dogbane.

Female blue milkweed beetles are polyandrous, meaning they mate with multiple partners. In fact, one particular blue milkweed beetle earned an honorable mention in the University of Florida Book of Insect Records for this behavior. She is believed to have mated 60 times!

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Milkweed or Oleander Aphids

Oleander aphids.
Oleander aphids. Getty Images/Photographer's Choice/David McGlynn

Got milkweed? Then you've almost certainly got milkweed aphids, too. These plump, yellow-orange sapsuckers don't specialize on milkweed, but they seem to be skilled at finding it. They're also called oleander aphids, and are actually native to the Mediterranean region, but spread to North America with oleander plants. Milkweed aphids are now well established in the U.S. and Canada.

While aphid infestations aren't good news for plants, they are great news for insect enthusiasts. Once your milkweed attracts aphids, you'll find every manner of aphid eater in your garden: ladybugs, lacewings, damsel bugs, minute pirate bugs, and more. And as the aphids leave behind a trail of sticky, sweet honeydew, you'll see ants, wasps, and other sugar-loving insects as well.

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Milkweed Tussock Moth Caterpillar

Milkweed tussock moth caterpillar.
Milkweed tussock moth caterpillar. Flicker user Katja Schultz (CC license)

Euchaetes egle
Order Lepidoptera, Family Erebidae

How about a caterpillar that looks like a tiny teddy bear? The furry milkweed tussock moth caterpillar is covered in tufts of black, orange, and white. In their first three instars, milkweed tussock moth caterpillars feed gregariously, so you may find entire leaves of milkweed covered in caterpillars. Milkweed tussock moth caterpillars can defoliate an entire stand of milkweed in a matter of days.

The adult moth can occasionally be observed on milkweed (or dogbane), although you might not be impressed enough to notice it. The milkweed tussock moth has mouse gray wings and a yellow abdomen with black spots.