7 Insects Commonly Found on Milkweed

The plant is not just food for monarch butterflies

When you think of milkweed, you 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. Without milkweed, monarchs cannot survive.

The 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 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 looked for monarch caterpillars on milkweed plants, you've probably noticed lots of other insects that seem to like milkweeds. The plant supports an entire community of insects. In 1976, Dr. Patrick J. Dailey and his colleagues conducted a survey of the insects associated with a single milkweed stand in Ohio, documenting 457 insect species representing eight insect orders.

Here's a photographic primer on the most common insects in the milkweed community:

01
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Large Milkweed Bugs

Large milkweed bugs.

Glenn Waterman/EyeEm/Getty Images

Onocopeltus fasciatus (order Hemiptera, family Lygaeidae)

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

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

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

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Small Milkweed Bugs

Small milkweed bug.

Daniel Schwen/Wikimedia Commons/ CC-BY-SA-4.0

Lygaeus kalmii (order Hemiptera, family Lygaeidae)

The small milkweed bug is similar to its larger cousin in look and habit. The small, 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 is different. 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 take nectar from milkweed flowers. Some observers report that this species may scavenge or prey on other insects when milkweed seeds are scarce. 

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Swamp Milkweed Beetle

Swamp milkweed beetle.

Cora Rosenhaft/Moment Open/Getty Images

Labidomera clivicollis (order Coleoptera, family Chrysomelidae)

The swamp milkweed beetle looks like a ladybug on steroids. Its body is robust and ​rounded, measuring 1 centimeter long. Its legs, pronotum (plate covering the thorax), head, and underside are uniformly black, but its elytra (forewings) are boldly marked in deep reddish orange and black. The swamp milkweed beetle is one of the seed and leaf beetles.

In the larval and adult stages of their life cycle, swamp milkweed beetles feed mainly on milkweeds. They prefer swamp milkweed (Asclepias incarnata) but will readily feed on common milkweed (Asclepias syriaca). 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.

Like 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. In the final instar, larvae drop to the ground to pupate in the soil.

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Red Milkweed Beetle

Red beetle standing on milkweed, Indiana, USA
Mike Richart / Getty Images

Tetraopes tetrophthalmus (order Coleoptera, family Cerambycidae)

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

These animated beetles are 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 where common milkweed isn't common. Mated females deposit eggs on milkweed stems, near the ground, or 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 (Cobalt) Milkweed Beetle

Blue milkweed beetle.

Rundstedt B. Rovillos/Moment Open/Getty Images

Chrysochus cobaltinus (order Coleoptera, family Chrysomelidae)

The blue (or cobalt) milkweed beetle isn't red or orange and black, but this milkweed-eating insect sequesters toxins from its host plant like monarchs do. The larvae of blue milkweed beetles are known to be obligate root feeders on milkweed and dogbane.

Female blue milkweed beetles are polyandrous, meaning they mate with multiple partners. One 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 (Oleander) Aphids

Oleander aphids.

David McGlynn/Photographer's Choice/Getty Images

Aphis nerii (order Hemiptera, family Aphididae)

The plump, yellow-orange sapsuckers known as milkweed aphids don't specialize in milkweed but seem to be skilled at finding it. Also called oleander aphids, they are native to the Mediterranean region but spread to North America with oleander plants. Milkweed aphids now are 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. 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
JasonOndreicka / Getty Images

Euchaetes egle (order Lepidoptera, family Erebidae)

The furry milkweed tussock moth caterpillar looks like a tiny teddy bear 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 a stand of milkweed in a matter of days.

The adult moth occasionally is 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.

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