Milkweed. It’s not just for the monarchs.

Post by Jen Berlinghof

Being home more these past months has allowed my family copious time to observe the common milkweed (Asclepias syriaca) in our garden go through its life cycle day by day. We’ve witnessed the transformation from wily little sprouts in early summer to blooming beasts, with pompoms of eraser-pink flowers wafting perfume across the yard—even threatening to take over the footpath—by Fourth of July. Now in the sweet days of September, our milkweed is laden with swelling seed pods, ready to burst with floating seeds like so many little white parachutes scattered in the autumnal sky. The situation is similar in many of the Lake County Forest Preserves in northern Illinois.

The beautiful flowerhead of common milkweed (Asclepias syriaca). Photo © Lake County Forest Preserves.
The beautiful flowerhead of common milkweed (Asclepias syriaca). Photo © Lake County Forest Preserves.

Along with daily observations of the flora come the fun and excitement of watching the fauna that use our little plot. Like witnessing each stage of the milkweed’s growth, we’ve observed each stage of the monarch butterflies’ (Danaus plexippus) metamorphosis as well. My youngest son seems best at spotting the teeny, striated eggs on the undersides of leaves—he does have the youngest eyes, after all.

We spent one afternoon watching a plump monarch caterpillar devour a leaf, leaving only a pile of frass behind. One morning at dawn, we found the treasure of a frosty-green-and-gold, bejeweled chrysalis hidden in the patch. And we’ve spent countless summer evenings gazing at monarch adults as they floated back and forth through the garden, sipping the sweet nectar of the milkweed flowers in their own happy hour.

The monarch butterfly (Danaus plexippus), while iconic, isn't the only species that uses milkweed. Stock photo.
The monarch butterfly (Danaus plexippus), while iconic, isn’t the only species that uses milkweed. Stock photo.

While monarch butterflies are the best-known milkweed loyalists, there are other similarly orange-and-black insects that we observed using this important native plant. These insects are part of a club known as the Monarch Mimicry Complex. Membership entails feeding on toxic milkweed and wearing the same warning colors as monarchs, giving them protection from predators in return.

All of these milkweed specialists have evolved, in one way or another, to deal with the milky sap of the plant. It contains cardiac glycosides, which can be poisonous in large quantities. They even use the treat of toxicity to their own defense, advertising that they’re unpalatable and even dangerous to consume with their vibrant orange and black patterns. These act like a big, flashing danger sign to would-be pursuers.

This milkweed tussock moth caterpillar (Euchaetes egle) is quite noticeable against its milkweed host. Photo © Allison Frederick.
This milkweed tussock moth caterpillar (Euchaetes egle) clings to its milkweed host. Photo © Allison Frederick.
Milkweed tussock moth larva can skeletonize milkweed leaves. Photo © Allison Frederick.
Milkweed tussock moth larva can skeletonize milkweed leaves. Photo © Allison Frederick.

The milkweed tussock moth (Euchaetes egle) has voracious larva that skeletonize milkweed leaves in the blink of an eye. The species retains toxins from the sap like its fellow lepidopteran, the monarch. While monarch larva feed on young, fresh shoots, the tussocks seem to favor older shoots, so there’s rarely competition between the two.

The adult moth is a lackluster brown, yet the larvae is a showstopper. It sports long tufts of orange, black, and white hairs, warning daytime predators to stay clear and find some other food that won’t possibly make them vomit. But since the adult moths are nocturnal, they don’t really need the warning colors to evade their bat predators, who hunt using sound rather than sight. Instead, the milkweed tussock moth has developed an auditory warning in the form of ultrasonic clicks that bats have come to associate with a foul meal.

Large milkweed bugs (Oncopeltus fasciatus) feast on milkweed seed pods. Stock photo.
Large milkweed bugs (Oncopeltus fasciatus) feast on milkweed seed pods. Stock photo.
A small milkweed bug (Lygaeus kalmii) rests on a milkweed flowerhead. Stock photo.

Next up in the milkweed mimicry club are the milkweed bugs (Oncopeltus fasciatus and Lygaeus kalmii). These seed-specializing hemiptera, or true bugs, also store those damaging cardiac glycosides by consuming milkweed. In early fall, they congregate in large numbers on milkweed pods. They use straw-like mouthparts to inject enzymes into seeds, liquifying the plant food so they can suck it back up for a savory seed shake. The pokey proboscis only reaches so far. While they do devour the outer seeds, many inner seeds stay intact.

The large milkweed bug (Oncopeltus fasciatus), which is 0.75 inches long with a wide, black band across the center of its orange-and-black body, is migratory like the monarch. Its movements follow that of flowering milkweed. The small milkweed bug (Lygaeus kalmii) is only a half-inch long, sports a large red X on its back, and overwinters as an adult in the detritus of fields and gardens.

A milkweed beetle (Tetraopes tetrophthalmus) traverses a milkweed leaf. Photo © Allison Frederick.
A milkweed beetle (Tetraopes tetrophthalmus) traverses a milkweed leaf. Photo © Allison Frederick.
The black polka dots of the milkweed beetle (Tetraopes tetrophthalmus) are easily recognizable. Stock photo.
The black polka dots of the milkweed beetle (Tetraopes tetrophthalmus) are easily recognizable. Stock photo.

The last in the mimicry club we saw this year is the milkweed beetle (Tetraopes tetrophthalmus), whose orange-red and black polka-dotted body continues the aposematic tradition. Members of the order Coleoptera, these long-horned beetles have chewing mouthparts. They’re great for severing the large leaf veins of milkweed, which reduces the flow of milky sap that can gum up their chompers while they feast on the drained areas of said leaf.

Milkweed is not just food for these guys. It’s home as well. Milkweed beetles lay their eggs in milkweed stems near the ground. Once hatched, larva tunnel into the roots to feed during early fall before nodding off to overwinter in the rhizomes beneath the soil.

Purple milkweed (Asclepias purparescens) at Middlefork Savanna in Lake Forest. Photo © Lake County Forest Preserves.
Purple milkweed (Asclepias purparescens) at Middlefork Savanna in Lake Forest. Photo © Lake County Forest Preserves.

Since we’ll all probably spend even more time in our backyards and gardens this fall, it’s a good time to go investigate your own milkweed. See who’s sipping, slurping, chewing, and living on this significant native plant. Early autumn is also a good time to consider planting natives in your garden. There are many species of milkweed native to northern Illinois. This Chicago Botanic Garden guide will help you determine which ones might be best for your yard. You can also join us for a FREE virtual Native Plant Landscaping program on September 24, 7-8 pm to learn more about how to bring native plants into your garden.

3 thoughts on “Milkweed. It’s not just for the monarchs.

  1. I planted common milkweed a few years ago. The first two years I had lots of caterpillars. I did notice their eggs. Never saw a chrysalis. Saw lots of butterflies. One year I brought them in and raised them until I learned that indoor raising causes them to lose their migration sense.
    The last three years I have had lots and lots of milkweed, but no caterpillars. We have also had numerous insects you discuss.
    Am wondering why we no longer attract monarchs.

    • Thanks for reading Ellen! If it’s monarch season and you’re not seeing monarchs at your site, there are a few things that could be happening. Monarch larvae have natural predators, such as ants, spiders, and wasps, that may be getting them before you can spot them. There are even monarch parasites such as the tachnid fly Lespesia archippivora which attacks larvae. If disappearing caterpillars are 5th instar caterpillars, odds are they moved away from your milkweeds to find a safe place to form their chrysalis (they typically do not pupate on milkweed plants). If earlier instars or eggs are disappearing, a more likely culprit is a monarch predator. Researchers have discovered that less than 10% (with some studies as low as 2%) of monarch eggs actually reach adulthood. While of course milkweed is of utmost importance,make sure to include a variety of native flowering species with different bloom times to provide monarchs with the food they need to reproduce in the spring and summer and to migrate in the fall. Offering a wide array of native nectar plants will attract monarchs and many other butterflies and pollinators to your habitat all season long. Additionally, insecticides should never be used in or surrounding pollinator habitat. Limit use of herbicides within and surrounding the habitat only to control invasive or noxious weeds. While you might not be using insecticides or herbicides, you might want to ask (politely) neighbors. I found this to be the case a few years ago, a neighbor was spraying insecticide before having backyard parties, and it was drifting into my yard.

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