Summer 2018 Conservationist

107 Milkweed Lane

by Scott Kobal, Natural Resources

It’s summer in DuPage, which means talk has returned to milkweeds and monarchs. Milkweeds are the only plants monarch caterpillars will eat, one reason the Forest Preserve District is adding milkweeds to seed mixes and partnering with groups like DuPage Monarch Project to encourage people to put the plants in their own backyards. But far more than monarchs call milkweeds home. 

Eight different kinds of milkweeds grow in DuPage, and nearly every forest preserve is home to at least one type. Their flowers provide nectar for hungry moths, butterflies and bees, and in return the insects move pollen from plant to plant. Without this exchange milkweeds couldn’t reproduce, which would affect residents throughout the milkweed neighborhood. 

Because of its size, one of the most noticeable locals is the milkweed longhorn beetle, a half-inch-long black-spotted red insect with antennae as long as its body. These beetles start off eating the roots and stems of milkweed plants as larvae but move up to leaves and flowers once they’re adults. The similar-looking milkweed bug is equally conspicuous, especially in late summer and early fall, when juveniles and adults cluster together to eat, primarily milkweed seeds. Being “true bugs” they have piercing, sucking mouthparts that punch through the seedpods before pumping in digestive enzymes to soften the contents, which they then siphon out. 

Milkweed leaf beetles, which resemble ladybugs, visit different plants but mostly inhabit swamp and common milkweed, which they aggressively protect. Even if females are not around, males will fight each other to keep the competition away from their home turf. Both larvae and adults prefer not to step in the sticky latex that oozes from damaged milkweed leaves; if it dries it can seal their mouths shut. They cut side veins on the leaves to let the sap drain before they eat and rub against leaves to remove any sap they do encounter. 

Also on Milkweed Lane is the milkweed tussock moth. As small newly hatched larvae, these moths eat milkweed leaves but avoid piercing larger veins that contain the plants’ milk-white sap, which can glue them in place. But as they grow into larger caterpillars (with tufts of fuzzy orange, black and white hairs that make them look like tiny teddy bears) they’ll chew all the way through. 

The oleander aphid is another permanent milkweed resident, although not one originally from these parts. These true bugs get their name from the Mediterranean oleander plant, which carried them by accident across the Atlantic. Scores of these yellow-orange bugs, each about half the size of a grain of rice, can blanket milkweed leaves as they suck out the plant’s juices but are generally harmless. (Besides, efforts to remove the aphids would also remove any monarch eggs and caterpillars, the reason people plant milkweeds in the first place.) 

One thing all of these insects have in common with monarchs is their ability to store milkweeds’ toxic cardiac glycosides in their bodies. The chemicals are harmless to the insects but make them unpalatable to hungry birds and mammals. As a result, all of these insects developed black-and-orange bodies to warn aggressors. 

Because so many insects live and dine on milkweeds, other animals end up on the block as well. Spiders patrol the area for insect meals, and even tree frogs, which often perch on milkweeds’ large flat leaves if they’re in the neighborhood, will grab a winged snack or two. Syrphid flies, ladybird beetles and the larvae of lacewings (aptly known as “aphid lions”) all eat oleander aphids, and ichneumon and other parasitic wasps use aphid bodies as nurseries to feed their young. 

Sugar-loving ants visit milkweeds but not to eat any insects. They’re stopping by instead for the “honeydew,” the droppings oleander aphids leave behind. Some ants go as far as “farming” the aphids, protecting the bugs from hungry larvae and harmful fungi and rubbing their bellies so they’ll excrete more of the sweet liquid. 

Milkweeds offer more than meals, though. In spring Baltimore orioles and yellow warblers use dried milkweed fibers to construct their own neighborhood homes, and American goldfinches pull the soft “floss” attached to each seed to line their nests. (Not to be outdone by nature, one or two companies are using floss from commercially raised milkweeds as a hypoallergenic down alternative for insulated clothing.) 

Yes, milkweeds are essential to the survival of the monarch, but take a closer look and you’ll see how they’re home to so much more.


tree-frog-milkweed-BrettWhaley

Tree frogs don’t intentionally look for milkweeds, but if they find them, the plants’ wide flat leaves make great perches. Image by Brett Whaley/CC BY-NC 2.0