The Outside Story

The Outside Story: See what’s in the milkweed patch

By Barbara Mackay

Eight or so years ago I collected milkweed seeds and painstakingly buried them one at a time under leaf debris at the back edge of my yard, hoping they would mature and attract more monarch butterflies to my home. The project has been wildly successful, but recently the monarch population has declined. So far this year I have seen only one.

Still, milkweed is a valuable perennial. Common milkweed (Asclepias syriaca L.) is a sweet haven for a diversity of organisms. Visit a patch along the road or in a field and see for yourself the variety of wildlife that uses this unique wildflower.

As we near the end of summer, you are likely to notice the milkweed tussock moth caterpillar. Its appearance makes it a good candidate for a science fiction movie. It is orangey-brown, with black and white bristles and tufts sticking out in all directions. About one inch long, it often curls into a comma shape on a leaf, and will roll up in a ball if disturbed.

A dozen tussock eggs are laid together, hatch together, and move about as a group, called a colony. They communally devour a leaf, leaving behind droopy, skeletonized, green threads. Surprisingly, a milkweed plant can usually recover from the damage caused by a colony of tussock moth larvae. As they mature, they split up and feed individually.

The red milkweed beetle is a conspicuous milkweed resident. It looks a bit like an elongated ladybug. It has a slim red body with black spots on its back. It sports antennae that seem disproportionately long for its size. If you don’t see the beetle itself, you might see evidence of it having been there: it eats the tapered point of the leaves. It also eats the buds and flowers.

Another insect to discover is the milkweed bug. It has a dark body with an orange X across its back, and a line of orange across where you imagine its neck would be if it had one. Milkweed bugs can live their entire lives, from egg to nymph to adult, on their namesake plant. They are common enough that you might even see a mating pair. You have time: they stay attached (end-to-end) for up to thirty minutes. The milkweed bug has sucking mouth parts and is considered a true bug. It uses its long, straw-like proboscis to inject salivary enzymes into maturing seeds, then sucks out the digested juice. The female lays about thirty eggs a day between seed pods, depositing around 2,000 eggs over a lifetime.

One insect you might see is there to prey upon the other insects. Aptly named, this is the milkweed assassin bug. It can be distinguished from the milkweed bug by its long legs. The assassin bug ambushes its victims with the “sticky trap strategy.” From a hiding spot, it awaits a target with sticky forelegs held high. At just the right moment, it grabs the insect, covering it with a goo from which there is no escape. The assassin bug inserts its beak into its meal, injects digestive enzymes to liquefy the internal tissues, and then sucks up the nourishment.

The milkweed stem weevil is devastating to milkweeds. From early to mid-summer, the female burrows into the plant’s stalk, repeatedly moving up the stem poking holes for her eggs. When the eggs hatch, the newborn larvae eat the surrounding juicy pith. Between a severely weakened stem and the loss of fluids, weevil damage usually results in the death of the whole plant. In late summer, you can see which plants are weevil-damaged: look for black holes along the wilted stem.

How is it that insects aren’t killed when they ingest the poisonous sap, which contains latex alkaloids and cardiac glycosides? In many cases by avoiding the secretion altogether. An initial bite cuts the vein below where the insect wants to eat, which stops the toxic sap from flowing. If you see a milkweed leaf with its end chewed up, you’ll often find that the large veins on the underside have been cut. Other insects can detoxify the poisons internally. One notable insect, the monarch caterpillar, devours the leaf, poisons and all, without any harm.

Many birds, butterflies, bees, wasps, flies, and ants also visit milkweed plants. They are seeking its nectar, which is sweeter and more plentiful than most other wildflowers. Take a close look at a flower. Notice the numerous cup-like parts, called hoods, in groups of five. Each hood holds nectar, worth a sweet taste on your little finger.

To start your own milkweed patch this fall, collect milkweed pods just as they are splitting open, carry them in a tight fist or paper bag, and bury them under leaves or grass so they don’t blow away. Next spring you can enjoy the beauty of the flowers and the bounty of life that depends on milkweed. You’ll be helping out the monarchs, too.

Barbara Mackay is a teacher and naturalist who lives in northern Vermont. The illustration for this column was drawn by Adelaide Tyrol. The Outside Story is assigned and edited by Northern Woodlands magazine and sponsored by the Wellborn Ecology Fund of New Hampshire Charitable Foundation: [email protected].

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