Red Milkweed Beetle - Tetraopes tetrophthalmus - Ben Caruthers
Everywhere you come across the word milkweed in the press it is tied to Monarchs. The butterflies’ populations are down from loss of milkweed because of extensive roadside mowing, herbicide use and monoculture farming in rural areas. This has led to a major effort to grow milkweed in parks, other public spaces and even our yards. It turns out that this isn’t the first time that Americans have been encouraged to grow milkweed.
There was an earlier program during World War II to plant and harvest milkweed. The seed pods were collected and shipped to central collection stations. Milkweed floss is over 5 times as buoyant as cork and a lightweight life jacket was both effective and easy to store. It was also warmer than wool and 6 times lighter, perfect for aviators flying over the ocean.
Because milkweed is best known for being the obligatory host plant for Monarch caterpillars it is easy to forget about the value of milkweed in nature. There are several species native to Missouri. Common milkweed (Asclepias syriaca) grows in the easter 2/3rd of the United States. To the 450 species of insects that feed on it, it must look like Walmart.
In our back yard a lot of other insects can be found on the plants. The Large Milkweed Bug, Oncopeltus fasciatus, has orange stripes. This bright aposematic color advertises its accumulation of toxic chemicals from the plants and say “don’t even think about eating me!” As true bugs (Hemiptera) they go through 5 juvenile life stages, all resembling smaller versions of the adult.
Milkweed Tussock Moth caterpillars also collect toxins as they chew away on the leaves. You would think that predators would look at all those hairs and say “yuck!” The adult moth also makes ultrasonic clicks to warn bats and others to stay away.
The Southern Milkweed Leaf Beetles, Labidomera clivicollis, are again brightly colored and pick up toxin, but they believe in moderation. They will cut the vein of the leaf to drain out some of the sticky milky sap before chewing the leaf.
Milkweed Aphids, Aphis nerii, feed on the sap and get a little chemical protection. They can push noxious secretions out their little tailpipes called cornicles. Scientific studies have shown that when this secretion is applied to a spider's mouth parts, it will retreat and wipe its mouth (and presumably make a terrible face!) This shows that the secretion is an effective deterrent. It also suggests that some entomologists have way too much time on their hands.
Looking at the ant above you might think these aphids are toast but they actually have a more interesting relationship. The aphids suck sugary phloem from the plant and excrete excess sugary secretions which may collect on the plant. Ants get this nutritious drink from the aphids and it protects them. In return the ants tend the aphids almost like a farmer with dairy cattle.
Meanwhile back to the butterfly. Monarchs spend the winter in Mexico, then fly north to the southwestern states where they mate, lay their eggs on milkweeds and die. Their caterpillars munch, grow, shed their skin 5 times then form a chrysalis and emerge to fly north. They do this through three generations, each time settling down where milkweeds are in season.
Then a miracle occurs and the last migratory generation flies back to the Mexican forests which their great-grandparents migrated from last spring! They will live there for up to 9 months before starting the cycle again. How they find that wintering spot without a GPS, no one knows.
More on common milkweed, Asclepias syriaca, is here.