Whereiwander… A patch of common milkweed (Asclepias syriaca) can be a fascinating place for observation and discoveries. We have several patches in our three and half acre meadow, each plant providing an array of food from the leaves, stem, seeds and roots. There are a hundreds of insects and arachnids (spiders) that depend on this plant. Milkweed is a native plant and its blossoms are very fragrant. It can grow in meadows, gardens, country roadsides and most undisturbed parcels of land. In addition to common milkweed there are 109 other species that grow in North America. Another species which is quite often seen in the Adirondacks is swamp milkweed (Asclepias incarnate), which prefers wet feet. I have found it growing along the Moose River and it can be seen while kayaking or canoeing. It is generally taller than common milkweed and the blossoms are smaller and a darker pink. The seed pods of the swamp milkweed are smaller too. The botanical name for a pod is follicle.
Some of those that depend on milkweed as a food source are herbivores feeding on its leaves, stems and roots. Some are nectivores feeding on the plants’ nectar, others are predators that use the plant as hunting grounds to find and eat others insects which frequent milkweed. And there are even some that are parasites and will lay their egg or eggs on the larvae of other insects, and there are also decomposers and others scavengers, each depending on the milkweed plant.
Perhaps you already know, milkweed is the host plant, for the monarch butterfly (Danaus plexippus). A host plant is the plant on which the butterfly, or other insect, lays its egg and the larva feed upon it. Some butterflies have multiple host plants, but milkweed (Asclepias) is the only host plant for the monarch butterfly; however she uses all of the different species of milkweed. As the female approaches a milkweed plant she will smell it with her feet, the lower part of her leg is called a tarsus, which is where the smell receptors are located. Each egg is minute and she usually attaches it to the underside of the leaf. With a magnifying glass or a loop you can see that the egg has ridges and a conical shape. When days are warm the egg may hatch within four to six days. The newly hatched larva (caterpillar) will eat the egg case first and then begin to eat the milkweed leaf. Then it becomes an eating machine, eating and growing continually for two to three weeks. As is eats it sheds its skin, just like we do when we outgrow clothes. This will occur at least five times and each new molt is called an instar. After the fifth instar the larva is now about two inches in length. It has yellow, black and white stripes and two long tentacles in front and two shorter tentacles in the back.
The caterpillar may use the host plant, but quite often will crawl to another place close by and spin a “silk button” which it attaches to itself, and to a stem or twig. It will hang from the silk button for several hours or perhaps even a day. The final molt is quite miraculous to observe, when the larva sheds that last skin the pupa (chrysalis) is revealed. The pupa begins to shrink and harden into a pale green capsule which is ringed with a golden color ring and golden specks. If you look closely you can even see the adult butterfly within the chrysalis.
In the Adirondacks the final generation of monarch butterflies become adults in mid-August to mid-September, most of these adults will migrate to overwintering sites.
Milkweed has many benefits to insects which eat it; the main one is that the insects become toxic to many predators. While eating the leaves, stems and roots the insects absorb a toxic alkaloid; known as a cardiac glycoside, which may be fatal to birds and mammals. The orange and black color of the monarch lets its predators know “don’t eat me, I am toxic.” The viceroy butterfly is a monarch mimic and although it is not toxic, its coloring (orange and black) warns that it is.
Another insect which depends on milkweed is the tussock moth. The caterpillars of the tussock moth compete with monarch caterpillars for their host food milkweed, but their strategies are quite different.
The monarch butterfly lays one egg per plant while the tussock moth lays as many as fifty eggs in a tight cluster on a milkweed leaf. The tussock caterpillars are communal feeders and all hatch at the same time and begin eating as a group. They eat everything in their path, including any egg or tiny monarch caterpillar, until they have completely skeletonized the leaf, leaving only its veins. As the tussock moth caterpillars go through their instars they develop a black and orange, shaggy dog appearance. This new look also announces that they too are toxic and their shaggy appearance makes them less appetizing.
Numerous beetles utilize the milkweed plant. The milkweed longhorn beetle (Tetraopes femoratus) adult eats the leaves and lays its eggs on milkweed stems, close to the ground. The larvae burrow into the stems and roots and feed, then overwinter underground until spring.
Milkweed bugs, both the large (Oncopeltus fasciatus) and small (Lygaeus kalmia) use milkweed. The large milkweed bug eats the leaves, seeds and nectar. The small milkweed bug prefers the seeds. Ladybug beetles, as many as eight species, can be found on milkweed plants, as well as stink bugs, green lacewings, aphids, cicadas, bees, wasps, grasshoppers, leafhoppers and of course arachnids. Spiders such as orb weaver, crab spiders, jumping spiders and nursery web spiders all visit milkweed patches, in addition to hummingbirds, frogs, snails, me and hopefully you.