Asclepius syriaca – Wild Things in the Garden

Part 2

And we’re back for Part II of The Summer Cornucopia! Today the focus is on insects and how they use Common Milkweed. If you missed Part I and are interested in the plant and pollination, here’s a link: https://wordpress.com/post/wildthingsinthe.garden/1831.

Asclepias syriaca draws an abundance of insects. The sap, leaves and flowers are all used for food while blooms provide nectar to many insects. Common Milkweed supports different life stages of flies, wasps, bees, butterflies, moths, skippers, plant bugs and beneficial insects. Even hummingbirds try to sip nectar although they can’t reach it.^1,7

The most famous visitor to Common Milkweed is the Monarch butterfly (Danaus plexippus). Monarchs can only use milkweeds (Asclepias) to feed their caterpillars. Growing milkweed supports the generations of Monarchs that hatch over the summer months. When the last summer generation is born and transforms into an adult, they’ll drink nectar from milkweed and other flowers for food and fuel for their migration.⁸

Growing native milkweeds helps preserve the existing Monarch population. If you’re interested in helping Monarchs, Monarch Watch has excellent information on creating Monarch Waystations at https://www.monarchwatch.org/waystations/ . Here are the highlights of the plan!⁸

How big does a waystation have to be? Any size will help the Monarchs (and other pollinators!). If possible, a 100 square foot waystation is highly effective. The area doesn’t have to be all in one spot. There can be several plantings throughout a property.

Sun is important for Monarchs. Like other insects, they need heat and sunlight to warm themselves for flying and daily activities. An area with six or more hours of sunlight is required. Coincidentally, most milkweeds thrive under those conditions.

Milkweed also grow well in well-drained soil. Place Monarch Waystations in low clay areas with fast draining soils.

Place plants close together (although not closer than recommended). Monarchs and their caterpillars need shelter and protection from predators and the weather.

What about milkweed? At least ten plants are recommended preferably with two or more types of milkweeds. This planting scheme gives an extended season of bloom and allows the Monarchs longer access to the milkweed plants and nectar. One type of milkweed is okay if more than ten plants are included.

Establish continuous supply of nectar plants. Use annual, biennial and perennial plants. Native plants are a great choice. These plants also benefit the other pollinators.

Finally, create a management plan. How will the waystation be maintained? The plan contains basic garden maintenance: mulching, fertilizing, removing invasive plants. Additionally, it includes Monarch specific items: eliminate insecticides, add more features like a water source or puddling spot.

Again, for more information on Monarch Waystations and other resources, including free milkweed programs, go to https://www.monarchwatch.org/waystations/

In addition to Monarchs, swallowtails (Papilio), fritillaries (Speyeria), viceroy butterflies (Limenitis), sulfurs (Pieris), and other butterflies also visit Asclepias syriaca. Skippers use Asclepias syriaca for nectar including Ancyloxipha.^1,7

Common Milkweed is a larval host for the striking Milkweed Tussock Moth (Euchaetes egle) caterpillar, the Unexpected Cycnla (Cycnia inopinates) and the Delicate Cycnia (Cycnia tenera). All are part of the group Artiinae or Tiger Moths.¹

The Delicate Cycnia (Cycnia tenera) lacks the usual aposematic coloration It has a soft tan larva and a charming white adult with just a touch of orange on the head and wing edges. Instead, it emits aposematic ultrasound calls when caught! Bats release their prey when they hear the calls. During the day, their color variation seems to keep birds away.^1,9

Both long-tongued and short-tongued bees visit Common Milkweed for nectar. These include honeybees (Apis),

Bumble Bees (Bombus),

leaf-cutter bees (Megachile),

cuckoo bees (Coelioxys), small carpenter bees (Ceratina)

and sweat bees (Halictus and Lasioglossum).^1,7,10

Many wasps enjoy nectaring at Milkweed flowers especially Sphex, Tachytes, Polistes, Myzinum, and ichneumon wasps. Sphex ichneumoneus is a known pollinator of Common Milkweed.^1,7

Numerous beneficial insects visit Asclepias syriaca including the delicate and diverse ichneumon wasps. The adult wasps use milkweeds’ nectar for fuel while searching for insect prey. They’re considered parasitoids and the females lay eggs inside grubs and caterpillars.

Young of boll weevils, tomato hornworms and wood borers are all food for ichneumon wasps. In addition to garden pests, adults hunt large insects such as spiders and butterflies.

In general, ichneumon wasps help reduce the number of insects that reach reproductive age. Many of these prey insects damage trees. In this way, the wasps help keep trees healthy.¹¹

Bembix americana, a predatory sand wasp, also gathers nectar from Common Milkweed. B. americanafeeds their young true flies (Diptera). Diptera include house flies, gnats and mosquitos.

As populations of flies increase, B. americanas numbers rise. A single larvae can eat two dozen flies. B. americana uses a different strategy for provisioning its young. Other wasps paralyze their prey and stock each cell with the required (living but paralyzed) insects. This sand wasp kills the flies and adds more food as needed.¹²

Asclepias syriaca hosts predatory stink bug larvae. Stink bugs have a terrible reputation especially since the arrival of the invasive Brown Marmorated Stink Bug. But predatory stink bugs are a whole different category. These are beneficial insects that hunt insect prey.

Above, is a photo of a Spined Soldier Bug larvae on milkweed. There are five larval stages (instars) and all eat insects. Their preferred foods include Mexican bean beetle, Colorado potato beetle, and imported cabbageworm.

Look for the adult Spined Soldier Bug on plants where prey may be located. These plants include the melons/squash/cucumber (cucurbit), broccoli, cauliflower, kale, etc. (cruciferous) and tomatoes, peppers, eggplant (solanaceous) crops.

If you’re looking for eggs, they’re an incredible metallic bronze color with a row of spines like a crown. Just hatched larvae, cluster around the eggs eating necessary bacteria. Spined Soldier Bug can be purchased commercially.¹³

In addition to all these, Asclepius syriaca hosts many beetles and bugs,

grasshoppers,

and leafhoppers

Finally, flies, including beneficial ones, nectar on Asclepius syriaca.

I hope you’ve enjoyed this exploration of the insects found on Common Milkweed. Pollinators and beneficials all enjoy Asclepias. It’s always worth stopping to see who’s home in the milkweed patch with or without flowers!

Happy Gardening, Mary

References

Hilty, J., n.d., Common Milkweed, Asclepias syriaca, Milkweed family, (Asclepiadaceae), https://www.illinoiswildflowers.info/weeds/plants/cm_milkweed.html
Berkov, A., 28.October.2010, Plant Talk: Inside the New York Botanical Garden; Plant Profile: The Extraordinary Common Milkweed, How Do Insects Feed on this Plant with Sticky White Latex? https://www.nybg.org/blogs/plant-talk/2010/10/science/plant-profile-the-extraordinary-common-milkweed/#:~:text=Plants%20in%20the%20genus%20Asclepias,Asklepios%2C%20the%20ancient%20Greek%20physician.
Bowe, Scott, 11.September.2018, Milkweed is More Than Just a Common Weed, WXPR, https://www.wxpr.org/natural-resources/2018-09-11/milkweed-is-more-than-just-a-common-weed
Nelson, M. and Alfuth, D., 24.February.2021, Milkweed (Ornamental Plants Toxic to Animals), X-number: XHT1276, https://hort.extension.wisc.edu/articles/milkweed-ornamental-plants-toxic-to-animals/
Taylor, David, n.d., Common Milkweed, (Asclepias syriaca L.), Plant of the Week, https://www.fs.usda.gov/wildflowers/plant-of-the-week/asclepias_syriaca.shtml
Eldredge, E.P., 2015,11,00, Milkweed Pollination Biology, Plant Materials Technical Note NV-58, Natural Resources Conservation Service, https://www.nrcs.usda.gov/plantmaterials/nvpmctn12764.pdf
Betz, R.F., Struven, R.D., Wall, J.E. & Heitler, F.B., 1994, Insect Pollinators 12 Milkweed (Asclepias) Species, T.B. Bragg and J. Stubbendieck (eds.) Proc. Of the Thirteenth North American Prairie Conference. Univ. of Nebraska, Lincoln, NE.
No author, n.d., Monarch Waystation Program, https://monarchwatch.org/waystations/
Geere, Duncan, 2010. August.19, Tiger Moths Scare Bats with Ultrasonic Clicks, Wired, https://www.wired.com/2010/08/moth-jamming/
Holm, Heather, 2017, Bees: An Identification and Native Plant Forage Guide, Pollination Press LLC
No author, n.d., Ichneumon Wasps, Discover Nature>Field Guide: Missouri Department of Conservation, https://mdc.mo.gov/discover-nature/field-guide/ichneumon-wasps
No author, n.d., Sand Wasps, Discover Nature>Field Guide: Missouri Department of Conservation, https://mdc.mo.gov/discover-nature/field-guide/sand-wasps
Berish, Chelsea, n.d., Spined Soldier Bug in Kentucky, ENTFACT-325: SPINED SOLDIER BUG IN KENTUCKY, University of Kentucky Department of Entomology, Martin Gatton College of Agriculture, Food and Environment

Common Milkweed or Asclepias syriaca is a superb Monarch support and a mainstay of Monarch waystations. But it is so much more. This plant feeds more than 450 insects at different life stages. Diverse insects consume nectar, sap, leaves, flowers and seeds⁵. Admittedly weedy, its lovely blooms are fragrant and enhance any scent garden^1,5.

Common Milkweed thrives in full sun and well-drained soils. Like other “weeds”, it’s not picky about growing conditions. A. syriaca grows in clayey, sandy or rocky calcareous soils, loamy soils and high clay or sand soils.

Asclepias syriaca springs up in disrupted areas. Human activity disrupts natural areas. But natural disruptions occur where water rises and falls, for example, along streams and lakes.

In nature, Common Milkweed is found in moist and dry black soil prairies, sand prairies, sand dunes along lake shores, fields, pastures, abandoned fields, vacant lots and along railroads, fence rows and roadsides.

Common Milkweed absolutely lives up to its weedy name. It spreads by seed and by long creeping rhizomes that pop up in unexpected places. Once established, this plant is extremely difficult to remove.

These habits are offset by Common Milkweed’s value to insects and pollinators. It’s best to let it grow where you don’t mind its vigorous and abundant nature—a wild area, a meadow or a prairie garden.

Asclepias syriaca offers a strong erect form in the garden. The pale, cylindrical central stem supports opposite jade-green leaves. These leaves range from pale to dark green on top and are pale green with short, dense hair underneath. Each leaf has a distinctive central vein with small veins spreading to the edges.

The milky sap, which gives Milkweed its name, oozes whenever part of the plant is broken. The sap is called a latex and contains 2% latex. The latex is thick and sticky.

Most ingeniously, caterpillars will reduce the sap’s flow by taking tiny bites closer to the stem. The sap leaks out there. When the caterpillar begins to eat a leaf, there’s less latex at the feeding site. Thus, less chance the sticky stuff will foul the larva’s mouth^2,3.

For humans and other mammals, there are other concerns. The milky sap contains cardenolides, specifically cardiac glycosides. Contact with the skin or eyes causes irritation. If eaten or exposed to mucous membranes, cardiac glycosides can disrupt the nervous system, the kidneys, the muscles (which includes the heart) and the human’s/animal’s acid/base balance^3,4,5.

The monarch and other insects that consume milkweed have turned this to their advantage. As the caterpillars/insects consume milkweed their bodies store the cardiac glycosides. If a bird or animal eats them, they taste bitter and can make the predator feel sick.

Predators soon learn to leave them alone. The orange/black or red/black coloring of milkweed insects signals, “Stay away! Not good for you!” The technical term for this warning coloration is ‘aposematic’⁵.

Milkweed blooms don’t dazzle but flower in 1930’s vintage shades. The drooping balls of florets are soft and dusky lasting one to one and a half months. Colors range from greenish white to greenish pink to rosy-pink to purplish-pink to reddish purple.

Each cluster averages 30 individual florets but can have up to 100. Their sweet, vanilla fragrance drifts from the three to five umbels on each plant.

Up close, each floret is a fascinating feat of engineering all directed toward an exceptional pollination system. Each a quarter of an inch across, the florets have five reflexed (bent back) petals and five raised hoods with curved horns. The hoods have lighter colors than the petals.

In the center of each floret, is a cylindrical structure formed by two fused stigmas. It’s called the stigmatic column.

Between the hoods, are the stigmatic slits. These slits hold the pollinaria. Unique structures, pollinaria hold waxy sacs of pollen. These are transferred instead of the loose, powdery pollen used by most flowers. Milkweeds and orchids are the only known plants to have them^6,7.

The milkweed pollinium (or pollinarium) consist of a blackish-brown oval gland (corpusculum) with a slit, two translator arms hanging from the gland and two pollinial sacs. Before each sac, a knee bend of approximately 90⁰ occurs in the arm. This bend enables the rotation of each sac during pollination.

In the milkweeds, the pollinial sac sit inside the stigmatic column and only the corpusculum is visible between the hood structures. When an insect lands on the flower, one of its legs may slip into the stigmatic slit between two hoods. As it tries to free itself, the leg moves upward toward the slit in the corpusculum. Bristles in the chamber keep it from going back down.

Insects must be strong to free themselves. Large butterflies, predatory wasps and long tongue bees are most likely to remove pollinaria. Lost legs and dead smaller insects both occur from failed escape attempts.

When a pollinaria is removed, it begins to dry. The pollinial sacs rotate 90^o during drying. The rotation moves them into the correct position for pollination.

When the insect lands on another milkweed, the knee bend (not the corpusculum oval) slides into the space between the hood petals. The translator arm follows then the rotated pollinial sac. The pollinial sac slides into a space in the stigmatic column and pollination is completed.

When the insect continues pulling upward, the translator arm breaks. The insect keeps the remaining part of the pollinaria.

It’s also possible to start a chain of pollinaria during this process. As the broken translator arm slides between the hoods, it can hook the corpusculum slit of this floret’s pollinaria adding a fresh pollinaria to the partial remaining one. Clumps and chains of all sorts develop this way. These groups of pollinaria may increase chances of pollination^6.7.

Part I, ends here, with the exciting conclusion of a fertilized milkweed. Part II will continue with photos and information about the insects that use Common Milkweed. What a crowd it is—including flies, wasps, bees, butterflies, moths, skippers, plant bugs and beneficial insects!

See you next time to discover what Wild Things are in the Garden!

Mary

References

Hilty, J., n.d., Common Milkweed, Asclepias syriaca, Milkweed family, (Asclepiadaceae), https://www.illinoiswildflowers.info/weeds/plants/cm_milkweed.html
Berkov, A., 28.October.2010, Plant Talk: Inside the New York Botanical Garden; Plant Profile: The Extraordinary Common Milkweed, How Do Insects Feed on this Plant with Sticky White Latex? https://www.nybg.org/blogs/plant-talk/2010/10/science/plant-profile-the-extraordinary-common-milkweed/#:~:text=Plants%20in%20the%20genus%20Asclepias,Asklepios%2C%20the%20ancient%20Greek%20physician.
Bowe, Scott, 11.September.2018, Milkweed is More Than Just a Common Weed, WXPR, https://www.wxpr.org/natural-resources/2018-09-11/milkweed-is-more-than-just-a-common-weed
Nelson, M. and Alfuth, D., 24.February.2021, Milkweed (Ornamental Plants Toxic to Animals), X-number: XHT1276, https://hort.extension.wisc.edu/articles/milkweed-ornamental-plants-toxic-to-animals/
Taylor, David, n.d., Common Milkweed, (Asclepias syriaca L.), Plant of the Week, https://www.fs.usda.gov/wildflowers/plant-of-the-week/asclepias_syriaca.shtml
Eldredge, E.P., 2015,11,00, Milkweed Pollination Biology, Plant Materials Technical Note NV-58, Natural Resources Conservation Service, https://www.nrcs.usda.gov/plantmaterials/nvpmctn12764.pdf
Betz, R.F., Struven, R.D., Wall, J.E. & Heitler, F.B., 1994, Insect Pollinators 12 Milkweed (Asclepias) Species, T.B. Bragg and J. Stubbendieck (eds.) Proc. Of the Thirteenth North American Prairie Conference. Univ. of Nebraska, Lincoln, NE.