Where are the monarch butterflies? They're MIA on the four species of milkweed in our Vacaville pollinator garden
But milkweed attracts other insects, including honey bees, carpenter bees, bumble bees, assassin bugs, syrphid flies, leafcutter bees, Anthophora (genus) bees, wasps, praying mantids, and butterflies, including Gulf Fritillaries, Agraulis vanillae, and gray hairstreaks, Strymon melinus. And yes, arthropods such as crab spiders and orbweavers visit, too.
On Sept. 19, we witnessed a gray hairstreak laying eggs on the buds of a tropical milkweed, Asclepias curassavica, which we planted in a container with another milkweed, butterflyweed, A. tuberosa. (Yes, we give the monarchs a choice; we also offer them showy milkweed, A. speciosa, and narrowleaf milkweed, A. fascicularis, and we cut back the A. curassavica before the fall migration, as noted entomologists recommend.)
Butterfly guru Art Shapiro, UC Davis distinguished professor of evolution and ecology, says this about the gray hairstreak on his website, Art Shapiro's Butterfly Site:
"This is one of the most polyphagous butterflies known, recorded on host plants in many families. Its most frequent hosts in our area are mallows, including the weedy species of Malva; legumes, including Spanish Lotus (Lotus purshianus), Bird's-Foot Trefoil (Lotus corniculatus), White Clover (Trifolium repens) in lawns, Alfalfa (Medicago sativa) and many others;and Turkey Mullein (Eremocarpus or Croton setigerus, Euphorbiaceae)."
So, we mentioned the gray hairstreak laying eggs on the buds of the milkweed. "Is this a host plant, too?"
"Apparently on the flower buds! Never before recorded--in fact, I have no records on Asclepiadaceae/Apocynaceae at all," Shapiro said. "They lay on Callistemon (bottlebrush) too..."
Meanwhile, update: no monarchs, no eggs. We're still waiting.
But "yes" on the gray hairstreak, Strymon melinus, and "yes" on her eggs.
Don't tell the honey bees.
They will forage where they want to--whether it's on bee balm, a dandelion or that controversial tropical milkweed, Asclepias curassavica.
Just before we cut back the tropical milkweed for the season, the honey bees got their last hurrah--the last bit of nectar for the year.
Why cut back tropical milkweed? Scientific research shows that this plant disrupts the monarch migration patterns when it's planted outside its tropical range, and can lead to the spreading of OE, orophryocystiselektroscirrha, a protozoan parasite that infects monarch and queen butterflies. So we gardeners cut it back AFTER the monarchs have quit laying their eggs for the summer (or early fall) and BEFORE the monarch migratory season.
Honey bees, however, do love that milkweed. (Note that some scientists, conservation organizations and horticulturists urge folks NOT to plant the non-native tropical milkweed, and if they do, cut it back before the migratory season. See post from Xerces Society of Invertebrate Conservation.)
Connie Krochmal's article on "Milkweed as Honey Plants" in the Aug. 23, 2016 edition of Bee Culture magazine points out just how much bees love milkweed.
"Very fond of milkweed blossoms, bees will desert other flowers when these are available. The plants provide a good nectar flow. Bees discard the pollen. Assuming enough plants are available, milkweeds can bring a good crop of honey."
Milkweed, Krochmal writes, "are major bee plants in the North Central states, the Northeast, Southeast, the Plains, and the mountainous West." The honey is typically light colored and mild-flavored, she added.
"Generally, milkweeds are considered beneficial to bees. However, there are potential negative aspects to milkweed flowers. It is conceivably possible for bees and other small pollinators to become trapped in a blossom. Also, the sticky pollen masses might cling to a bee's head or legs, thereby affecting her mobility or appearance."
Yes, it does. We've seen many a bee struggle to free herself from the pollinia. Some lose their legs. Some perish.
But that nectar--that nectar--the bees keep coming back for more.
We plant three species of milkweed (the host plant for the monarchs), but both the monarchs and the honey bees gravitate toward A. curassavica, a non-native. So do syrphid flies, carpenter bees, bumble bees, leafcutter bees and assorted other insects.
If you haven't heard, planting tropical milkweed is controversial. Scientific research shows that it disrupts the monarch migration patterns when it's planted outside its tropical range, and can lead to the spreading of OE, orophryocystiselektroscirrha, a protozoan parasite that infects monarch and queen butterflies. (See Exposure to Non-Native Tropical Milkweed Promotes Reproductive Development in Migratory Monarch Butterflies, published by the National Center for Biotechnology Information, U.S. National Library of Medicine, Bethesda, Md. Also see the Xerces Society for Invertebrate Conservation website on the issue.)
UC Davis alumnus and monarch expert Anurag Agrawal of Cornell University, the James A. Perkins Professor of Environmental Studies at Cornell University and the author of the celebrated book, Monarchs and Milkweed: A Migrating Butterfly, a Poisonous Plant, and their Remarkable Story of Coevolution (2017 Princeton University), knows the controversy well.
"Tropical milkweed is an interesting and complex issue," he recently told us. "I love the plant for various reasons, but there is growing evidence that as it has become weedy (and self-seeding) in the southeastern United States and California. It is affecting monarchs, mostly by disrupting their migration. The key issue here is that when it is flowering 'out of season' this can be 'confusing' to monarchs. Having said this, we don't live in a pristine world, so my position is that we need moderation in the approach to tropical milkweed. It is certainly an easy plant to grow and monarchs can make good use of it during the caterpillar season. If you love the plant, go for it, but I would recommend cutting in back before the migratory season starts."
Three Milkweed Species
We offer monarchs a choice of milkweed species in our Vacaville pollinator garden. In addition to the non-native A. curassavica, we plant two native species: narrowleaf milkweed, A. fascicularis, and showy milkweed, A. speciosa. In July, we collected 11 caterpillars from the narrowleaf milkweed; we rear them to adulthood and release them into the neighborhood. But in the numbers game, the tropical milkweed won. From July through today, we have collected a whopping 43 eggs or caterpillars from A. curassavica. How many from A. speciosa? Sadly, none.
As recommended, we cut back or remove the tropical milkweed before the migratory season. In the meantime, we grow it for three reasons: (1) for the monarchs (2) as a food source for other insects and (3) as an ornamental garden plant. We like the brilliant colors and the diversity of insects it attracts.
On one afternoon in late July, we photographed foraging honey bees on the spectacular blossoms. They just couldn't get enough of it.
Ever seen a back-lit monarch butterfly?
It's like a stained-glass window in a centuries-old steepled church where you cannot see the ugliness of the world, but its beauty.
Monarchs are like that. Those iconic butterflies excite, inspire and transform you, just like stained glass windows.
We captured these images at dusk of a monarch fluttering around an aphid-infested milkweed, a tropical milkweed, Asclepias curassavica, on Aug. 7 in Vacaville, Calif.
The orange butterfly was nothing but a blur until we stopped the action (1/4000 of a second) with a 200mm macro lens mounted on a Nikon D500.
The beauty (the monarch) eclipsed the beast (oleander aphids) in a moment of time.
If you've ever stepped in sticky gum, it's similar to what happens when an insect steps into milkweed pollinia.
Take the wasps visiting the tropical milkweed (Asclepias curassavica) on Thursday morning, July 16 in the UC Davis Arboretum and Public Garden.
They foraged on the colorful red, yellow and orange blossoms, and as nature intended (for reproductive reasons), flew off with that sticky pollinia from the anthers.
Basically, pollinia is a sticky packet of golden pollen grains originating from a single anther. The wishbone-shaped pollinia are in a nectar trough where insects often get trapped. Some insects manage to escape but leave body parts behind. A foot here...a wing there...an antenna over there...
One wasp exited a flower with "the golden glue" on its feet.
“Too funny with all the milkweed pollinia all over its feet,” commented Lynn Kimsey, director of the Bohart Museum of Entomology and Nematology and professor of entomology at UC Davis, who identified the wasp as a species of Podalonia, parasitoidal wasps in the family Sphecidae. "It looks like it's wearing fluffy socks.”
We've seen honey bees on showy milkweed (Asclepias speciosa) struggling to free themselves, only to find the bees dead the next day--and new recruits buzzing in for their share.
These Podalonia wasps, however, managed to navigate the "traps" quite well.
They'll be back for another round.
(Reminder: Folks planting the tropical milkweed in temperate zones (like here in Davis, Calif.) must remove or cut back the tropical milkweed by winter. "A protozoan parasite of monarch butterflies, Ophryocystis elektroscirrha or OE for short, can travel with monarchs visiting the plants and become deposited on leaves," explains the Xerces Society for Invertebrate Conservation.)