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.)
The monarch caterpillar feasting on the tropical milkweed, Asclepias curassavica, in Vacaville, Calif., kept doing what monarch 'cats do best--eat.
She insisted on devouring the leaves as if there were no tomorrow--and today would end soon.
How did we know her gender? Our Danaus plexippus pupated, formed a chrysalis, and emerged. Oh, you beautiful gal!
Folks who comment that someone is "eating like a pig" or "eating like a horse" or "wolfing it down," have probably never seen a monarch caterpillar chow down, scarf it up or shovel it in.
One minute our little 'cat is stretched out on a leaf, binge eating. The next minute the leaf is gone and she's porking out on a second leaf. And scouting for a third.
Eric Carle titled his classic children's book, "The Very Hungry Caterpillar," quite well. His little 'cat ate everything in sight: gobbling, guzzling, gorging and gulping down everything from fruits and vegetables to junk food.
Remember the story? First, the little 'cat ate an apple, two pears, three plums, four strawberries, and five oranges but was still hungry. Famished, really. So he ate a piece of chocolate cake, a lollipop, a piece of cherry pie and a cupcake...and more...and he wasn't little anymore.
Many folks sheltering at home during the COVID-19 crisis can certainly identify with the snatch-and-grab menu of "The Very Hungry Caterpillar."
Did someone say "chocolate cake?"
(Editor's Note: Those planting the tropical milkweed in temperate zones (like here in Vacaville,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.)
Picture this during National Pollinator Week: five monarch caterpillars and assorted honey bees sharing tropical milkweed.
It was love at first bite. Or love at first sip.
The 'cats kept munching and the bees kept foraging. Neither species seemed interested in the other.
But the adult monarchs definitely showed more interest in the tropical milkweed (Asclepias curassavica), a non-native, than the other two species, both natives, that we planted: the narrow leaf (A. fascicularis) and showy milkweed (A. speciosa).
They laid eggs only on the tropical milkweed, and so far, have produced five caterpillars.
The score to date:
Tropical milkweed: 5 caterpillars
Narrow leaf milkweed: 0
Showy milkweed: 0
Reminder: Folks planting the tropical milkweed in temperate zones (like here in Vacaville,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.
Yes, indeed. But meanwhile, we're witnessing untold sharing on the wildly popular tropical milkweed by not only monarch caterpillars but honey bees, syrphid flies, bumble bees, carpenter bees, leafcutter bees and sweat bees.
We gardeners and photographers are also drawn to the spectacular red, orange and yellow flowers that add both beauty and color to a cherished pollinator patch in the midst of the COVID-19 pandemic...and National Pollinator Week.