Royal Conundrum - Killing the Monarch Butterfly with "Kindness"

The monarch butterfly population has been in serious decline for years now, something many gardeners know. To compensate for habitat loss, gardeners have been encouraged to plant more milkweeds, the insect's larval host plant. But this has led to unforeseen negative consequences, especially in warm winter regions of the U.S.

Native milkweeds can be hard-to-impossible to find, so the tropical, showy "scarlet" milkweed has become ubiquitous in garden centers across the country. This plant, Asclepias curassavica, is native to the American tropics and has spread to pantropical regions worldwide. It has become invasive in some areas, and threatens to become a pest in South Florida. 

Many monarch butterflies harbor a protozoan, Ophryocystis elektroscirrha (OE), that can weaken the adult, prevent the pupa from emerging from the chrysalis, or deform the wings. Monarchs visiting milkweeds deposit spores when they visit milkweeds. Normally, migration culls weakened individuals, and the OE spores die when the plants die back in winter. The plants grow back in spring and summer with fresh, uninfected leaves. But in areas with warm winters tropical milkweed grows all year, thus maintaining high levels of OE spores. Areas of Georgia, coastal Carolinas, Florida and the Gulf Coast have become hotspots of infection.

Monarch on Scarlet Milkweed

Apart from the immediate threat to individual monarchs, year-round milkweed is also, probably more ominously, threatening the migration itself. The presence of the milkweed affects the butterfly's hormonal balance, and works as a trigger to make it reproduce. So monarchs that find themselves in areas with warm winters don't migrate, and a year-round population gets established. With increasing warming trends this area of permanent, sickly individuals will only increase. 

Migration plays a critical role in maintaining a robust gene pool, for it culls badly infected individuals, which simply don't survive the trip. But migration may play other vital roles as well, in ways  we haven't discovered. 

Some organizations like the Xerces Society and the Florida Native Plant Society actively campaign against the use of tropical milkweeds. Some people, though, citing the drastic declines in the monarch population, feel that keeping the numbers up is of primary importance. 

Weaning gardeners away from tropical milkweed is going to be a monumental project, especially since it was promoted so aggressively as a solution to monarch population decline. 

Monarch on Asclepias curassavica

In and of itself, I'm not particularly heartbroken over the loss of scarlet milkweed in our yard. Due to neglect, they've sort of died out this spring anyway. It is a water hog, and the stems quickly get leggy and woody. It also is a magnet for aphids and spider mites, which would make any self-respecting female monarch look for greener pastures. 

Aphid-Infested Milkweed

Finding natives or even native seeds, is going to be a long, drawn out process. Some mail order nurseries offer native milkweed species that theoretically would grow here, but I'd have a better chance with offspring originating  much closer to home. 

Even though they might be the same species, a plant grown in the mid-Atlantic or Midwest would be quite different genetically from one that has adapted to South Florida conditions. They might not even look the same, they might not  survive, and they certainly wouldn't do anything to maintain genetic diversity. Ecologically even North Florida differs greatly from the southern part of the state.

Asclepias incarnata, "Swamp Milkweed," a Native

But there's a further complication!

Whether it comes to weather patterns, the density of bear fur, and many other things, matters often are much more complicated when it comes to the southern peninsula of Florida. It seems that there is an established, non-migratory monarch population south of Lake Okeechobee.  The most-studied migration routes don't cover us, especially on the sw coast, though we might get a few strays. I have had basically year-round monarchs since I began butterfly gardening around 1995. Over the years I have seen newly-emerged monarchs with deformed wings, but not a lot. Even without the scarlet milkweed, all of our native milkweeds might not go completely dormant during our winters, so a small population could persist theoretically without our help. The assumption has to be that the infection rate in our monarch population is close to 100%. 

So, in a way, it doesn't matter whether we keep planting Asclepias curassavica, but it goes against the grain now that I'm aware of a problem. While I don't like the plant, and getting rid of it would not stop the problem of diseased butterflies, it still seems somehow that replacing it with its cousins that "belong here" would be ethically as well as esthetically better. Now comes the hard part - actually doing it. 

Corkystem Passionvine

 Corkystem passionflower (Passiflora suberosa L.) is a mainstay of my butterfly garden. I just wish it would grow where I want it instead of collaborating with the birds to migrate to places where it is a pest. So far it has resisted my attempts to train it up a trellis or fence, yet it scrambles exuberantly in, around, through, and over shrubs and trees. If it has nowhere to climb, it spreads happily over the ground, especially where I have planted native heliotropium (Heliotropium polyphyllum). I could leave it as a ground cover, but since it is a vine, it presents a tripping hazard. I have a lot of digging out and potting up ahead, because I need to save at least some of the volunteers.

The genus Passiflora is the larval host for the zebra longwing, julia longwing, and much under-appreciated Gulf fritillary. The striking, orange Julias are uncommon in our garden. They tend to show up in a bunch and then disappear for years. We sometimes get zebra longwings, but they really prefer a shadier habitat than our yard offers. Zebra longwings roost in long chains at night, and the sight of such chains is absolutely breathtaking. The zebra longwing is Florida's state butterfly.

Gulf Fritillary Caterpillars on Passiflora suberosa

Zebra Longwing Caterpillar
Unripe Passiflora berries
Collier-Seminole State Park 

The beauty of a Gulf fritillary is hard to capture in paint or with my  very basic camera equipment. A newly-emerged adult gleams bright copper-orange, like the proberbial new penny. The undersides of the wings have a pattern of iridiscent silvery patches which reflect light spectacularly and brilliantly. 

The scanner cannot capture the silvery flash of the underwings.
These are dead individuals I have collected from the yard.

Passiflora suberosa is one of 7 species of passionflower native to Florida, but the purple passionflower, P. incarnata, is the only other one which occurs naturally in this area. Several exotic species, like the flamboyant scarlet passionflower ( P. coccinea) also flourish in the state. P. incarnata is a large vine, has a showy purple flower, and will get devoured by caterpillars. It dies back during our dry season.

"Maypop"  is another common name for P. incarnata. When I was a child we lived in South Carolina with my grandparents and unmarried aunt while my father served in the Korean War. I tagged along with my Aunt Iola, whom I called "Ant Ola." (I still pronounce "aunt" as "ant").

Even though I was afraid of the cows, who seemed awfully big, I liked accompanying my aunt when she took them out to pasture every morning. What I later realized was P. incarnata grew wildly in one spot. I asked her what they were, and she replied, "Maypops." When I asked her why, her answer was, "because they may pop and they may not." It is fascinating how certain little things can be preserved so vividly in our memories.

Zebra Longwing
Heliconius charitonius
Delnor-Wiggins Pass State Park

Corkystemmed passionflower is much more diminutive, and far less showy than its purple and red cousins. I agree with Rufino Osorio, who writes that while it first seems to have no obvious horticultural appeal, it's merits show themselves over time. The vine begins tender and green, and gradually adds ridges of corky material until it is enclosed completely.  Near the roots of an undisturbed vine the stem can reach a diameter of an inch or more, and certainly presents an interesting texture. 

Passiflora suberosa
Notice Corky Stem

The leaves have longish petioles and alternate around the stem. The surfaces are smooth, and the color varies from a yellowish green in bright sun to a more intense green in shade. The petioles have 2 raised "dots" opposite each other close to the base of the leaf. These are extrafloral nectaries. The plant  often displays "heterophylly," a fancy term for having leaves of different shapes. They can be simple and entire, or partially or deeply lobed. The presence of heterophylly in the plants in our yard varies, probably depending on what has been pollinated. Roger Hammer writes that lepidopterists surmise that the varying shape is a means to fool the butterflies so they don't lay as many eggs on the plant. The vine climbs and clings by tendrils emerging at the base of the leaves.

Heterophylly in Passiflora suberosa

The flower is small and delicate, about one-half to three-quarters inch in diameter. What look like petals, but really are sepals, are white or pale spring green. Pollinators of various sorts like them, because they produce a lot of berries throughout the year. The fruits start out green, turn blue, and then blue-black when ripe. Sometimes they have a chalky "bloom" like blueberries. They are roughly spherical and about a quarter-inch in diameter - about the size of a Spanish caper. They don't taste bad, but contain so many tiny seeds that they are mostly grit. Better leave them for the birds.

That brings us back to my struggle to keep the vine from eating the garden. The place it thrives most vigorously is all through and over a clump of bougainvilleas. The bougainvillea's vicious thorns and dense growth prevent me from getting at the passionvines' roots, and even if I did, the mockingbirds would reseed them promptly. They effectively cultivate the vine because they poop as they forage for the berries. The bougainvilleas aren't native, but they don't consume any resources beyond space and rainwater. The tiny white flowers nestled in the plant's hot-magenta-pink bracts attract a fair number of small pollinators, and the mess of bougainvillea branches and passiflora vines provides a prime nesting site for the mockingbirds. They have reared several successful broods there over the last few years. 

So it's a standoff. I can't beat it, so I settle for beating it back when it threatens, kudzu-like,  to suffocate the other plants. And I do like the butterflies.

Gulf Fritillary 
Agraulis vanillae
Nectaring on Blue Porterweed, Our Garden

 

Passiflora suberosa ranges from the Caribbean through Florida and the lower Rio Grande Valley, Mexico, and Central and South America. It has spread through much of the world, probably with the help of birds, and is considered an invasive exotic in serveral locales. It has a long history of use in folk medicine. It can withstand quite dry conditions if it has a little shade, but appreciates more water. It probably would not thrive in permanently soggy ground.

Sources:

Roger Hammer. Florida Keys Wildflowers. 2004. p. 127.

Rufino Osorio. A Gardener's Guide to Florida's Native Plants. 2001. pp. 290-91.

Richard Wunderlin. Guide to the Vascular Plants of Florida. 1998. pp. 443-444.