Fresh News About Monarch Butterflies

Standard

Monarch butterfly (Danaus plexippus). Photo: Kenneth Dwain Harrelson, Wikimedia Commons

I’ve written about the monarch butterfly (Danaus plexippus), the world’s best known migrating lepidoptera, whose annual 3,000 mile/4,800 km migration from the mountains of Mexico to edge of the boreal forest in Canada is the stuff of legend, more than once in this blog (Monarch Butterflies Are Back!Plant More than Milkweed to Save Monarchs and Monarchs Arrive in Europe!, for example), but there is much research going on about them and scientists learn more about monarchs each year. 

Here are some interesting recent discoveries:

Winter Numbers Down

Some monarchs are tagged so their migration can be followed. Photo: Katja Schulz, flickr.com

Sadly, Mexican authorities report that the number of monarch butterflies overwintering in Mexican forests was down by half during the 2019–2020 winter season. Just 7 acres (2.83 hectares) was covered, a 53% decrease from the 2018–2019 season, when monarchs covered 15 acres (6.05 hectares) of forest.

Jorge Rickards, the managing director of WWF-Mexico, noted that this is not necessarily a cause for alarm, but added that “we must remain vigilant and not allow it to become a trend in the coming years. Conservation is a long-term job.”

New Colony of Monarch Butterflies Discovered in Mexico

Butterflies at the newly discovered Nevado de Toluca colony. Photo: keteka.com

For a long time, it was thought that there was only one colony of monarchs in Mexico, at what is now the Monarch Butterfly Biosphere Reserve in the state of Michoacán, but a second one was recently discovered near the Nevado de Toluca volcano, a good 4-hour drive to the southeast. 

For years, locals had remarked the presence of limited numbers of monarchs in the vast (53,419 ha) Nevado de Toluca National Park during the winter, but no one was able to find whether they were just stragglers or if there was a colony hidden there. Just before Christmas in 2018, however, a routine park patrol finally did find a large colony clinging to oyamel firs (Abies religiosa) at an altitude of more than 3,000 meters. In 2020, researchers returned to study the situation and calculated that there were about 20 million monarchs in the new colony, enough so tree branches bend under their weight.

Curiously, while the colony at the Monarch Butterfly Biosphere Reserve stays on the same trees all winter, which has made it into a tourist attraction, the new colony at Nevado de Toluca moves every night, so is harder to find and study.

Local governments currently have no plans to open this new colony to mass tourism.

Plant the Right Milkweed

We all know that monarch caterpillars will only feed on milkweeds (Asclepias spp.) and a few other closely related species, but it turns out that the milkweed species you plant to feed visiting monarchs is very important. 

The most commonly grown garden milkweed, butterfly weed (Asclepias tuberosa), turns out to be a bit of a dud when it comes to feeding monarch caterpillars. Photo: H. Zell, Wikimedia Commons

Butterfly weed (Asclepias tuberosa), the most common milkweed offered in garden centers and a popular garden perennial, is actually the least favorite milkweed species and monarch caterpillars rarely feed on it. It doesn’t have the milky sap of other milkweeds and there may be something in that sap that female monarchs seek when looking for a place to lay their eggs. 

Monarchs seem to like common milkweed best (A. syriaca). Photo: Stefan.lefnaer, Wikimedia Commons

The species most frequented by monarchs is the common milkweed (A. syriaca), a weedy species rarely grown in gardens. One study showed that 85% to 92% of monarchs overwintering in Mexico had fed on common milkweed as caterpillars. That said, most other species studied so far are good host plants as well, including another fairly popular garden species, swamp milkweed (A. incarnata). Apparently, it’s only butterfly weed (Asclepias tuberosa) that isn’t really worth planting if your goal is to provide a host plant for monarch caterpillars..

Monarch caterpillars like hybrid plants as well as species. Photo: Maria L. Evans, Wikimedia Commons

Another study challenges the commonly repeated belief that only wild species of milkweed should be used in butterfly gardens. It found that hybrid milkweeds are just as attractive to egg-laying females as straight species. 

Cut Your Milkweeds Back 

Cutting back milkweeds before they bloom makes them more attractive hosts for caterpillar larvae. Photo: http://www.greentecnursery.com

Research by Nate Haan of Michigan State University shows that female monarchs prefer to lay their eggs on fresh young stems that haven’t flowered yet rather than tougher, aging ones. That’s not a problem early in the season, but Haan discovered that cutting back a third of a garden’s milkweeds in June and another third in July resulted in more monarch butterfly eggs being laid on the resprouting plants. This heavy pruning doesn’t harm the milkweed plants and they quickly rebound.

The tropical milkweed (A. curassavica) may actually disrupt monarch mutation if it isn’t cut back. Photo: Renjusplace, Wikimedia Commons

And cutting back would be a good solution to another dilemma. The tropical milkweed (A. curassavica) is the most popular garden milkweed in the southern U.S., but its habit of continuous bloom well into fall and even winter can be harmful to migration. It’s believed monarchs tend to stop on patches of this plant rather than continue their trip south in a timely manner, disrupting migration. Also, a debilitating protozoan parasite (Ophryocystis elektroscirrha) tends to build up in tropical milkweed, at least in areas where it isn’t killed back by frost in winter, and can weaken caterpillars and cripple adult butterflies. 

Both these flaws can be easily mitigated by cutting tropical milkweed back hard in the fall. With the plant absent from the landscape, the butterflies will continue their migration normally and won’t be as likely to become infected with the disease.

Let Them Be Free

Mass butterfly releases aren’t helping save monarchs! Photo: http://www.brainerddispatch.com

Apparently, monarchs raised indoors as caterpillars largely fail to migrate. They just don’t seem to pick up on the clues (colder weather, dieback of blooming plants) that tell wild-born monarchs it’s time to head south, according to biologists Ayse Tenger-Trolander and Marcus R. Kronforst of the University of Chicago. 

That means the thousands of monarchs sold by butterfly farms to schools, weddings, funerals and other events for mass butterfly releases may be good publicity for the monarch cause, but don’t directly help monarch survival in any way, as they simply are not flying back to Mexico. 

Planting Flowers to Feed Adults

The common belief that planting milkweeds (Asclepias spp.) is all you need to do to save monarchs is incorrect. True enough, female monarchs will only lay their eggs on milkweeds and their caterpillars will only feed on those same plants, but adult monarchs feed on nectar of a wide range flowers. In fact, don’t even particularly like milkweed flowers (they are instead largely pollinated by bees and wasps). 

Why not create a monarch way station? But drop letter B (Asclepias tuberosa) from the list of good monarch butterfly plants. (Read above to see why.) Photo: http://www.wegarden.ca

If you want to create a garden for monarchs (and why not officially start a monarch waystation?), you need to grow more than milkweeds. Instead, try to provide a wide range of flowers, making sure that there are some in bloom throughout the entire growing season (read Plant More than Milkweed to Save Monarchs), especially at the extreme ends of the gardening season, that is, early spring and late fall.

Also, it’s turning out that mixed plantings actually confuse butterflies. They use sight to find their food, relying on plant shapes. So, a “butterfly meadow,” with flowering plants mingling any which way, might not be the best solution. Instead, you’ll get more positive results by growing single plants isolated from others by mulch. And planting in a north-south pattern is best. 


So, now you know what to do to make your garden more monarch butterfly friendly!

Recognizing Butterfly Flowers at a Glance

Standard

20160402A

Like most butterflies, the black swallowtail (Papilio polyxenes) prefers clustered flowers.

Like all good pollinators, butterflies have preferences about the flowers they visit. In particular, most are less adept than bees and hummingbirds at flitting from flower to flower, a movement which requires quite a bit of energy. They therefore prefer flowers where they can perch for a while, flowers that contain nectar that they can slurp up slowly rather than in a mad rush. That’s why they prefer clustered flowers.

20160402B

The daisy is a composite flower: hundreds of fertile, nectar-rich florets in the center with a halo of sterile flowers act as a landing platform all around.

Asteraceae flowers (daisies, coneflowers, zinnias, etc.) are the perfect example of what a “butterfly flower” looks like. Each “bloom” may look like a single flower, but is are in fact a composite flower, that is an inflorescence composed of a dense disc of fertile florets in the center (disc flowers) and surrounded by sterile flowers called ray flowers. Ray flowers evolved specifically to attract the attention of insects like butterflies: first their color draws butterflies from afar, then they are placed in a ring all around the fertile florets, allowing them to act as a landing platform. When a butterfly alights on the platform, it’s offered a large number of fertile florets filled with nectar. So it stays there a while, dipping its proboscis into floret after floret. And as it drinks, the butterfly is covered with pollen that will fertilize the next inflorescence it lands on.

20160402C

The wild carrot forms an umbel of fertile florets that attract butterflies.

Obviously, it’s not just Asteraceae flowers that have grouped flowers and pretty much any plant with that feature will a attract butterflies. Flowers in umbels (dome-shaped clusters), notably, like those of wild carrots, milkweeds, and clovers, will also attract butterflies.

Finally, butterflies are also attracted to large flowers that are filled with nectar, like daylilies and lilies. Their enormous petals also make great landing platforms.

Perfume Helps Too

Most butterflies are also attracted to fragrant flowers. In general, butterflies prefer flowers with an intense, sweet fragrance over ones with a musky scent.

A List of “Butterfly Flowers”

There are literally thousands of flowers that you can plant to attract butterflies: here is a very partial list.

  1. Ageratum (Ageratum houstonianum) annual
  2. Allium (Allium spp.) zone 3
  3. Arabis (Arabis spp.) zone 4
  4. Aster (Aster spp.) zone 4
  5. Astilbe (Astilbe spp.) zone 4
  6. Aubrieta (Aubrieta deltoidea) zone 4
  7. Azalea (Rhododendron spp.) zones 2 à 10
  8. Batchelor’s buttons (Centaurea cyanus) annual
  9. Beebalm (Monarda spp.) zone 3
  10. Black-eyed Susan (Rudbeckia spp.) annual or zone 3
  11. Blanket flower (Gaillardia spp.) annual or zone 3
  12. Blazing star (Liatris spp.) zone 3
  13. Blueberry (Vaccinium spp.) zones 3 à 5
  14. Buddleia (Buddleia davidii) zone 6b
  15. Butterfly bush (Buddleia davidii) zone 6b
  16. Candytuft (Iberis spp.) annual or zone 3
  17. Carnation (Dianthus spp.) annual or zone 4
  18. Catmint (Nepeta spp.) annual or zone 4
  19. Chrysanthemum (Chrysanthemum spp.) annual or zones 4 à 7
  20. Cleome (Cleome hasslerana) annual
  21. Clover (Trifolium spp.) zones 2 à 9
  22. Common lilace (Syringa vulgaris) zone 2b
  23. Coneflower (Rudbeckia spp.) annual or zone 3
  24. Coreopsis (Coreopsis spp.) annual or zone 3
  25. Cosmos (Cosmos bipinnatus) annual
  26. Dahlia (Dahlia spp.), bulbe tendre
  27. Daisy (Leucanthemum spp.) zone 3
  28. Dame’s rocket (Hesperis matronalis) zone 3
  29. Dandelion (Taraxacum officinale) zone 3
  30. Daylily (Hemerocallis spp.) zone 3
  31. Dill (Anethum gravolens) annual
  32. Echinacea (Echinacea purpurea) zone 3
  33. False indigo (Baptisia spp.) zone 4
  34. Fennel (Foeniculum vulgare) fine herbe annual
  35. Fleabane (Erigeron spp.) annual and zone 3
  36. Gaillardia (Gaillardia spp.) annual or zone 3
  37. Globe thistle (Echinops ritro) zone 3
  38. Golden marguerite (Anthemis tinctoria) zone 3
  39. Goldenrod (Solidago spp.) zone 3
  40. Helen’s flower (Helenium spp.) zone 3
  41. Heliotrope (Heliotropium arborescens) annual
  42. Hollyhock (Alcea spp.) zone 3
  43. Honeysuckle (Lonicera spp.) zone 3
  44. Impatiens (Impatiens spp.) annual
  45. Indian hemp (Apocynum spp.) zone 3
  46. Joe Pye-weed (Eupatorium spp.) zone 3
  47. Lantana (Lanata camara) annual
  48. Lavender (Lavandula spp.) zones 5 to 9
  49. Liatris (Liatris spp.) zone 3
  50. Lily (Lilium spp.) zones 3 to 10
  51. Lupine (Lupinus spp.) annual or zones 2 to 8
  52. Lychnis (Lychnis spp.) zone 3
  53. Mallow (Malva spp.) zone 3
  54. Marigold (Tagetes spp.) annual
  55. Mexican sunflower (Tithonia rotundifolia) annual
  56. Mignonette (Reseda odorata) annual
  57. Milkweed (Asclepias spp.) zones 3 à 10
  58. Nasturtium (Tropaeolum majus) annual
  59. Nepeta (Nepeta spp.) annual or zone 4
  60. Pansy (Viola x wittrockiana) annual
  61. Pearly everlasting (Anaphalis margaritacea) zone 3
  62. Petunia (Petunia x hybrida) annual
  63. Phlox (Phlox spp.) annual or zone 3b
  64. Pincushion flower (Scabiosa spp.) annual or zone 3
  65. Pink (Dianthus spp.) annual or zone 4
  66. Primula (Primula spp.) zones 2 à 9
  67. Privet (Ligustrum spp.) zones 4b à 9
  68. Pussytoes (Antennaria spp.) zone 2
  69. Rhododendron (Rhododendron spp.) zones 2 à 10
  70. Rudbeckia (Rudbeckia spp.) annual or zone 3
  71. Rue (Ruta graveolens) zone 4
  72. Ruellia (Ruellia spp.) annual or zone 6
  73. Russian sage (Perovskia spp.) zone 3
  74. Sage (Salvia spp.) annual or zones 3 to 11
  75. Scabiosa (Scabiosa spp.) annual or zone 3
  76. Sedum (Sedum spp.) zones 2 à 10
  77. Spider flower (Cleome hasslerana) annual
  78. Staghorn sumac (Rhus typhina) zone 3
  79. Sunflower (Helianthus annuus) annual
  80. Sweet alyssum (Lobularia maritima) annual
  81. Thistle (Cirsium spp.) zone 2
  82. Verbena (Verbena spp.) annual
  83. Viburnum (Viburnum spp.) zones 2 à 8
  84. Violet (Viola spp.) zones 1 to 8
  85. Viper’s bugloss (Echium spp.) annual or biennial, zone 4
  86. Yarrow (Achillea spp.) zone 3
  87. Zinnia (Zinnia spp.) annual

In closing, attracting butterflies can be even simpler than following a list of flowers. Simply plant more blooms, of any kind, and less lawn, and you’ll soon find yourself with a butterfly haven!