First Frost Often Means the End for Late Season Caterpillars, and a Next Chapter for the Intriguing Frostweed Wildflower

We’re finally getting our first frost in San Antonio, about three weeks after the typical November 21 first frost date prescribed by gardening buffs, farmer’s almanacs and the National Climate Data Center.

Photo by Myra  B Allison, via Ladybird Johnson Wildflower Center

Frostweed spills its guts on first frost creating a beautiful ice sculpture.   Photo by Myra B Allison, via Ladybird Johnson Wildflower Center

Freezing temps usually mean the end of the season for butterflies.   Just this week we’ve had several emails and posts from butterfly wranglers wondering what to do about caterpillars discovered outside–better to let them brave the elements, or bring them inside?

Brought 22 monarch caterpillars in from the cold. Some are already starting to make chrysalises. Some are still eating, and a few have “J’d” but after a day haven’t progressed. Anyone have any hints or advice? Hoping for the best and preparing.

–Tom Kinsey, San Antonio, via Facebook

I can argue the answer to that question either way, and have taken both routes.   A late stage Queen caterpillar was discovered on a milkweed plant in our courtyard this week.  She remained outside.

Considerations included my busy holiday schedule, a lack of host plant, and the probability that when she formed and later emerged from the chrysalis, the butterfly would face cold temperatures (making it difficult if not impossible to fly), little nectar, and few prospects for a mate.  What kind of life is that?


Frostweed is a magnet for Monarch and other butterflies in the fall, a reliable late season nectar source.  Photo by Monika Maeckle

And yet, our friend Marileen Manos Jones of upstate New York took a different tact in late October.  She convinced Southwest Airlines to fly her and a lone lady Monarch to San Antonio in early November to release the late blooming lep at the San Antonio Botanical Gardens.   No “right” answer exists to the late season caterpillar quandary.  It’s a judgment call.

The first frost of the season poses a separate natural majesty not unrelated to butterflies:  the transformation of the excellent nectar plant, Frostweed, into a beautiful ice sculpture.  I love this plant.   Such an overlooked gem.  Can’t figure out why  this easy-to-grow perennial is not sold in commercial nurseries.

In the fall, Frostweed serves as a prime nectar source for Monarchs and other butterflies.  The sturdy Verbesina virginica, with its odd square-like stalks, sports fleshy green flanges on its stems.   The wildflower produces lush white blossoms from late August through November in semi-shade that provides respite from the late summer sun.   The flowers bloom in big colonies along the rivers and streams of the Texas Hill Country.

Frostweed ice sculpture

Frostweed ice ribbons are always a nice surprise. Photo via Ladybird Johnson Wildflower Center

Along our stretch of the Llano River, Frostweed lines the riverbanks.  This last year took a toll on the flowers, as the water table had receded significantly from the 2011 drought.  Many Frostweeds died as stiff stalks in August.

But in general, this plant is gorgeous, drought toleranat, a generous seed and nectar producer, and the butterflies love it.

As a member of the aster family, Frostweed  can reach six-eight feet in height in a good year. Upon first frost, the stem splits, the sap oozes out and freezes to form fascinating curled ice ribbons and intriguing sculptures. That’s why it’s called Frostweed, or sometimes, Iceweed.

Frostweed Seed

Frostweed produces generous seed and nectar. And it’s easy to grow.   Photo by Monika Maeckle

Only a handful of species commonly exhibit this behaviour, according to Dr. James Carter’s website.   Dr. Carter coined the term, crystallofollia, to describe the phenomenon, from the Latin crystallus, ice, and folium, leaf.   Dr. Carter also points out that “the ice formation far exceeds the amount of moisture from sap locally available in the stem, and must be augmented by water drawn up from the roots.”   Frostweed’s rhizomes help it slurp up moisture in the soil to produce the ice formations.  The robust root system also makes it easy to propagate the plant from its roots as well as from seed.

For a fascinating blow-by-blow of what actually occurs botanically in the forming of these sculptures, see Bob Harms’ Biophysica of Crystallofolia website.   It humbles the most talented artist.

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11 thoughts on “First Frost Often Means the End for Late Season Caterpillars, and a Next Chapter for the Intriguing Frostweed Wildflower

  1. Sunday Nov 3rd I saw 3 Monarchs and a variety of others in flower beds at the Texas Transportation Museum Garden Railroad on Wetmore Road.

  2. I have 17 chrysalis in my home right now. I have already let 4 Monarchs free during the warm days this past week. I have 17 more waiting to arrive. I am concerned about one that has finally turned black/clear. It’s been 3 days and I still can’t see the wings inside, in fact it’s a little cloudy. Is this chrysalis in trouble?

    • Might have OE. Best to destroy it. Flush it. I know, it’s hard, but the right thing. You don’t want to release an infected butterfly out into the wild, as it will just spread disease.

      • A much better way to euthanize , is to put them in the freezer. They just go to sleep..forever 😥 I know it’s hard,but sometimes necessary . Hope this helps!

        • thanks for the response. I knew when a chrysalis turns black it should be discarded. The chyrsalis did turn black on the 16th day, yesterday, and I removed it from the cage. The other is still green. I will wait until it turns black and remove it. I have 8 other newly formed chrysalides and I decided to bring the cage indoors as we are expecting temps of 31degrees a couple of nights this week. I knew about the methods of euthanasia and I don’t have any problem with doing this when its appropriate. My question still remains “do lower temperatures create longer intervals of metamorphosis within the chysalis”? If we even know this. Is there a chance butterflies can survive and still migrate when night time temps are in the mid to high 30’s and 40’s and the daytime temps are in the 60’s? Thanks!

  3. I like to looks of this plant. Could I grow it in my garden in Zone 6b NEOk??
    I don’t have a formal garden and I have common milkweed, butterfly weed and Tropical milkweed in my garden already.
    If so where can I get seeds.?
    Thank you for your time.

  4. I just started raising monarch from eggs i have collected. They hatch and grow well, form their button and go into a J but the first 4 have only formed like a “helmet” of their chrystallis and then they eventually die. Ine took over 12 hours trying to form his chrystallis after forming his helmet.
    Can you give me any suggestions. I am in Beverly Hills Florida which is central and near the gulf coast.

  5. I have 11 late Queen caterpillars. They will probably not emerge until close to Thanksgiving. I brought them in. I wanted them to at least have a fighting chance. If they have no chance of making it in the real world, what do you think of an existence inside with children being able to watch the process? That sounds like a better life than freezing or starving to death to me. What do you think? Do the Queens migrate to Mexico as well?

    • It’s not my call, but “butterfly houses” exist all over the country to highlight the beauty and majesty of butterflies. You will need lots of nectar plants, but can also supplement with sponges soaked in gatorade. Let us know what you do and how it goes! –MM

  6. I live in San Jose, California and have been bringing monarch caterpillars into my cage on milkweed plants since September. Right now I have 2 chrysalides that look a healthy green but have not opened in 16 days.
    this has not happened to me before and I am concerned.
    The outside temperature the past 3 nights has been about 37 degrees and the daytime temp is 61. Would the temperature have anything to do with this length of time for metamorphosis?

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