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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29 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!

          • Several years ago in Louisiana, I found caterpillars and brought them into our classroom. They formed their chrysalis and then nothing happened for several months, through the winter. I figured they were dead but left them in their containers for the students to study and enjoy. To our surprise, after a hot weekend in May, we found them emerging! We watched this amazing transformation, took pictures, and released them!

  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

      • I live in Los Angeles, California where after years of drought the rains have come. I am thinking of keeping my soon to be butterflies inside. Right now I have 6 caterpillars.. I have plenty of Pentas growing outdoors. Do the butterflies need fresh on the bush flowers or will cut flowers be ok? Also, is only one type flower ok, or do they need a variety?

        • Hi i also live in Los Angeles, I don’t have any nectar plants available right now. do you know of any places near Los angeles that the monarchs are overwintering? I have 3 butterflies now and in a few days i should 4 more.

          • I live in San Jose and in mid December I drove my last butterfly of this season to Natural Bridges in Santa Cruz and released it. The eucalyptus trees in Natural Bridges had many monarchs even though winter was already happening. I think the weather in LA is more then satisfactory for Monarch survival when compared to No California. Good luck!

  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?

    • I think so based on my experience one year in LA.. See my post above, but basically they stayed in the chrysalis stage through the winter, and emerged in May when it got hot! Don’t give up on them yet!

  7. I live in New Zealand, on my plants I have tiny catapillars, we are expecting a bad storm, should I collect all the babies and keep them inside until the weather clears or can they survive by themselves?

    • Yes, they can survive in all stages, except the butterfly stage. Butterflies can’t fly in the cold, rain, or cloudy skies. Butterflies need sun to fly and guide them (natural instincts).
      But all the other stages of Monarch butterflies can survive during a storm. I live in Pensacola, Florida and we had a severe storm with a Tornado and the Monarch eggs, caterpillars, and pupas all survived just fine. They have ways of adhering themselves to leaves and stems in the garden. Its amazing!

  8. I have about 14 Monarch caterpillars in my sport tent ( 4ftx4ftx6ft- made to hold one lawn chair and zip up to shield from cold and rain) which works perfect as a butterfly habitat. Today, I was blessed to find milkweed plants at Lowes and going to buy 2 more containers tomorrow giving me 12 blooming plants. Is it possible to keep the Monarchs in this habitat all winter and release the Monarch butterfly in the spring. I live in Louisiana and it’s been so wet this winter, I feel the Monarch will have difficulty surviving in the cold wet winter to migrate. I just wonder with the blooming milkweed, can the Monarch stay in my habitat all winter?

  9. I live in South Australia its July in the middle winter and probably 2 month left of winter I have about 12 cats all different sizes on my swan plants what should I do bring them in or leave them , I’m just concerned if I bring them in and they turn into butterflys how long can they survive inside help please Suzanne

    • Hi Suzanne, I live in Gosford NSW and bought my last caterpillar into our sunroom where it turned into a chrysalis on a reed decoration. Bought it inside to be warmer at night, and it hatched yesterday. I put it out on a flowering shrub for a day, but it never moved…
      Currently feeding the butterfly with watered -down honey in an eyedropper . It sits on a potted flower all day and steps onto my finger to be fed. ( you might have to put a nurses uniform on to feed 12 of them ! good luck.)

  10. I have 4 milkweed plants, 2 swamp aka incarnata and 2 prairie aka sullivantti, which I planted in early May in central Illinois. The incarnatas are 44″ and 30″ tall and the sullivantii are 30″ and 27″. I also have a tuberosa, which is supposed to be good for nectar (19″ tall). We having good weather with lots of sun interspersed with rain.

    But so far I don’t have any Monarch eggs. How can I get them?

  11. some one gave a friend who then gave it to me a screen/net type container in which I put caterpillars until they developed into chrysalis after which the monarch is born. I cannot find one anywhere. It could be folded when not in use. I used it and hung outside but it was a good container to protect them from wasps and spiders. The net became rotted and torn and no longer served its purpose. Where can I find another one?

    • Bass Pro Shop sells them in their gift shop with the children’s things for $20. I think you can get them online at Walmart, too. Can look for them online and have delivered to your house.

  12. Two days ago I found four black swallowtail catipillars on my parsley plant. I brought the plant into my three season porch. Today, when I got home from work, I found one crawling up the screen, one under the railing, one still on the parsley plan, and unfortunately I cannot find the four one. The two “wanderers” I put in glass jars covered with cling wrap and holes for air, with a twig and a piece of parsley. They have assumed the J position and have stopped moving. I live in Connecticut and the days are still warm. Do I need to add water to the habitat? Should I keep them in full sun? I don’t have any experience in raising butterflies and wanted to protect them from birds in the garden. Any advice would be most appreciated! Thank you!

  13. Nice article! I have 6 Swallowtail chrysalis in an aquarium – in doors – it’s now late October and they have been in this stage for 5-6 weeks now. So these may finally finish and come out in mid winter? If so, is there a way to keep them until warmer weather or just let them go and hope for the best.

    Thanks for you answer

  14. I recently brought in my potted plants and discovered 4 caterpillars on one that contains some citronella. I am thinking they are black swallowtails and am hoping to get to watch them become butterflies! I’m looking for the best ways to assist them through their development stages!!! Help and guidance on the task is welcome!!!

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