On a recent walk through a local meadow I spotted a bank of Field Thistle (Cirsium discolor).
It was eye-catching for two reasons. The sight of the plant itself is arresting, with its tall candelabra-like shape topped with purple pompoms of flowers instead of candle flames. But it was the sight of so many visitors to the flowers, often several on a single flower head, that was really breath-taking. Bumble Bees, Honey Bees, Clearwing Moths and so many different butterflies moved quickly from flower to flower, pausing briefly to dine. Field Thistle presents a sumptuous feast for potential pollinators!
At one ‘banquet table’, a Honey Bee, a Thistle Long-horned Bee (Melissodes desponsus) and a Hummingbird Clearwing Moth all dined amiably together.
At another, several Bumble Bees, Honey Bees and Thistle Long-horned Bees shared a meal.
How is it that one flower head can accommodate so many visitors simultaneously? Field Thistle is a member of the Aster or Composite (Asteraceae) family. Each of the purple pompoms consists of a cluster of many long narrow tubular disk flowers. You can see the individual flowers in the head in the lower part of the photo below.
The Long-horned Thistle Bee in the photo below is actively eating both pollen and nectar, and harvesting more to provision her nest for her larvae. You can see the pollen she has collected packed onto hairs, called scopae, on her hind legs. We know this is a female, because only female bees harvest food for their offspring. This bee species specializes on pollen from Field Thistle and a few other closely related plants (all of the genus Cirsium) for her larvae. This makes her an excellent pollinator for Field Thistle, since she won’t be visiting other flowers. It also means that without these thistles, this bee species would not survive. It’s the same concept as the Monarch butterfly’s dependency on Milkweeds (Asclepias species) for survival, because Milkweeds are the only food their caterpillars can eat.
Although it appears in the photos above that the various visitors to these flowers are happy to share the wealth of the Field Thistle banquet, I’m sorry to have to report that the Honey Bees actually indulged in bullying behavior. They were especially hostile to the Thistle Long-horned Bees, trying to chase them away by bumping them.
Fortunately, the Thistle Long-horned Bees were undeterred. They were also respectful of other diners, even those smaller than themselves.
I visited this meadow several times within a few weeks, and each time there were at least a half dozen Hummingbird Clearwing Moths at the thistle.
Their close relative, a Snowberry Clearwing Moth, also stopped by for a drink.
One of the Hummingbird Clearwing Moths shared a thistle banquet table with a female Zabulon Skipper, while a male Zabulon Skipper and Peck’s Skipper dined together at another.
These skippers are small butterflies who specialize on various grass species as food for their caterpillars. Many of these grasses can be found nearby in the meadow.
Peck’s Skippers were ubiquitous, sipping nectar alone and in the company of others, including Spicebush Swallowtails and Great-spangled Fritillaries.
Eastern Tiger Swallowtails also visited the flowers for nectar.
All of these large butterflies specialize on plants found in the adjacent woodlands as food for their caterpillars. Spicebush Swallowtails require Spicebush (Lindera benzoin), their namesake plant, or Sassafras (Sassafras albidum); Great-spangled Fritillaries need violets; and Eastern Tiger Swallowtails use various tree species, including Ash (Fraxinus species), Tuliptrees (Liriodendrun tulipifera), and Black Cherry (Prunus serotina).
It was very encouraging to see that there were many Monarch butterflies partaking of the thistle feast. Both Common (Asclepias syriaca) and Swamp Milkweed (Asclepias incarnata) were available in the meadow for egg-laying.
Even Ruby-throated Hummingbirds visited the thistles for nectar, but they didn’t stay long enough for a photo op.
Field Thistle’s strategy to protect itself from being eaten is to have very spiny leaves and branches. This works well in deterring mammals from munching the plant; Field Thistle is not a species that deer are likely to browse. But caterpillars are a different story. Painted Lady butterflies as well as Common Loopers and some other moth species use this plant as food for their caterpillars.
After all of this help with pollination, Field Thistle produces seed-like fruits called achenes. They have a light, white fluff (called pappus) attached, enabling their dispersal by the wind. But these fruits are also desirable food and nesting material for Goldfinches and other birds.
Field Thistle is native from Saskatchewan to Quebec provinces in Canada and in much of the eastern half of the United States, although it is less common in the southeastern states and absent from Florida. The flower color can vary from purple to pinkish, and is occasionally white. Field Thistle is a biennial or short-lived perennial, replacing itself by producing seeds. It can grow to a height of five to seven feet (1.5 – 2.1 meters). Unlike some non-native thistles, Field Thistle is not invasive.
There is a non-native thistle, Bull Thistle (Cirsium vulgare), that closely resembles the native Field Thistle. Some differences in their characteristics that can help tell them apart include: Field Thistle leaves have consistently white felt-like or woolly undersides, Bull Thistle leaves are green to greenish-white below; Bull Thistle has winged stems where the leaves meet them, Field Thistle does not; Field Thistle usually has a ring of leaves pointing upward hugging the base of the inflorescence (flower head), like a very pointy stand-up collar, Bull Thistle may have one or two leaves below the inflorescence.
Field Thistle isn’t traditionally used in gardens, but in the right location in a sunny garden, it could really make a statement, and bring so many visitors!
A Butterfly garden that Embraces the Shade
Black Cherry – for Wildlife and People, Too!
For Great-spangled Fritillaries, Leave the Leaf Litter
Cech, Rick; Tudor, Guy. Butterflies of the East Coast. 2005.
Clemants, Steven; Gracie, Carol. Wildflowers in the Field and Forest. 2006.
Newcomb, Lawrence. Newcomb’s Wildflower Guide. 1977.
Peterson, Roger Tory; McKenny, Margaret. A Field Guide to Wildflowers of Northeastern and Northcentral North America. 1968.
Rhoads, Ann Fowler; Block, Timothy A. The Plants of Pennsylvania. 2007
Invasive Plant Atlas of the United States: Bull Thistle
Mary Anne, Brillant photos and amazing information. I have had the pleasure of going on a walk with you . I believe it was in Bordentown, NJ. You mention in this blog that you took the thistle pics in a local meadow. Where was this meadow? Somewhere in Jersey I assume.
Thank you for sharing your beautiful pics and experiences.
Hi Barbara, nice to hear from you! I’m glad you like the post. The photos were mostly taken at Cedar Ridge Preserve in Hopewell Township, just outside of Hopewell Borough. Here’s more info: http://njtrails.org/trail/cedar-ridge-preserve/. I took the Goldfinch pic at the Pole Farm section of Mercer Meadows, not too far from Cedar Ridge. Hope to see you again!
Dear Mary Anne, I love your posts so very much, and I always share them on French and Pickering Creeks Conservation Trust’s Facebook page. I am afraid to share this one though, as I might be flooded with thistle questions. How do you know that this is not the highly invasive Canada thistle that we are so plagued by here in Chester County? Did you plant this thistle? Even if you planted it, if it reseeds itself, is there any way to identify it when it sprouts? The invasive thistles need to be pulled out as soon as they sprout or they spread like wildfire. Thank you! Your Fan! Donna
Hi Donna, I’m glad you enjoy my posts! All thistles have gotten a bad reputation because of the non-native invasive thistles, but native thistles are beneficial for native wildlife. I was impressed by the number and variety of pollinators visiting the Field thistle flowers. Canada Thistle (Cirsium arvense) is particularly bad. Canada Thistle usually blooms earlier in the summer, usually late June-July. Canada Thistle’s flower heads are much smaller than Field Thistle’s are, about half as high and much narrower, but there may be more of them on each plant. Canada Thistle reproduces through both its seeds and its underground root system, so you are more likely to see it in large colonies. Field Thistle just reproduces through seeds. The bracts that enclose the base of the flower head have spines in Field Thistle, no spines on Canada Thistle. The underside of Field Thistle leaves are consistently felty and white, Canada Thistle leaves are smooth and less white. Field Thistle leaves are very sharply and narrowly lobed, while Canada Thistle leaves are more broadly and irregularly lobed. There’s a video on this link that may also help: https://www.invasivespeciesinfo.gov/plants/canthistle.shtml. Hope that helps!
Really enjoyed seeing all these dining guests..wonderful photos..thank you!
I’m glad you enjoyed the post!
Once again I’ve learned so much! We were just looking at field thistle in the Bowman’s Hill Wildflower Preserve meadow this morning…I wish I had looked long enough to see the thistle long-horned bee! What an interesting array of pollinating visitors this plant has. I’m so happy to know more about this plant. Thank you!
Glad you enjoyed it!
Mary Anne, Thank you again for another of your always superb teaching blogs with its excellent photos. I really learned about the Field Thistle and will add it to my field planting’s next Season.
Valley Head, Alabama
Good decision to add Field Thistle! I’m glad you enjoyed the post.