Hackberry, Butterflies and Birds

Common Hackberry (Celtis occidentalis) is a tree whose ridged, warty bark makes it easy to recognize in any season.  It may be easiest to spot in winter, since there are fewer leaves to distract from Hackberry’s distinctive outerwear.

Common Hackberry (Celtis occidentalis)

Look for Hackberry on a winter day that’s a little warmer than normal, and you might be rewarded with a glimpse of one of the butterflies that are among Hackberry’s known associates, the Mourning Cloak and the Question Mark.

Mourning Cloak butterfly

Question Mark butterfly. It is named for the white markings on its wing.

Both of these butterflies survive the winter as adults, spending most of the time sheltering in dry accommodations such as under loose bark, in a woodpile, or in a crevice or hole in a tree.  The butterflies are able to produce an anti-freeze-like substance that keeps them from succumbing to the winter cold.  They are mostly inactive during the winter; they rarely eat and don’t reproduce.  But they may venture out on a warmish winter day to look for a snack of minerals from rotting fruit, dung, sap or mud puddles.  When you are a butterfly that wakes up from a winter nap in northern latitudes, you have to have a flexible diet.  Not many flowers are blooming to offer nectar during the cold winter months.

While these butterflies may be found anywhere in the woods, in the warmer months when reproduction is on their mind, they are known to associate with Hackberry trees because they are one of the species whose leaves the caterpillars of both these butterflies can eat.  In addition to Hackberries, Mourning Cloak caterpillars use the leaves of a variety of trees, including willows, elms, birch, cottonwoods and aspen.  Question Mark caterpillars can also eat elm tree and nettle leaves.

Question Mark caterpillar on Hackberry leaves

In the spring and summer months, you may see additional butterflies whose caterpillars specialize on Hackberry leaves.  These species depend solely on Hackberries for their survival.  They include the curious looking and aptly named American Snout, the Tawny Emperor, and Hackberry Emperor.

American Snout butterfly drinking nectar from Short-toothed Mountain Mint (Pycnanthemum muticum)

The American Snout drinks nectar in addition to seeking out minerals.  Its long ‘nose’ is thought to have evolved to look like the stem of a leaf, which together with the cryptic coloration of its wings helps this butterfly to hide in plain sight, disguised as a dead leaf.

Tawny Emperor

Hackberry Emperor

Because Tawny and Hackberry Emperors rarely nectar, you are most likely to encounter them in or near wooded areas where their caterpillar food is present.  Their diet of minerals from mud, sap, and rotting materials such as fruit and dung is similar to that of the Mourning Cloak and Question Mark.  Hackberry Emperors also find human sweat to be a good nutritional source.  It is the species of butterfly I have most often seen landing on people to get a quick snack!

Hackberry Emperor getting minerals from soil and rocks.

Hackberry Emperor getting minerals from the sweat on someone’s shirt!

Hackberry Emperor getting minerals from the hood of a car. Is it the paint or the dirt?

Not every caterpillar will live to become an adult butterfly, since there are many predators to elude first.  The Hackberry Emperor caterpillar in the photo below has fallen victim to a parasitic wasp. Her larva will develop inside the caterpillar, consuming its insides until the wasp is mature enough to emerge.  As you might expect, the caterpillar is unlikely to survive.

Hackberry Emperor caterpillar, with a predatory wasp.

Several moth species including the IO Moth, and White-marked and Banded Tussock Moths also use Hackberries, among other woody species, as food for their caterpillars.

White-marked Tussock Moth

Banded Tussock Moth

The round growths on the leaves in the photo below are galls called Hackberry Nipple Galls.  They are caused by a type of true bug in a group called psyllids, or less appealingly, jumping plant lice.  The insects develop inside the galls and emerge when they mature.

Common Hackberry with ripening fruit and Hackberry Nipple Galls, caused by Pachypsylla celtidismamma.

Many of these insects are a potential bounty of food for birds.  I watched the young Tufted Titmouse below and its nest mates forage for food and play among the branches of a mature Hackberry.

Tufted Titmouse in Hackberry

Hackberry’s somewhat inconspicuous flowers are pollinated by the wind, blooming at the same time that the leaves are beginning to emerge.  Hackberries are monoecious; they have some flowers with just male reproductive parts, others with just female flowers, with both types of flowers on the same trees.  In the photo below, both male and female flowers are present.  The female flowers have two stigma-tipped styles that are spread in a ‘v’ shape projecting from the flower. (They look like forceps, or they also remind me of the arcade games where you have to use a similar looking tool to retrieve a toy from a glass enclosure.)  The male flowers have five or six anther-tipped stamens that barely project beyond the enclosing sepals.  A tree may even have some flowers with both male and female parts.  Pollen is carried by the wind from the anthers and deposited on the stigmas.

Common Hackberry (Celtis occidentalis) flowers. The female flowers have 2 styles spread in a ‘v’ shape. The male flowers each have 5-6 dark-colored anthers.

If the flowers are pollinated, a fruit called a drupe is produced.  A drupe is a fleshy fruit that has a stony enclosure around the seed inside, like a peach.  The fruit ripens in fall, but may persist into winter. Birds as diverse as Mockingbirds,

Mockingbird

Pileated Woodpeckers,

Pileated Woodpecker

and Wood Ducks eat Hackberry fruit.

A pair of Wood Ducks

Raccoons and squirrels are among the small mammals who eat the fruit.

A raccoon peaking out from its home.

Common Hackberry’s natural habitat includes wooded floodplains and hillsides, and can grow to a height of about 115 feet (35 meters).  It is native in Manitoba, Ontario and Quebec provinces in Canada and most of the United States, from New Hampshire to Montana in the north, south through Utah, New Mexico and east to Florida, except Louisiana, although it is less common in the southern part of its range.   It is also often used as a street tree.

There is a related species, Sugarberry (C. laevigata) that is native in the southern half of the United States and in the western states.  Dwarf Hackberry (Celtis pumila) is native in Ontario, Michigan, and from New Jersey west to Kansas, and south from Texas to Florida.  The butterflies that specialize on Hackberries use these species, too!

Common Hackberry (Celtis occidentalis)

Resources

Allen, Thomas J.; Brock, Jim P.; Glassberg, Jeffrey. Caterpillars in the Field and Garden. 2005.

Cech, Rick; Tudor, Guy.  Butterflies of the East Coast.  2005.

Eastman, John.  The Book of Forest and Thicket.  1992.

Eaton, Eric R.; Kauffman, Ken.  Kaufman Field Guide to Insects of North America.  2007.

Eiseman, Charley; Charney, Noah.  Tracks & Sign of Insects and Other Invertebrates.  2010.

Martin, Alexander C.;  Zim, Herbert S.; Nelson, Arnold L.  American Wildlife & Plants A Guide to Wildlife Food Habits.  1951.

Rhoads, Ann Fowler; Block, Timothy A.  The Plants of Pennsylvania.  2007

Tallamy, Douglas W.  Bringing Nature Home.  2007

Wagner, David L.;  Caterpillars of Eastern North America, 2005.

Illinois Wildflowers
http://www.illinoiswildflowers.info/trees/plants/hackberry.html
http://www.illinoiswildflowers.info/trees/tables/table153.html

USDA NRCS Plant Database
https://plants.usda.gov/core/profile?symbol=CEOC
https://plants.usda.gov/plantguide/pdf/pg_ceoc.pdf

USDA US Forest Service

Oregon State University College of Agricultural Sciences Department of Horticulture Landscape Plants

 

 

 

A Pledge for the New Year

Song Sparrow with caterpillar (lunch!) surrounded by ripening fruit in a Black Cherry (Prunus serotina) tree.

For the new year and beyond, I pledge to do all I can to help achieve a healthy, diverse world, including reducing fossil fuel usage, and using more plants that are native to the area where I live.

I hope you’ll join me!

 

Oaks Have a Lot of Gall!

In late fall and early winter, oak (Quercus species) trees often stand out from their forest companions, refusing to let go of their richly colored russet and brown leaves long after other deciduous trees are completely bare.  Oaks are members of the Beech (Fagaceae) family, and winter leaf retention, or marcescence, is a family trait.  American Beech (Fagus grandifolia) trees tenaciously hold their leaves until early spring when new leaves are preparing to emerge.

Oak trees, retaining their leaves, stand out in a woodland in late fall.

No one knows exactly why some deciduous trees exhibit this characteristic, but there are several theories.  It may be that the dry leaves are a deterrent to winter browsing by deer, moose and other mammals.  Holding on to leaves until spring may be the trees’ way of time-releasing nutrients for recycling into the soil.  Or the leaves may capture and funnel more snow melt to the tree’s root system.

There are about 600 species of oaks (Quercus) worldwide, with 87 in North America, as well as numerous hybrids.  Oaks are usually categorized in two groups, the white oak group and the red oak group.  They can be distinguished by their leaves.  Trees in the white oak group have leaves with rounded lobes,

White Oak (Quercus alba)

while trees in the red oak group have leaves with pointed lobes or with very narrow ‘pins’ at the tips of their lobes.

Red Oak (Quercus rubra)

Oaks are among the most valuable species for supporting both wildlife and people, in many different ways.

The wind-pollinated flowers of oaks produce acorns, an important food for wildlife.

Acorn of Swamp White Oak (Quercus bicolor)

Many birds depend on this bounty of food, including Jays, Tufted Titmice, Red-headed and Red-bellied Woodpeckers, Ruffed Grouse, Lesser Prairie Chickens, Bobwhite and other quails, and Wild Turkeys.

Red-bellied Woodpeckers are among the many birds that eat acorns.

White-breasted Nuthatches are most often seen foraging for food, mostly insects, in the crevices of tree bark, but they also like fruit, and are named for their habit of tucking seeds and nuts like acorns into a crevice and hacking away at them to consume the tasty treat inside.  They may also cache some acorns for later consumption.

White-Breasted Nuthatch

Even Wood Ducks consume acorns.  They primarily live in forested wetlands where oak trees and acorns may be present. Wood Ducks are just one of the many animals that nest in tree cavities such as those found in oaks.

Wood Duck in fall

Acorns are an important food source for many mammals, from mice, chipmunks, raccoons and squirrels, to bear and deer.

Raccoons are among the many mammals that eat acorns, and may find shelter in oak or other tree cavities.

Eastern Gray Squirrels have a special relationship with oaks.  Not only do they consume acorns and shelter in oak cavities, but in return they help to disperse oak seeds (acorns).  Like the White-breasted Nuthatches, Gray Squirrels cache acorns for later consumption.  Squirrels typically have a very good memory for where they stashed each acorn, often recovering as much as 95% of their hoard.  But the other overlooked 5% may germinate and prosper in their new location.  Oaks also tend to have ‘mast years’ when they produce more acorns than can be easily eaten even over the long winter.  In such years, many acorns may live to become trees.

Eastern Gray Squirrel

Acorns are at their most nutritious before they germinate.  Acorns of trees in the white oak group germinate in their first year.  Squirrels can detect this, and are likely to eat acorns from the white oak group as soon as they are available rather than cache them.  Trees in the red oak group produce acorns that take two years to germinate.  Squirrels are likely to cache acorns from trees in the red oak group, since they remain a viable food source for a longer period of time.

When acorns are plentiful, Gray Squirrels, Blue Jays, White-footed Mice and other acorn consumers tend to eat only about half of each acorn, the half at the opposite end from which the tree seedling will emerge (the end without the ‘cap’).  This part of the acorn has a higher lipid content, the food these animals are seeking, and a lower tannin content, a bitter tasting compound that is off-putting to potential consumers.  The discarded uneaten half acorn will often germinate and produce a seedling.

Studies have shown that in the mid-Atlantic United States, oaks are food plants for the caterpillars of more butterfly and moth species than any other genus of trees, supporting more than 500 species.

Juvenal’s Duskywing nectaring from Spring Beauty (Claytonia virginica). Several Duskywing butterfly species use oaks as caterpillar food.

Red-banded Hairstreaks use the fallen leaves of oaks and sumacs as caterpillar food. The spend the winter in the fallen leaves.

Saddleback moth caterpillars eat oak leaves

Several giant silk moths like this Polyphemous Moth and Luna Moths depend on oaks for caterpillar food.

Insects, and especially caterpillars, are an important source of food for birds and other animals.  It takes thousands of caterpillars to feed a young bird family.  As a result, many of those caterpillars will become a meal before they get a chance to become a butterfly or moth.

Carolina Chickadees need thousands of caterpillars to raise a single brood.

Carolina Wrens need food in the form of the many caterpillars and other insects found on oak trees.

There are other insects whose presence in oak tissue stimulates the oak to produce a gall, an abnormal plant growth with more nutrients than are found in normal tissue.  The insect develops inside the gall, feeding on the nutrient rich tissue inside.  Some oak galls are caused by midges, but many are caused by members of a sub-family of wasps called gall (Cynipid) wasps.  The galls take some of the plant’s resources, but they typically don’t cause any harm to the plant.  Often these galls house additional insects, free-loaders (inquilines) that didn’t stimulate the tree to produce the gall but who live and feed in the gall, sharing it with the original tenant.

The galls on these Pin Oak (Quercus palustris) leaves are caused by a midge, Polystepha pilulae.

This gall on Swamp White Oak (Quercus bicolor) is called a Lobed or Pine Cone Oak Gall. It is caused by a wasp.

This summer my attention was drawn to a Swamp White Oak (Quercus bicolor)  branch by ants rapidly climbing around on several ‘bumps’ that could only be galls.  At this point the galls were somewhat nondescript little growths that turned out to be Oak Bullet Galls.

Ants patrolling galls on Swamp White Oak (Quercus bicolor)

But what attracted the ants to the galls?  Ants are omnivorous. Other insects are important food for them, but they also eat plant material and sweet tasty treats, like nectar.  Since they didn’t have access to the insects inside the galls, I speculated that there was something on the exterior of the gall that enticed them.  When I looked at my photos, they did appear to be eating something, but what?

Ants with Oak Bullet Galls galls on Swamp White Oak (Quercus bicolor)

When I checked on the galls about a week later, their appearance had changed dramatically; they now looked like red Hershey’s Kisses.  The ants were still on duty, and this time when I checked my photos, I could see droplets of nectar oozing out from the sides of the galls.  Mystery solved!  The wasp inside the gall had stimulated the tree to not only produce its home and food, but the home came equipped with a security system – nectaries to lure and pay for protection from predators.

Ant drinking nectar from Oak Bullet Gall on Swamp White Oak (Quercus bicolor). The glistening nectar droplets are especially visible just below the tip of the ant’s right front leg.

My next visit was about two weeks after the Hershey’s Kisses phase of the gall development.  Their appearance had changed again; now each gall had a tan, almost perfectly round exterior.  This time the ants were joined on patrol by several wasp species, each capable of discouraging predators of the gall wasp.

Paper Wasp drinking nectar from Oak Bullet Gall on Swamp White Oak (Quercus bicolor).

Cuckoo Wasp drinking nectar from Oak Bullet Gall on Swamp White Oak (Quercus bicolor).

This seems like an expensive security service for the tree to provide if it only benefits the gall wasp.  It is likely that many of these insect guards also protect the tree itself from other herbivores.  For example, Paper Wasps, like ants, are caterpillar predators.

Oaks also have relationships with many fungi, including species that are edible or provide medicine for humans, insects and other animals.

Hen of the Wood is just one of the many fungi that have a relationship with oak trees.

There is a plant called Squawroot or Cancer-root (Conopholis americana) that depends on oaks for its survival.  Squawroot doesn’t produce its own food through photosynthesis. Instead it taps into the roots of oak trees for its food.

Squawroot or Cancer-root (Conopholis americana)

How are oak trees beneficial for people?   If prepared correctly, some acorns are edible.  The wood is used for building, furniture and cabinet making.  The bark of some species is used for tanning.  Oak trees, especially the inner bark, have numerous medicinal uses.  Most importantly, through photosynthesis, oak trees and other plants produce the oxygen we need in order to breathe.  They help mitigate climate change by removing carbon dioxide and other pollutants from our air and water, providing cooling shade, producing moisture through transpiration, and helping to manage stormwater.

Swamp White Oak (Quercus bicolor)

Not only do oaks have a lot of gall, but they provide immeasurable value to life on earth.

Oak trees stand out in a woodland in late fall

Related Posts

Will Work for Food – Extra-floral Nectaries

American Beech

Resources

Beresford-Kroeger, Diana.  Arboretum America: A Philosophy of the Forest.  2003

Cech, Rick; Tudor, Guy.  Butterflies of the East Coast.  2005.

Eastman, John.  Birds of Forest, Yard, & Thicket.  1997.

Eastman, John.  Birds of Lake, Pond and Marsh.  1999.

Eastman, John.  The Book of Forest and Thicket.  1992.

Eastman, John.  The Book of Swamp and Bog.  1995.

Eaton, Eric R.; Kauffman, Ken.  Kaufman Field Guide to Insects of North America.  2007.

Eiseman, Charley; Charney, Noah.  Tracks & Sign of Insects and Other Invertebrates.  2010.

Martin, Alexander C.;  Zim, Herbert S.; Nelson, Arnold L.  American Wildlife & Plants A Guide to Wildlife Food Habits.  1951.

Nelson, Gil; Earle, Christopher J.; Spellenberg, Richard.  Trees of Eastern North America.  2014.

Sibley, David Allen.  The Sibley Guide to Bird Life and Behavior.  2001.

Steele, Michael A.; Koprowski, John L.  North American Tree Squirrels.  2001.

Tallamy, Douglas W.  Bringing Nature Home.  2007

Wagner, David L.;  Caterpillars of Eastern North America, 2005.

Buckeye Yard and Garden Online: Bullet Galls and Their Guards by Joe Boggs, October 2018

Capital Naturalist by Alonso Abugattas

Illinois Wildflowers

Minnesotaseasons.com

Missouri Botanical Garden

Naturalis Historia

Penn State College of Agricultural Sciences, Winter Leaves That Hang On

 

 

Virginia Creeper is for the Birds!

Virginia Creeper (Parthenocissus quinquefolia) is at its showiest in autumn.  The leaves of this native vine turn bright scarlet, a perfect offset for its ripening fruit. It’s especially striking where it has found a platform to climb.

Virginia Creeper (Parthenocissus quinquefolia)

Virginia Creeper is typically found in woodlands, wood’s edges and fields. It grows as a ground cover,

Virginia Creeper (Parthenocissus quinquefolia) in center forefront. It is a welcome addition to the groundcover in my shade garden, and seems to work and play well with other plants.

but can also climb trees

Virginia Creeper (Parthenocissus quinquefolia)

and fences or arbors.

Virginia Creeper (Parthenocissus quinquefolia) on a fence

It climbs in a gentle way, using its tendrils.  the tips of the tendrils form a suction cup-like pad at their tips that can cling to bark, fences and arbors.

Where Virginia Creeper gets enough sun it will flower, typically in mid-summer.

Virginia Creeper (Parthenocissus quinquefolia) in bloom

The flowers offer nectar and pollen that are attractive to many bee species.  If the bees are successful in assisting Virginia Creeper with pollination, berries develop and ripen in late summer and fall.

Virginia Creeper (Parthenocissus quinquefolia) fruit

At the same time that Virginia Creeper’s leaves are changing color, its fruit stems (petioles) also turn scarlet, a striking contrast to the fruit that ripens to a deep blue.  This colorful display is an advertisement that attracts birds to feast on the luscious fruit.  Virginia Creeper has evolved to attract animals to eat its fruit and subsequently disperse its seeds.   The seeds go through the animal’s digestive tract, and are eventually deposited complete with natural fertilizer in another location.

Birds including Woodpeckers, Titmice, Chickadees, White-breasted Nuthatches, Thrushes, Robins, Catbirds and more flock to this autumn food source.  On a recent fall day, I watched Eastern Bluebirds, Cedar Waxwings and several sparrows taking advantage of Virginia Creeper’s bounty.

Eastern Bluebirds foraging for fruit from Virginia Creeper (Parthenocissus quinquefolia)

A Cedar Waxwing and an Eastern Bluebird eating Virginia Creeper (Parthenocissus quinquefolia) fruit

Because of its habitat, habit of climbing, and color, Virginia Creeper is sometimes mistaken for Poison Ivy (Toxicodendron radicans), but they are easy to tell apart.  Poison Ivy has compound leaves with three leaflets, while Virginia Creeper’s compound leaves have five leaflets, reflected in its scientific name, ‘quinquefolia’, which means five-leaved.

Virginia Creeper (Parthenocissus quinquefolia) has compound leaves, usually with five leaflets

Mature Poison Ivy vines have very hairy stems, while Virginia Creeper’s bark is not hairy.  Virginia Creeper has exfoliating bark typical of other members of its family, the Grape (Vitaceae) family.  The bark may be used by birds for nesting material.

Virginia Creeper has other characteristics in common with its family members.  For example, its fruit clusters may resemble a bunch of grapes.

Virginia Creeper (Parthenocissus quinquefolia) fruit clusters may resemble those of other Grape family members.

Virginia Creeper is also a food plant for the caterpillars of several moth species that specialize on grape family members.  Among them are the regal-looking Eight-spotted Forester,

Eight-Spotted Forrester on Virginia Creeper (Parthenocissus quinquefolia)

and the Grape-leaf Skeletonizer.

Grapeleaf Skeletonizer on New Jersey Tea (Ceanothus americanus). This moth drinks nectar from many plants, but its caterpillars can only eat the leaves of Grape family members.

The caterpillars may successfully complete metamorphosis, or they may become food for resident birds or other wildlife.  Insects, especially caterpillars, are an important source of food for birds.

Tufted Titmice are just one of the many species of birds that may benefit by eating the caterpillars found on Virginia Creeper.

Virginia Creeper is also known by the common name Woodbine.  It is native in the eastern two-thirds of the United States and Canada.

At different times of the year Virginia Creeper provides fruit, caterpillars, and nesting material.  Its dense leafy cover can also be a good place to take shelter.  What more could a bird ask for?

Virginia Creeper (Parthenocissus quinquefolia) with Eastern Bluebird

Resources

Rhoads, Ann Fowler; Block, Timothy A.  The Plants of Pennsylvania.  2007

Stearn, William T. Stearn’s Dictionary of Plant Names.  1996

Audubon – 10 Plants for a Bird-friendly Yard

Illinois Wildflowers

 

University of Connecticut College of Agriculture, Health and Natural Resources Plant Database

USDA NRCS Plant Database

 

 

A Thistle Banquet

On a recent walk through a local meadow I spotted a bank of Field Thistle (Cirsium discolor).

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.

A Honey Bee, a Thistle Long-horned Bee (Melissodes desponsus) and a Hummingbird Clearwing Moth all drinking nectar from Field Thistle (Cirsium discolor)

At another, several Bumble Bees, Honey Bees and Thistle Long-horned Bees shared a meal.

Bumble Bees, Honey Bees and a Thistle Long-horned Bee (Melissodes desponsus) feeding from Field Thistle (Cirsium discolor)

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.

Field Thistle (Cirsium discolor). Note the individual narrow, trumpet-like disk flowers shown below the bee.

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.

Thistle Long-horned Bee (Melissodes desponsus) feeding on Field Thistle (Cirsium discolor). She’ll bring the pollen on her hind legs to her nest. Note the pollen grains all over her body! Some will help with pollination.

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.

Honey Bee bullying Thistle Long-horned Bee (Melissodes desponsus) on Field Thistle (Cirsium discolor).

Fortunately, the Thistle Long-horned Bees were undeterred.  They were also respectful of other diners, even those smaller than themselves.

The small bee (possible Eucera species) in the upper left is harvesting pollen. With Thistle Long-horned Bee (Melissodes desponsus) on Field Thistle (Cirsium discolor).

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.

Hummingbird Clearwing Moths on Field Thistle (Cirsium discolor).

Their close relative, a Snowberry Clearwing Moth, also stopped by for a drink.

Snowberry Clearwing Moth drinking nectar from Field Thistle (Cirsium discolor).

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.

Female Zabulon Skipper and Hummingbird Clearwing Moth drinking nectar from Field Thistle (Cirsium discolor).

Male Zabulon Skipper (left) and Peck’s Skipper drinking nectar from Field Thistle (Cirsium discolor).

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 Skipper drinking nectar from Field Thistle (Cirsium discolor).

Peck’s Skippers were ubiquitous, sipping nectar alone and in the company of others, including Spicebush Swallowtails and Great-spangled Fritillaries.

Spicebush Swallowtail and Peck’s Skipper drinking nectar from Field Thistle (Cirsium discolor).

Two courting Great-spangled Fritillaries and Peck’s Skipper on Field Thistle (Cirsium discolor).

Eastern Tiger Swallowtails also visited the flowers for nectar.

Eastern Tiger Swallowtail drinking nectar from Field Thistle (Cirsium discolor).

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.

Monarch butterfly drinking nectar from Field Thistle (Cirsium discolor).

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.

Painted Lady on White Snakeroot (Ageratina altissima). Field Thistle (Cirsium discolor) is one of the plant species that Painted Lady butterflies can use as food for their caterpillars.

Common Looper Moth on New England Aster ( Symphyotrichum novae-angliae). Common Looper Moths caterpillars also eat the leaves of Field thistle (Cirsium discolor).

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.

Eastern Goldflinches harvesting seeds from Field thistle (Cirsium discolor)

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 (Cirsium discolor) with great-spangled Fritillary butterfly. Note the stand-up leaf collar hugging the base of the flower head.

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!

Field Thistle (Cirsium discolor)

 

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Resources

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

Illinois Wildflowers

Invasive Plant Atlas of the United States: Bull Thistle

USDA NRCS Plant Database

USDA NRCS Plant Fact Sheet