Trilliums, Flies and Ants

For a few brief weeks in spring, Painted Trillium (Trillium undulatum) opens for business, the business of surviving as an individual plant and reproducing to ensure the continuation of the species.

Painted Trillium (Trillium undulatum)

Trilliums get their name from their structure.  Their leaves and flower parts are in threes or multiples of three.  Each plant has a whorl of three leaves below a single flower that has three petals, three sepals, six anthers, and a three-celled ovary.  ‘Undulatum’ refers to the wavy edges of the flower petals.

Painted Trillium’s three leaves act like solar panels to gather energy from the sun, enabling this plant to produce the carbohydrates it needs to grow and thrive, and to produce flowers that will enable reproduction if the flowers are pollinated.

Painted Trillium (Trillium undulatum)

Painted Trillium flowers have three bright white petals with paint-splatter-like dark red splotches at their base, bleeding into the petal’s veins.  This color contrast is an advertisement designed to attract potential pollinators to visit the flowers, implying that there is nectar and pollen available for a hungry insect to eat.  Painted Trillium offers these rewards because it needs help from a courier to move its pollen to another plant if it is to successfully reproduce through cross pollination.

Fly investigating Painted Trillium (Trillium undulatum), attracted by the dark red nectar guides

There is not a lot of documentation about the likely pollinators for Painted Trillium, but on more than one occasion, I have seen flies visiting the flowers.  The showy display works!  But the flies’ motivation is not to help with pollination.  They have their own needs to meet, mainly finding food.  They may visit the anthers to eat some nutritious pollen,

Fly harvesting pollen from Painted Trillium (Trillium undulatum)

and follow the colorful guides at the throat of the flower, diving deep to look for nectar.

Fly looking for nectar in a Painted Trillium (Trillium undulatum) flower

While foraging on the flower for food, the fly will likely rub its body or legs against the stigmas at the tips of the flower’s female reproductive parts, depositing pollen she may have brought on her body from a previous visit to a Painted Trillium flower.

Fly foraging on a Painted Trillium (Trillium undulatum) flower, with the underside of its abdomen brushing against the stigmas at the tips of the female reproductive parts of the flower. If this Painted Trillium is lucky, the fly will be depositing pollen picked up from another flower.

Fly foraging on a Painted Trillium (Trillium undulatum) flower, with its legs grasping the stigmas at the tips of the female reproductive parts of the flower.

It will also likely rub against the anthers of this flower, picking up pollen to take with it to deposit on the next Painted Trillium flower it visits.

Fly on a Painted Trillium (Trillium undulatum) flower, with its legs brushing against the anthers, from which pollen is dispensed.

Fly on a Painted Trillium (Trillium undulatum) flower, with the underside of its abdomen brushing against the anthers, hopefully picking up some pollen to take to another flower.

This inadvertent pollen transport is what Painted Trillium is counting on.  It has evolved to attract these unwitting pollination partners, and is willing to pay the energy price to reward them in exchange for their assistance with cross-pollination.

Several Trillium species with dark red flowers have evolved to attract flies as their pollinators.  The dark red flower color is often accompanied by a somewhat rank aroma. Together these features are meant to mimic dead rotting flesh (ok, carrion) or other decomposing matter.  Several fly species seek out this kind of material to lay their eggs.  When the larvae emerge from the eggs, they eat the decaying matter, breaking it down and add the result to the soil layer after it passes through the larva’s body.  These insects help crime scene investigators estimate time of death for a corpse, based on the stage and rate of development of the insect in the decaying body.  Many fly species are attracted to the flowers that use this strategy, only to be disappointed when there is no suitable place to lay their eggs.  At least the flies can console themselves with a pollen snack.

Trillium species that use this deceptive strategy include Red Trillium (Trillium erectum), and Toadshade (Trillium sessile, T. cuneatum).

Red Trillium (Trillium erectum)

Red Trillium has many aliases.  It is also known as Purple Trillium, Wake-robin and Stinking Benjamin, this last name a nod to the flowers’ scent, Wake-robin because it blooms at about the same time Robins returned from their wintering grounds, back when they used to migrate more.

Toadshade gets its name from stories of toads taking refuge under the umbrella-like leaves of the plant.

Toadshade (Trillium cuneatum, T.sessile)

In the photo below, a fly is investigating one of the anthers, the source of the flower’s pollen.

Toadshade with fly

If the flower is successfully pollinated, a fruit develops and ripens later in the summer.  The fruit is a berry that splits open when ripe, making its many seeds available for dispersal.  Each seed has an elaiosome attached, a nutritious food packet whose chemical content mimics that of an insect.  This mechanism has evolved to attract ants to disperse the seeds.  It works because ants are omnivorous; they eat some plant material and enjoy sweet treats such as nectar, but insect protein is an important part of their diet.  The ants are attracted to the seeds because of the elaiosome.  They take the seeds back to their homes, eat the elaiosome, and toss the seed on their compost heap, effectively planting the seed in a fertile, protected location.  This evolutionary strategy, known as myrmecochory, is shared by many spring blooming wildflowers.

If you need proof that other insects are important ant food, you’ll find some evidence in the photo below.  I watched while this ant worked tirelessly to drag to its home the moth it’s grasping, working its way across the trail, letting no obstacles like sticks, leaves or rocks deter it from its mission!

Insects are an important source of food for ants. This ant worked tirelessly to drag the moth back to its home.

The elaiosome strategy works in much the same way that fleshy fruits attract birds and other animals to eat their fruits and ‘disperse’ the seeds complete with fertilizer after the seeds pass through the animal’s digestive system, a trait used by many plants that bloom later in the season.

Trilliums typically grow in moist woods.  Painted Trillium is native from Ontario and Quebec south through northern New Jersey and much of Pennsylvania, from there south through the Appalachian mountains to northern Georgia and South Carolina.  It is also present in parts of Michigan.  Red Trillium’s range is a bit broader, from Ontario, Quebec and Michigan, south through northern Alabama, Georgia and South Carolina, with some presence in Indiana and Illinois.  Trillium sessile can be found from western New York state west to Illinois, Missouri and western Kansas, south from Oklahoma to north Carolina.  Trillium cuneatum is native in Pennsylvania, Maryland and Virginia, west to southern Illinois and south from Mississippi to Georgia.

These lovely Trilliums depend on flies and ants for their continued survival.

Painted Trillium (Trillium undulatum)

Related Posts

A Carpet of Spring Beauty, Woven by … Ants!

Resources 

Gracie, Carol.  Spring Wildflowers of the Northeast. 2012.

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

Marshall, Stephen A.  Flies The Natural History and Diversity of Diptera.  2012.

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

Michigan Natural Features Inventory, Trillium undulatum. Willdenow. 2004.

USDA NRCS Plants Database

https://plants.usda.gov/core/profile?symbol=TRUN

https://plants.usda.gov/core/profile?symbol=TRER3

https://plants.usda.gov/core/profile?symbol=TRSE2

https://plants.usda.gov/core/profile?symbol=TRCU

USDA Forest Service Plant of the Week, Painted Trillium (Trillium undulatum), Larry Stritch

 

 

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

 

 

 

Praying for Spring? So is Hobblebush Viburnum

Hobblebush Viburnum (Viburnum lantanoides) in winter

Praying for spring?  Based on appearances, it looks like Hobblebush Viburnum (Viburnum lantanoides, synonym V. alnifolia) is doing the same thing.

Many woody plants can be identified in winter by their distinctive leaf and flower buds, including Hobblebush.  Its leaf ‘buds’ are miniature immature leaves that survive the winter without protective scales.  Since Viburnums have leaves opposite each other along their branches and at branch tips, these leaf ‘buds’ are paired together, a perfect mimic of hands held in prayer.

Hobblebush Viburnum (Viburnum lantanoides) ‘naked’ leaf buds, a term that refers to buds without protective scales.

Where flower buds are present, they nestle between the two leaves in a pair.  In this configuration, the flower buds resemble a moose head, with the leaf ‘buds’ playing the role of moose ears.  That could explain why another common name for this shrub is Moosewood!

Hobblebush Viburnum (Viburnum lantanoides) leaf and flower buds. Do you see the resemblance to a female moose head?

Before the canopy trees have finished leafing out in spring, Hobblebush leaves begin to expand and grow, maximizing their ability to photosynthesize.  At the same time, the flowers also begin to bloom.

Hobblebush Viburnum (Viburnum lantanoides) in spring

Like some hydrangeas, Hobblebush inflorescences have two types of flowers, large sterile flowers around the perimeter of the flower cluster that are incapable of producing fruit, and masses of small fertile flowers in the center.  The sterile flowers open first.

Hobblebush Viburnum (Viburnum lantanoides), with leaves unfurling and sterile flowers blooming. The fertile flowers in the center of the inflorescence are still in bud.

The fertile flowers are where the serious work of pollination takes place.  They open a few at a time over several days, giving the plant a long period during which to lure visitors to help pollinate its flowers. At the same time it’s providing food to those pollinators over many days.  It’s a win-win.

Hobblebush Viburnum (Viburnum lantanoides), with fertile flowers beginning to bloom.

Why would a plant have sterile flowers?  Studies show that there is a higher rate of successful pollination in Hobblebush’s fertile flowers when these showy sterile flowers are present.  The sterile flowers help to advertise the plant’s offerings, luring pollinators to the inflorescence.  The many small fertile flowers make efficient use of the remaining space, offering more chances for the plant to reproduce than would be the case if all of the flowers were as large as those in the outer circle.  Aster family members have evolved a similar strategy.  Many have flower heads with a perimeter of showy but sterile ray flowers surrounding a dense cluster of tiny, tubular, fertile disk flowers.

Hobblebush Viburnum (Viburnum lantanoides) in bloom, with flies foraging on the flowers.

A relatively flat flower cluster like those of Hobblebush Viburnum can accommodate lots of different pollinators, including many bee and fly species.  As an insect moves from flower to flower foraging for food, its body brushes against and picks up pollen from the anthers at the tips of the stamens beneath it. This is an especially effective method of transporting pollen with insects that have hairy bodies to which the pollen can easily adhere.  On the day I observed Hobblebush flowers, flies were the most common visitors.  Flies are important pollinators, especially when the weather is cool; many species are able to fly at lower temperatures than bees.

Hobblebush Viburnum (Viburnum lantanoides) in bloom, with Syrphid fly

If you look closely, you can see that the flies are actually eating the pollen. Many bees and flies harvest both nectar and pollen when they visit flowers.  In addition to eating pollen themselves, female bees gather it to feed their larvae.

Hobblebush Viburnum (Viburnum lantanoides) with Syrphid fly eating pollen. The coloration of this fly mimics a wasp or bee, a disguise to deter predators, but its short antennae identify it as a fly to a discerning eye.

Some butterflies and moths use Hobblebush for food in a different way.  The caterpillars of Spring Azure butterflies and Hummingbird Clearwing moths both eat the leaves or buds of this shrub.

Spring Azure butterfly. Its caterpillars eat the flower buds and leaves of several shrub species, including Hobblebush.

While Hummingbird Clearwing Moths drink nectar from the flowers of many different plants, their caterpillars most frequently eat Viburnum leaves. This mature moth is visiting Swamp Milkweed (Asclepias incarnata) for a quick beverage.

In autumn, Hobblebush leaves turn stunning shades of pink, red and maroon.

Hobblebush Viburnum (Viburnum lantanoides) in fall.

Stunning fall foliage of Hobblebush Viburnum (Viburnum lantanoides)

At the same time the leaves are changing color, the fruit that results from pollinated flowers ripens from green to red, then deepens to a dark blue-black.

Hobblebush Viburnum (Viburnum lantanoides) with ripening fruit

The fruit is a drupe, a fleshy fruit with its seed encased inside in a hard coating.  A peach is an example of a drupe.  Hobblebush fruit is edible for humans, although you may want to avoid those seeds.  Many birds and mammals also eat the fruit, and subsequently ‘disperse’ the seeds, complete with fertilizer.  A few of the animals that eat Hobblebush fruit are pictured below.

American Robin

Northern Cardinal

Hermit Thrush

Eastern Chipmunk

Red Squirrel

In addition to reproducing through its flowers and fruit, Hobblebush can reproduce vegetatively.  Where its branches come in contact with the ground, roots can form and a new shoot can sprout.

Hobblebush Viburnum (Viburnum lantanoides)

Hobblebush Viburnum is a deciduous shrub that can be found in moist woods in Ontario, Quebec, Newfoundland and New Brunswick in Canada, and in the northeastern United States from Maine to northeastern Ohio, south to northern New Jersey and Pennsylvania, and in the Appalachian Mountain region as far south as northeastern Georgia.

Hobblebush is fervent in its belief that spring will eventually arrive.  We should be, too!

Hobblebush Viburnum (Viburnum lantanoides) praying for spring

Related Posts

Asters Yield a Treasure Trove

Nutritious Fall Foliage: What makes leaves so colorful?

Resources

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

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

Peterson, Lee Allen.  A Field Guide to Edible Wild Plants of Eastern and Central North America. 1977.

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

Spira, Timothy A.  Wildflowers & Plant Communities of the Southern Appalachian Mountains & Piedmont.  2011.

Tallamy, Douglas W.  Bringing Nature Home.  2007

Thompson, Elizabeth H.; Sorenson, Eric R.  Wetland, Woodland, Wildland A Guide to the Natural Communities of Vermont.  2005.

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

Adirondacks Forever Wild:  Shrubs of the Adirondacks

Annals of Botany.  Sterile marginal flowers increase visitation and fruit set in the hobblebush (Viburnum lantanoides, Adoxaceae) at multiple spatial scales.

Biology Discussion

USDA NRCS Plants Database

 

 

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