Monthly Archives: July 2018

Invasive Species Spotlight: English Ivy

DSC_0008It is often described as a lovely, evergreen groundcover. It is also a damaging, invasive species.

English ivy is widely planted, probably ever since ornamental plants were first imported to the United States. Because it is a ground-covering vine that smothers anything in its path, English ivy has been linked to the loss of plant diversity. Winter is the time of year that Hedera helix, or English ivy, makes its presence known. It stays green all year, which is probably one of the reasons why county residents like it in their yards or climbing their mailboxes. English ivy also stands out in natural areas during winter and often is the only green in the forest after native plants have died back for the year.

DSC_0010English ivy is especially dangerous to trees. Once the vine reaches branches, its extra weight can cause those branches to break, injuring the tree and opening an entry point for pathogens or fungus infections. Even if the tree can manage the extra weight from the vines, English ivy will eventually cover all the branches, shading leaves and leading to the tree’s death. English ivy growing on private property can spread to natural areas where it can grow unchecked.

DSCN1481Invasive species are widely considered to be the second-worst cause of ecosystem function degradation. The first is habitat loss, however, invasive species and habitat loss often go hand in hand. To learn more about invasive species removal in Fairfax County parks, visit the Invasive Management Area (IMA) website. IMA has 60 habitat restoration sites around the county, and the Park Authority is always looking for additional IMA volunteers.

Healthy ecosystems provide better air quality, better water quality, more opportunities for wildlife, and plant diversity. All of that means more opportunities for us to discover new things in our natural world. In Fairfax County, with less than 10% of the land protected in natural areas, it is even more important that our natural areas function as best they can.

English Ivy 2, Mail PostTake time to assess the area around your house. Can you spot English ivy creeping up trees or mailboxes, or did you plant English ivy in your yard? We have suggestions on our website for replacement plants.

Learn more about English ivy in this online field guide and more about invasive plants in this online discussion archive. Our colleagues in King County, Washington, also have an excellent web page with information about English ivy.

Remove English ivy and replant with a mix of native ground covers like ferns, spring beauty, Dutchman’s breeches and trillium. The native plants will be a much more interesting bunch — and not invasive.

This blog was compiled from Park Authority files and edited by Park Authority Ecologist Erin Stockschlaeder.


Caterpillars are Taking off Their Skeletons at Hidden Oaks!

DSC_0268The race is on to see who will become a butterfly or moth first. There are Monarchs, Pipevine Swallowtail, and Tobacco Hornworm caterpillars at Hidden Oaks Nature Center in Annandale.

If you happen to visit at the right time, you may see the Monarchs and Pipevine Swallowtail butterflies being released. The Tobacco Hornworm moths will be kept at the nature center to exhibit as adults.


A natural wonder that typically enjoys great favor with humans, the monarch butterfly makes headlines across North America. As an ambassador insect, or one that represents a genre such as pollinators, these insects often are used to teach about life cycles. Ask any second grader, and she will tell you about the struggles of this tenacious insect that depends on one plant, milkweed, for survival.

As wild milkweed decreases, national organizations and neighborhood nature centers encourage people to plant milkweed varieties to support monarchs and other pollinators. With their widespread popularity, it’s no surprise children delight in observing monarch caterpillars being raised at Hidden Oaks.

monarch cat.-aHidden Oaks has championed monarch butterfly awareness and stewardship since 1996. Monarchs usually do not arrive in the Washington area before July, and this year the first batch arrived at the nature center on July 9. Journey North, an online science education project, records the first spotting of monarch eggs throughout the country. Normally, the D.C. area spots monarch eggs on milkweed after June 20. Recently, the date has been creeping earlier on the calendar, with this year’s mid-April sighting the earliest on record. The earlier arrivals may be due to warmer weather and a reduction of milkweed in wintering habitats.

Monarch 2017-aOften the monarchs winging their way through the D.C. area are the last of four generations produced over a calendar year. The last generation is physiologically different from the previous three. The last generation does not typically have the benefit of fresh milkweed and is generally in a nonproductive mode until after their diapause, or overwintering, in Mexico. The previous three generations, which can mate within a week of emerging from their chrysalids, have a life span of about six weeks. The fourth generation, which can live six to eight months, mates after spending months resting – with millions of other monarchs – in the Transvolcanic Mountain range about 60 miles northwest of Mexico City.

More about monarchs

Pipevine Swallowtail

The pipevine swallowtail begins life as a small, black and red caterpillar. This caterpillar has a strict diet, but is a little more flexible than the monarch. It feeds on many varieties of plants in the Aristolochiaceae family, commonly known as the pipevine family of plants. Aside from being delicious for the caterpillar, these plants also contain a toxin that is harmful to many animals, but the pipevine swallowtail is an exception. The caterpillars use this to their advantage and incorporate the toxin into their body where it becomes a defense against predators.

The toxin stays in the caterpillars’ bodies as they go through metamorphosis and turn into butterflies. When the butterflies are old enough to lay eggs, they choose the pipevine plant as their landing pad. This provides some protection to the eggs and ensures that they have something to eat the moment they hatch. Once they hatch, the young larvae remain together and feed as a group. This defense strategy confuses predators, since a group of caterpillars may look like too big of a bite. Once they are older and their bodies possess warning signs of bright orange spikes, they split from the group and feed alone. Pipevine swallowtails are found from the northeastern United States south and west to New Mexico and Arizona as well as in parts of California.

More about swallowtails

Tobacco Hornworm

Hornworms at WRTobacco Hornworm caterpillars are rather striking in appearance, starting out almost translucent, turning bright aqua blue, and then altering to a bright green with white stripes. The caterpillar also has a red “horn” at the posterior end. The caterpillars grow rapidly, starting at around a half-inch and growing to about three and a-quarter inches.

They grow this big because they voraciously munch on tomato plants, much to the dismay of farmers and gardeners. Although tomatoes are their preferred food, they will eat anything in the family Solanaceae, which includes tobacco, pepper, eggplant, and various ornamentals and weeds. The tobacco hornworms at Hidden Oaks have munched through many of the tomato plants, sometimes in as little as a day. After they’ve eaten their fill, they are ready to become moths.

hornwormsWhile the monarch butterfly hangs from a leaf or branch to create its chrysalis, the tobacco hornworm moth forms a pupal cell below the leaf litter or just under the top layer of soil. It is a dark reddish-brown, with a maxillary loop at the anterior (front) end and a pointed posterior (rear) end. Sometimes these pupae can spend an entire winter underground, with the moth emerging in the spring.

Once they have gone through metamorphosis, the adult moth emerges. The wings are mottled black, brown, and white, and fold under in a triangular manner to help provide camouflage. The hornworm is sometimes called a hummingbird moth due to its tendency to fly nimbly among flowers and hover over them to extract nectar with their proboscis.

More about tobacco hornworm

Visit Hidden Oaks to pick up a free packet of native swamp milkweed seeds to attract butterflies and other pollinators to your backyard or school. Share the joy and wonder with your family and friends by experiencing first-hand the variety of native butterflies, and marvel at the mysteries of caterpillars that scientists have yet to completely unravel.

Author Fiona Davies is the Volunteer Coordinator at Hidden Oaks Nature Center.

Sources: University of Florida, Grow Garden Tomatoes, Butterflies and Moths of North America, and GotScience Magazine.

Treat Yourself by Treating Birds

DSC_7043_edited-2The U.S. Fish and Wildlife Service estimates more than 50 million people in North America feed birds. If you are one of them, you know the rewards. It’s fun!

Bird-4Many Fairfax County residents enjoy luring the color, song and antics of year-round and migrating high-flying inhabitants of the bird world, and a backyard bird feeder is a prime way to do that. Some folks provide seed only during winter with the hope of sustaining resident species, and others opt to feed all year.

By feeding through spring and summer, homeowners witness the joys and tribulations of avian child-rearing. Human parents watch their feathered counterparts fret over when junior will take that first successful flight. In fact, the human interest factor is likely the major benefit of backyard bird feeding.

DSC_3034_edited-2By enticing certain species to their yards, county residents develop an understanding of and appreciation for local birds. A simple scattering of mixed birdseed will attract several species that enjoy feeding on the ground. Families can easily distinguish among the redbirds, doves and the little brown sparrows that descend. Interest grows, and someone makes an effort to learn the names of those Northern cardinals, mourning doves, English sparrows and Carolina wrens.

There are several types of feeders, and they attract different species. Platform feeders encourage mourning doves and blue jays. Keeping the seed off the ground discourages rodents from visiting, but squirrels have a grand time enjoying their fill. Tube feeders have openings that attract perching birds from cardinals to sparrows. The finch feeders with tiny openings accommodate only smaller-billed birds, including house finches and the beautiful goldfinches.

The secret to attracting the birds you want to your yard while discouraging others such as crows or starlings is to provide the preferred seed. Insect eaters gravitate toward protein substitutes such as black oil sunflower seed and suet (beef fat). Suet, available at the meat counter at grocery stores, is less attractive to crows and squirrels when it has no added seed. Cardinals dote on safflower seed, and finches flock to niger-thistle seed in tube feeders.

DSC_2971Homeowners’ number-one complaint about feeding birds is the abundance of squirrels and other rodents attracted by the seeds. Squirrels typically find safflower seed distasteful and may opt to dine elsewhere if they find it mixed with the tempting sunflower seeds. Another option is setting up a separate feeding station of corn and peanuts. Specialty wildlife stores sell squirrel-proof feeders that boast a trap door that shuts out heavier animals, such as crows and squirrels. Sometimes they even work – until the squirrels figure out how to beat the system. Watching squirrels during their trial-and-error can be part of the fun.

A metal case with a locked lid will provide more hours of viewing pleasure than a mesh onion bag. A secured cage on a stable surface will draw the attention of red-bellied, downy, hairy and possibly even pileated woodpeckers plus skittish Carolina chickadees and white-breasted nuthatches. Exclusion feeders or baffles, metal cones over the tops of tube feeders, can help. Squirrels and raccoons will make a quick getaway with anything not firmly attached to a tree or post.

Our videos, Night Thief and Pole Climber, will give you an idea of the skill and determination critters have to get your bird seed.

A quick trip to your local nature center, library or wildlife supply store can provide guidelines for the heights of feeders and distance recommended from trees. To minimize visits from rats and mice, put out only the amount of seed eaten in a day. Spilled seed on the ground not only attracts rodents but can be a health hazard to birds if it molds. Sunflower seed hulls contain a toxin that prevents some plants from sprouting or developing deep roots. You could buy more expensive shelled seed, use a seed tray under the feeder, experiment with plants such as daylilies, tickseed or coneflower under the feeder, rake or vacuum the seed hulls, build a bird feeder patio, or just have a bare spot.

DSC_7802_edited-3Assuring the health of your feathered guests requires regular maintenance. A commonly overlooked component of backyard feeding is a clean, pure water source. Bird mites and other microscopic critters living on birds and dust contaminate water so, if you supply water, clean the bowl frequently to avoid picking up salmonella and other nasty bacteria on your hands. Wash the container and your hands well away from any food preparation or bathroom areas. Throw away seed stored in trashcans from the previous season. Tainted seed can cause illness in your backyard diners. Fresh birdseed is less likely to mold.

Do birdfeeders help or hurt wildlife? Studies show they are merely supplemental food sources. Cornell University has done extensive research in the area, including a 30-year study of backyard birds that has taken advantage of all those bird feeders out there.

Through feeding backyard birds, you bring nature up close to observe the fascinating nuances of our indigenous bird life. You may discover how to differentiate a male from a female woodpecker by noting the amount of red on the head. You might delight in seeing the gradual change of the drab olive goldfinches during non-breeding times to the spectacular bright yellow breeding colors of approaching spring. You may even glimpse a male cardinal’s courtship of feeding his ladylove a seed right at your back window. While you enjoy the natural history lesson, the birds are benefiting from a boost in their diet. With proper care, backyard bird feeding can be a win-win situation, and that is something to crow about.

Author and Naturalist Suzanne Holland is the Visitor Services Manager at Hidden Oaks Nature Center in Annandale, Va.

The Link Between Beavers and Water Quality

Beaver 1When you hear of a new development, usually you think of a new business, house or apartment complex. It might surprise you, if you live next to a park, to learn that new houses are rising all the time near you. They’re houses for wildlife, and they’re often built by beavers.

Beaver 2Beavers don’t know the difference between a nice, ornamental crape myrtle in your yard and a Virginia pine standing on parkland. That’s sometimes a source of disagreement as to the true value of beaver houses. However, a three-year study by U.S. Geological Survey (USGS) Ecologist Dan Kroes shows their value in streams.

The USGS study shows that dams and lodges, as beaver houses are properly called, are important to water quality. Dams trap as much as two feet of sediment that would otherwise go downstream. Sediment in water is what makes streams cloudy or murky. Not only are sediment-filled streams unpleasant to look at, they don’t allow sunlight to play its role in aquatic food webs. If there are lakes downstream, the sediment settles and may eventually fill those lakes. Witness Lake Accotink in Springfield. It was 23 feet deep  when it was constructed in the 1940s, and despite numerous dredging efforts, it was a mere four feet deep by 2018.

Beaver dams and lodges also slow the water tumbling downstream. By extension, they reduce stream bank erosion that undercuts banks and fells trees. They slow the pace of streams, which improves drinking water quality, increases stream life and decreases flooding. It’s development that’s good for the environment.


No Child Left Inside at Hidden Oaks’ Nature Playce

Nature Place_0245Whatever happened to parents saying, “Go outside and play?”

In nature, it’s just as important to know what not to be afraid of as it is to know what to fear. Unfortunately, in our increasingly urban county, some parents have become so fearful of what might be out there that they won’t even let their kids play in the back yard.

That’s where Nature Playce at Hidden Oaks Nature Center comes in. Hidden Oaks Visitor Services Manager Suzanne Holland says the play area is designed for nature-phobic parents as well as for their three- to ten-year-old children.

In speaking with parents, Holland found that many limit their children’s time in nature because they’re worried about everything from insect stings and bird flu to poison ivy and poison oak. Nature Playce addresses those fears through education and a woodland area cleared of many things a parent may find threatening. Since 2008, Hidden Oaks staff has encouraged preschool teachers and other child care professionals to embrace taking children outside for traditionally indoor activities and include unstructured play in their curriculum. There are monthly three-hour workshops for the Institute of Early Learning, a division of Fairfax County Office for Children, that focus on Nature Playce and how to use outdoor play to engage children in both cultural history and nature.Nature Place 3

Off the Beaten Path

Part of Nature Playce’s appeal to children is letting them break some rules. For example, there is no trail to stay on. Children can roam the one-third acre area, pick up stones and roll logs to see what’s underneath. They can hop across stumps known as tree cookies and walk on a log. Touching is a “yes” activity. Kids can even make mud pies.

Before entering Nature Playce, parents are encouraged to visit the nature center for a ten-minute introduction to playing safely outdoors. Children and adults get tips on such things as how to identify a copperhead snake and avoid poison ivy, how to safely handle a worm, and how to figure out which bugs are safe to touch. They also learn how to roll a log and why the log should be replaced.

After the introduction, children are dubbed official “Nature Snoopers” and receive “a key” to the play area – a large, colorful magnifying glass. They are invited to explore with a Nature Snooper’s pail of goodies – digging tools, cups, books and feathers.

Nature Place 4Naturalists keep the play area as safe for young children as possible by clearing out such things as poison ivy. A low, split rail fence surrounding the area provides a sense of security. Once children pass through the gate, they can venture through four areas that present new opportunities for fun and that grow progressively “wilder.” They’ll discover a waterscape surrounded by boulders to climb, supports to make a fort, a dirt pit for digging, hidden dinosaur tracks, fallen trees to balance upon, and stumps and rocks to overturn. Parents can sit back on rustic benches and watch the kids explore or join in the fun.

Nature Place 1Holland says the area is designed to “provide assurances for parents while stimulating a sense of wonder.” Children need an adult to support their exploration, and she says her hope is that “as parents and children become more open to having an adventure, they’ll be more willing to go into their back yards.” Parents can join an email list to learn about other activities and programs at the center.

The typical response from parents who visit Nature Playce? Holland says she often hears, “What a great idea. I used to love to play outside,” or “My friend needs to bring her kids out here with us. She is not as comfortable with bugs as we are.”

Nature Playce Targets Nature Deficit Disorder

Is there such a thing as being too safe with our kids? If it means disconnecting them from nature, the answer is yes. That’s Richard Louv’s argument in his book Last Child in the Woods, the inspiration for Nature Playce at Hidden Oaks Nature Center.

Today’s parents are familiar with Attention Deficit Disorder and No Child Left Behind laws. Nature Playce exists to combat the growing Nature Deficit Disorder among today’s children and support the No Child Left Inside movement.

The Children and Nature Network says researchers have found connecting with nature can:

  • Increase creativity and school achievement
  • Increase focus
  • Reduce stress
  • Increase cooperation
  • Reduce aggression

Nature Place 5Holland says unmasking the outdoors for children fosters an appreciation for nature and environmentalism. By getting kids outside, you plant seeds for the “environmental stewards of the future who will care enough to vote to protect trees, wildlife and other green issues.”

Hidden Oaks will celebrate the 10th anniversary of Nature Playce on September 29, 2018. There will be an open house during an afternoon of activities in Nature Playce and at the nature center.

Nature Playce is on the web at

Author Carol Ochs works in the Park Authority’s Public Information Office.

Are There Deer Resistant Plants?

1If they’re hungry enough, deer will eat anything.

Fairfax County has hungry deer. Understanding that deer will eat most plants is one of the first and most important rules to learn about gardening in Fairfax County. There are many lists swearing that deer will avoid certain species, but we’ve planted them, and deer have eaten them.

2A physical barrier, like an eight-to-ten-foot fence, can be effective at thwarting deer. Note that if deer know about the garden before the fence goes up, they’ll try to get in again. Another possibility is a shorter, double fence, perhaps four feet high. That may confuse deer enough to keep them out.

Not all homeowners’ associations in Fairfax allow fences, and not all budgets can hold one, so that brings us to the question of 3which plants to use. You can find some choices in the library at Green Spring Gardens. Following are some we like for their garden attributes and because they are native species.


The trick with trees is to get them tall enough to avoid damage from grazing. Tree protectors can help. They’re miniature fences that fit around individual trees.

Common Names: beech, birch, black locust, maples and oaks

Scientific Names: Fagus grandifolia (Beech), Betula Nigra (River Birch), Robinia pseudoacacia (Black Locust), Acer rubrum (Red Maple – beware, many cultivars are hybrids with non-native maples), Acer saccharinum (Silver Maple), Quercus alba (White Oak), Quercus phellos (Willow Oak).


Common Names: American Bayberry, Beautyberry, Sweet-bay Magnolia, Red Buckeye, Summersweet, and some viburnums (make sure they are a native, like Arrowood or Maple-leaf)

Scientific Names: Myrica cerifera (American bayberry), Callicarpa americana (Beautyberry), Magnolia virginiana var. australis (Sweet-bay Magnolia), Aesculus parvia (Red buckeye), Clethra alnifolia (Summersweet), and some viburnums (make sure they are a native, like Viburnum dentatum (Arrowood) or Viburnum acerfolium (Maple-leaf)).


Common Names: Anenome, Astilbe, Beardtounge, Bee balm, Big-root Geranium, Blazing Star, Blue Star, Celandine Poppy, Columbine, Orange Coneflower, False Indigo, Ferns, Foamflower, Goldenrod, Ironweed, Jack-in-the-pulpit, Joe-pye Weed, Lobelia, Obedient Plant, Partridgeberry, Phlox, Shooting Star, Skullcap, Tickseed, Trout Lily, Wild Ginger

Scientific Names: Thalictrum thalictroides (Rue Anemone), Astilbe biternata (Astilbe), Penstemon angustifolius (Beardtounge), Monarda didyma (Bee Balm), Geranium macrorrhizum (Big-root Geranium), Liatris spicata (Blazing Star), Amsonia ciliate (Blue Star), Stylophorum disphyllym (Celandine Poppy), Aquilegia canadensis (Columbine), Rudbeckia fulgida (Orange Coneflower), Baptisia australis (False Indigo), Pteridium aquilinum (Bracken Fern), Osmunda cinnamomea (Cinnamon Fern), Tiarella cordifolia (Foamflower), Solidago ssp. (Goldenrod), Vernonia noveboracensis (Ironweed), Arisaema triphyllum (Jack-in-the-pulpit), Eupatorium purpureum (Joe Pye Weed), Lobelia cardinalis (Lobelia), Physostegia virginiana (Obedient Plant), Mitchella repens (Partridgeberry), Phlox paniculata (Phlox), Dodecatheon meadia (Shooting Star), Scutellaria ovata ssp. virginiana (Skullcap), Coreopsis lanceolata (Tickseed), Erythronium americanum (Trout Lily), Asarum canadense (Wild Ginger)