Butterflybush – Are there better alternatives?

About a year ago I was asked by the editor of Butterfly Gardener, a publication of the North American Butterfly Association, to take the ‘con’ side in a debate about whether to use Butterflybush.  I knew it was invasive, but until I started to research the article, I didn’t realize the extent of its reach.

It’s all about the next generation: The Caterpillars

There’s no denying that Butterflybush (Buddleja davidii), also called Orange Eye Butterflybush, can be a lovely plant. In a sunny location it has attractive flowers, blooms for a long period of time, and may draw a variety of species of adult butterflies for nectaring. What more could a butterfly gardener want? What else is there to know?

What about caterpillars?

Pipevine Swallowtail Caterpillar on Dutchman's Pipevine (Aristolochia macrophylla)

Pipevine Swallowtail Caterpillar on Dutchman’s Pipevine (Aristolochia macrophylla)

In Butterflies Through Binoculars, Jeffrey Glassberg says “The most important factor contributing to the decline of butterfly species is habitat loss.” Glassberg also states “For many uncommon butterflies the easiest way to locate colonies is to search for sites where the foodplant is common.” By food plant, he means the plant(s) on which the next generation, the caterpillars, can feed and thrive. Perpetuation of butterfly species requires habitat that will support a butterfly’s full life cycle, not just the adult stage.

Kenn Kaufman, in his Field Guide to Butterflies of North America, states “A butterfly’s most important relationship is with the plants eaten by its caterpillars”. Butterflies of the East Coast: An Observer’s Guide by Rick Cech and Guy Tudor notes “the most important single determinant of butterfly distributions, as well as many other aspects of their lives” are the butterfly’s “host plants”, the food plants that caterpillars need to survive.

None of these sources identify Butterflybush as a food plant for butterfly caterpillars. Does it provide food for the hungry caterpillars of any species of butterflies or moths native to North America? A search of the Natural History Museum’s database of known host plants yields only one species of Lepidoptera present in North America as using Butterflybush as a food plant, the Buddelja Budworm Moth, present only in urban areas of California and thought to be introduced there. So it’s not a known caterpillar food plant. Even if a caterpillar is spotted on Butterflybush, more study would be necessary to see if it gets sufficient nutrition to successfully become an adult.

Isn’t it enough that Butterflybush is a good nectar source?

It would be, except for one thing.

The Orange Eye Butterflybush Plant Fact Sheet from the USDA Natural Resources Conservation Service includes a bright red warning, “Caution: This plant may become invasive.” The USDA lists it as naturalized in 20 states, British Columbia, and Puerto Rico. This means it has escaped from gardens to surrounding natural areas, with the potential to crowd out native vegetation that is essential to wildlife, including butterflies and birds. And is difficult to remove once it has established itself.

According to the USDA, Butterflybush (except for a few sterile cultivars) is prohibited for entry, transport, purchase, sale or propagation in the state of Oregon. It is prohibited from being propagated, released, displayed or sold in New Zealand, is listed as one of the top 20 weeds in Western Europe, and in 2007, the US Fish and Wildlife Service Bayscapes program listed it as a plant that should no longer be used for landscaping. (Soure: The Invasive Buddleja davidii (butterfly bush).(Report), The Botanical Review, September 1, 2009, Tallent-Halsell, Nita G.; Watt, Michael S.)

It’s not that Butterflybush is inherently a bad plant. It is native to China, not North America, Europe or New Zealand. The insects, birds and other residents with which it evolved in China and that depend on it for food there aren’t present in the areas in which it was introduced. So there are no species here that will naturally keep it in check. This is always a potential danger when a species is introduced in an environment in which it is not native, where its food web partners are missing.

A sterile cultivar might be worth a try, but they have a tendency to evolve back into a fertile state over time, so they may become a problem further down the road. Is it worth the risk? (See Developing Sterile Invasives by Ellen Susa )

There are better alternatives

The good news is that there are lots of great alternatives to Butterflybush.

For caterpillar food plants, consider trees and shrubs like Black Cherry (Prunus serotina), Tuliptree (Liriodendron tulipifera), Oaks, Northern Spicebush (Lindera benzoin), blueberries (Vaccinium corymbosum, V. augustifolium), Gray Dogwood (Cornus racemosa), Ninebark (Physocarpus opulifolius), Hoptree (Ptelea trifoliata) and Pipevine (Aristolochia species), and herbaceous perennials including American or Maryland Senna (Senna hebecarpa, S. marilandica), Blue False Indigo (Baptisia australis), violets, milkweeds and asters.

Azure laying eggs (ovipositing) on  Ninebark (Physocarpus opulifolius)

Azure laying eggs (ovipositing) on Ninebark (Physocarpus opulifolius)

Red Admiral Nectaring on Ninebark

Red Admiral Nectaring on Ninebark

For nectar, in addition to the plants listed above, you can’t beat Mountain Mints, Common Buttonbush (Cephalanthus occidentalis),

Indian Skipper and Bumble Bee nectaring on Buttonbush (Cephalanthus occidentalis)

Indian Skipper and Bumble Bee nectaring on Buttonbush (Cephalanthus occidentalis)

and Coastal Sweetpepperbush (Clethra alnifolia). What thirsty butterfly could resist pink clouds of Joe-Pye-Weed (Eutrochium species),

Eastern Tiger Swallowtails and Peck's Skippers nectaring on Joe-pye-weed (Eupatoriadelphus species)

Eastern Tiger Swallowtails and Peck’s Skippers nectaring on Joe-pye-weed (Eupatoriadelphus species)

bold purple New York Ironweed (Vernonia noveboracensis),

Zabulon Skipper nectaring on New York Ironweed (Vernonia noveboracensis)

Zabulon Skipper nectaring on New York Ironweed (Vernonia noveboracensis)

Northern Blazing Star (Liatris scariosa),

Monarch on Northern Blazing Star (Liatris scariosa)

Monarch on Northern Blazing Star (Liatris scariosa)

Purple Giant Hyssop (Agastache scrofulariifolia), or sunburst yellow coneflowers?

Green-headed Coneflower (Rudbeckia laciniata) with American Copper and Bumble Bee

Green-headed Coneflower (Rudbeckia laciniata) with American Copper and Bumble Bee

From late summer through fall, the shimmering yellows of goldenrods

Common Buckeye and Potter Wasp on Goldenrod

Common Buckeye and Potter Wasp on Goldenrod

and the many bright hues of asters are a prolific source of food for hungry butterflies and native bee species, while hosting many other insects that provide essential food for birds.

Orange Sulphur nectaring on Aster

Orange Sulphur nectaring on Aster

Listed above and pictured here are just a few of my personal favorites. Good sources of information about plants that will work well in your area include Attracting Native Pollinators by Mader, Shephard, Vaughan, Black and LeBuhn; Bringing Nature Home by Douglas W. Tallamy, the North American Butterfly Association website, and your state or regional native plant society.

Most of us (except in places where prohibited, like Oregon and New Zealand!) are free to choose. Would you like to have a chance to watch butterfly species successfully raise new generations on your property, and protect their habitat in the natural areas near you? Choose well, and you will also have a continuously changing display of colorful blossoms to host adult butterflies from early spring through late fall.

Note: This is adapted from an article that appeared in the Summer 2012 issue of Butterfly Gardener, a publication of the North American Butterfly Association.

Pipevine Swallowtail Butterflies and Their Host, Dutchman’s Pipevine

Late one afternoon a pair of dazzling creatures caught my eye as I walked toward my car in the parking lot at Bowman’s Hill Wildflower Preserve.  They were Pipevine Swallowtail butterflies, a male and a female, flitting about in the neighborhood of a very large Dutchman’s Pipevine (Aristolochia macrophylla), the plant that gives them their name.

As I watched, the female occasionally landed on the Dutchman’s Pipevine, staying in one spot for a few moments, with her lower abdomen curved slightly to touch the Pipevine leaves or stems.  She was laying eggs!  In the photo below, two roundish orange eggs are visible on the stem of the vine, next to her right front leg.  If you look carefully at the tip of her abdomen, you can see a spot of orange – she’s just about to lay another.

Pipevine Swallowtail Butterfly laying eggs on Dutchman’s Pipevine

Some butterflies have evolved a survival strategy that enables their caterpillars to feed on a wide variety of plants, but others, like the Pipevine Swallowtail, have chosen to specialize on a small number of plants that give them a particular advantage.  To protect itself from being eaten, Dutchman’s Pipevine has evolved with chemicals that are at minimum distasteful to those who would eat it, and if a sufficient amount is ingested, they are toxic.  Pipevine Swallowtail caterpillars are among the few creatures who are able to process these chemicals without harm to themselves, then store them in their bodies in such a way that they are toxic to their potential predators.  This chemical protection even survives metamorphosis and extends to the adult butterfly.  It is so effective that other butterflies mimic the appearance of the Pipevine Swallowtail, since this is often enough to warn off predators.

Pipevine Swallowtails lay their eggs in small clusters of usually less than twenty, often on young leaves or stems of Pipevine plants, members of the genus Aristolochia.  In the mid-Atlantic, the only species that Pipevine Swallowtail caterpillars can eat are Dutchman’s Pipevine and Virginia Snakeroot.  In the southwestern part of its range, there are other native Pipevine species that this butterfly uses as its caterpillar food plants.

Pipevine Swallowtail Eggs on Dutchman’s Pipevine

Soon after they hatch, the young caterpillars have a reddish spiny appearance. They tend to feed together in groups.

Young Pipevine Swallowtail Caterpillars

Older caterpillars usually feed alone, and their appearance changes, with colors appropriate for Halloween – black with orange trim.

Pipevine Swallowtail Caterpillar on Dutchman’s Pipevine

Adult butterflies feed on a variety of plants for their nectar, and may also seek out minerals at puddles.  They don’t feed on the flowers of the Pipevines, however, because they are not a good anatomical match for feeding or pollination.

Dutchman’s Pipevine is a deciduous vine with large heart-shaped leaves, but it is named for the shape of its flowers, which have a curved tubular shape ending in a flair with an opening in the center to allow pollinators to enter and search for a nectar reward.  The graceful Pipevine Swallowtail is too large to enter, and even its proboscis can’t extend enough to navigate the long curved tube to reach the flower’s food offerings.

Dutchman’s Pipevine Flower in bloom

So how are the Pipevine flowers pollinated?  Small flies and gnats are attracted to the open throat of the flower by an aroma they can detect, and by the color pattern, both directing them forward down the tube.  As the insects enter, they are prevented from reversing course by hairs that line the flower’s throat, forcing the insect forward, a little like the metal spikes at parking lot entrances that will puncture your tires if you back up.  When the insect reaches the nectar source, it meets the sticky stigma of the female flower parts, depositing pollen brought in on its body from another Pipevine flower.  The plant detains the insect until the flower has been fertilized, offering it shelter and nectar, sort of like a little insect bed and breakfast.  The female flower parts wither, and the male parts mature, releasing pollen for the insect to pick up on its body.  The flower tube and its hairs relax enough for the insect to escape the way it entered, taking the pollen to the next flower it visits, ensuring the continuation of both the Dutchman’s Pipevine and the Pipevine Swallowtail species.

Dutchmans Pipevine on fence at Bowman’s Hill Wildflower Preserve