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?
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.
For nectar, in addition to the plants listed above, you can’t beat Mountain Mints, Common Buttonbush (Cephalanthus occidentalis),
and Coastal Sweetpepperbush (Clethra alnifolia). What thirsty butterfly could resist pink clouds of Joe-Pye-Weed (Eutrochium species),
bold purple New York Ironweed (Vernonia noveboracensis),
Northern Blazing Star (Liatris scariosa),
Purple Giant Hyssop (Agastache scrofulariifolia), or sunburst yellow coneflowers?
From late summer through fall, the shimmering yellows of goldenrods
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.
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.