Butterflies and flowers could be considered a match made in heaven. Flowers provide butterflies with sugary nectars for food. Butterflies in turn transfer pollen from one flower to another — a process called pollination — which guarantees fruit and seed production. This interaction is a poignant example of Earth’s “tapestry of life.”
However, while it is true that butterflies prefer specific plants for feeding, especially flowering annuals and perennials, they most often select other varieties of plants for reproduction. Remember that butterflies have a metamorphic life cycle consisting of four stages: egg, larva (caterpillar), pupa (chrysalis), and adult (butterfly). The plants that trigger egg-laying by female butterflies are called hosts or host plants. While the majority of these are also flowering annuals or perennials, surprisingly many are actually trees and tall shrubs.
Take my home state of Louisiana, for example. As an entomologist I have documented proof that of the state’s 125 resident butterfly species, at least 40 lay their eggs on trees and tall shrubs. That’s 32 percent. Oaks rank the highest, being utilized by 12 butterfly species. Of course, geography plays a role, so both butterfly species and host trees vary from region to region. Regardless of locality, however, certain trees habitually rank as important butterfly hosts, and these should be embraced by butterfly stewards.
About plant hosts
By their very nature, trees grow tall and produce shade, which is great for homeowners, but disastrous for the garden’s sun-loving, butterfly-friendly plants. There are reasonable solutions, though.
For urban homeowners, host trees can be positioned a slight distance from the actual garden, which will eliminate shade within the garden. Another alternative is to plant trees and shrubs along property lines.
For those who own sizable acreage, such as farm ground or grazing lands, there is an even greater solution: hedgerows or fencerows. These are defined as narrow belts of heavy vegetation that flank fences erected to delineate property boundaries or separate sections of open lands. Historically and around the world, large landowners, farmers, biologists, conservationists and hunters, to name a few, have had a healthy respect for these overgrown swaths of trees and bushes. Dense greenery acts as a windbreak and creates shade for both livestock and humans. It also provides important habitat, such as cover, space for raising young, and food — think foliage, berries, fruits, nuts and more — for local birds, rabbits, squirrels, foxes, deer, turkeys, and myriad small amphibians, reptiles and insects. In addition, the dense greenery constitutes good venues for time-honored sport hunting. (Recall those high-spirited and colorfully costumed foxhound hunts featured in so many classic British movies.)
Change in the ‘90s
Times have changed, though, and it’s important to consider genetically modified organisms (GMOs) now. First marketed in the United States in 1994, GMOs have become increasingly popular with farmers and agro-chemical manufacturers. Of particular concern to butterflies and other pollinators are those crops that have been engineered to be resistant to common chemicals in the form of herbicides used to control weeds in agriculture fields. In the agriculture community, the term “weed” is generally used for any unwanted plant species, including native wildflowers. The new seed crops are labeled “Glyphosate-resistant” and “Roundup Ready.” In the U.S., transgenic crops currently include corn, soybean, cotton, canola-rapeseed, sugar beet, alfalfa, papaya and squash, with more on the way.
It used to be that fields were sprayed either by air or ground to kill volunteer weeds in early spring, just prior to the sowing of crop seeds. Any weeds that later sprouted between rows were tolerated, or if too dense, target sprayed by hand, which was a laborious undertaking. Today, however, with herbicide-resistant crops, farmers can broadcast spray when weeds are most problematic — meaning that they are flowering and producing seeds. GMO crops, therefore, are advertised to make farms tidier, to save farmers labor and money, and to reduce the volume and types of chemicals needed for high crop yield.
While this may seem like a blessing, the practice is not without controversy. The major challenge is that broadcast spraying throughout the growing season is too efficient, meaning that the herbicides kill all non-crop species, including those nectar- and pollen-producing wildflowers that constitute important food sources for pollinators like butterflies, honeybees and bumblebees. From an ecological perspective, biological diversity plummets. Some species are even now threatened with extinction, and many crops, such as fruit trees, are on a rapid decline. None of this is good.
Case in point
The monarch butterfly (Danaus plexippus), icon of American butterflies and animal migrations, is quite picky when it comes to reproducing: Females lay their eggs exclusively on milkweed plants (Asclepias spp.) — those 140-plus species of low-growing, sun-loving perennials that produce milky sap, showy flowers and silky seeds, and that are notorious for invading disturbed soils. Understandably, farmers regard milkweed plants as major pests to be eliminated, and GMOs do a great job at this.
Recently, however, butterfly professionals and enthusiasts have noted a seemingly simultaneous reduction in monarch butterflies. In fact, researchers who study monarchs in their mass overwintering grounds in central Mexico have documented that during the winter of 2013-2014, the monarch population was the lowest since 1994-1995, when record-keeping first began. According to environmentalists and conservationists, the low numbers of both milkweeds and monarchs are telltale, not coincidental. One theory proposes that monarch decline can be tied directly to the butterfly’s loss of breeding habitat, particularly throughout the American heartland.
With a little tweaking, perhaps traditional fence-rows can offer hope. Certainly, fencerows should be maintained, if not widened. Furthermore, because weed control usually bypasses border vegetation, the sunny margins of these noncultivated lands can be recruited for the reintroduction of native wildflowers. Custodians of rural lands could help matters by clearing a 5- to 10-foot swath of land adjacent to their pre-existing fencerows.
Clearing can be accomplished by burning, tractor mowing, or goat browsing (see “Raising Goats for Land Clearing” by Ed Wynn). This new shoulder should be sowed in late winter or early spring with seeds of native wildflowers, including local milkweeds. Seeds can be collected from the wild or purchased from commercial distributors offering regional species. The wildflowers offer a sunny banquet for local pollinators and associated wildlife as compensation for losses brought on by farming with high-tech transgenic crops. Each year, the wildflowers should reseed on their own with minimal maintenance, such as an occasional burning, mowing or browsing by goats. It should be noted that although milkweeds can be toxic to livestock, the plants have a strong bitter taste, which strongly discourages grazing by animals.
This 21st-century makeover to a historic wildlife-friendly landscape creates new possibilities for conserving currently endangered pollinators like butterflies and bees. And while you’re at it, add to your personal garden a showy species of milkweed — butterfly weed (Asclepias tuberosa) and common milkweed (A. syriaca) are attractive and serve as hosts for monarchs as well as general nectar plants for pollinators throughout the greater U.S. There’s no need to worry about the monarch caterpillars attacking your prize plants, because monarch larvae feed only on milkweeds.
This simple act will brighten your garden, provide monarchs with a place to begin a new generation, and feed many local pollinators.
And for you personally? Imagine the satisfaction you’ll get knowing that you are part of the solution to a serious new environmental threat. Now, that’s some true grit!
Read more: Visit the Butterfly House at the Missouri Botanical Garden in St. Louis.
Butterflies and Host Trees
Two of the most common trees that thrive in border vegetation, particularly east of the Rockies, are Osage orange (also called bois d’arc, hedge, hedge apple, and horse apple) and, in the southeast, Chinese tallow tree (a non-native species that has become naturalized). Neither are butterfly hosts, regrettably. However, many other fencerow-friendly trees and tall shrubs are indeed well-known hosts for many native butterflies.
Consider the following:
Common butterflies using one or more of these species include:
• American Snout
• Mourning Cloak
• Painted Lady
• Question Mark
• Spring Azure
• Silver-Spotted Skipper
• Admirals, Commas, Emperors, Sisters, Swallowtails (most)
• Elfins and Hairstreaks (many)
Gary Noel Ross, Ph.D., is a retired professor of entomology residing in Baton Rouge, Louisiana. He is a John Burroughs award-winning nature writer, is affiliated with the McGuire Center for Lepidoptera and Biodiversity at the University of Florida, and is the director of butterfly festivals for the North American Butterfly Association.