Observing a non-native butterfly bush (Buddleia davidii) swarming with bees and butterflies, a gardener might easily be convinced that all nectar and pollen-producing plants are equally beneficial. While many of our native pollinators can make use of nectar and pollen from exotic plants, the full picture is a bit more complicated for native plants.
The native butterflies, bees, beetles, and beneficial wasps that fill our gardens with color and movement represent just one stage of these insects’ development: adulthood. These adults drink nectar and gather pollen, simultaneously providing the important service of pollinating flowers so they produce fruit and seeds. But before winging into your garden, these insects were various types of larvae.
During this stage of development, most species are totally dependent on host plants – food sources with which they co-evolved. Though we primarily associate pollinators with flowers, many of them rely on foliage for food during this early stage. Our native oak trees (Quercus spp.) are hosts to more than 400 species of butterflies and moths. Woody plants in the Prunus genus, including wild cherry (Prunus serotina) feed more than 300 species of caterpillars.
Recent campaigns to save the monarch butterfly from extinction have increased awareness of that species’ reliance on milkweeds (Asclepias spp.); however, this is only one of many such interdependent relationships. Orange butterfly weed (Asclepias tuberosa) serves as a host for queen butterflies and tiger moths, as well as monarchs, and provides nectar for a host of insects.
Rattlesnake master (Eryngium yuccifolium), another native perennial noted for the diversity of insects it attracts, is a host plant for black swallowtail butterflies and a threatened moth species. Some pollinators remain picky about their food sources even as adults. There are 14 types of native bees that rely solely on blueberries (Vaccinium spp.) to feed themselves and their young.
Pollinators are not the only reason to add host plants to your garden. Abundant caterpillars are also critical for the survival of birds. Entomologist Doug Tallamy says that 96 percent of our native bird species rely on caterpillars to feed their young. Based on research done by Tallamy and others at the University of Delaware, the National Wildlife Federation has created a database of Keystone Native Plants for each of the eight ecoregions that comprise North America.
Keystone Natives either host a diversity of larvae or provide food for specialist bees. Topping the list of flowering perennials for our region are goldenrods (Solidago spp.) and asters (Symphyotrichum spp.), which like rattlesnake master, do double duty as both host plants for hundreds of caterpillars and nectar sources for scores of specialist bees.
The loss of two trees in my front yard has created a new sunny spot where I hope to attract more pollinators. The space will accommodate a large grouping of rattlesnake master and dotted horsemint (Monarda punctata). Research indicates that larger clumps of a single species attract more pollinators than single plants scattered across a wider area. My new area is close to a sunny border containing milkweed and downy skullcap (Scutellaria incana), a bumblebee favorite. Other pollinator-friendly plants, including New Jersey tea (Ceanothus americanus), are nearby.
The Xerces Society suggests adding more native plants to your landscape as the first of four steps to attract and support native pollinators. While gardeners may enjoy having something in bloom throughout the growing season, pollinators absolutely depend on our flowers each day for food. To make achieving that goal less daunting, the Society’s website includes lists of perennials, shrubs, and trees, by region. Gardeners can use the list to identify host plants and establish a continuum of nectar – and pollen-producing flowers.
The second recommended step is to consider native pollinators’ needs during all phases of their life cycles. Pollinator gardens should provide resting and nesting spots as well as nectar and host plants. Many native bees and butterflies spend part of their lives in accumulated leaf litter or require nest sites in bare patches of ground. Others overwinter in plant stems, so we shouldn’t rush to cut back and tidy our gardens before spring.
Perhaps the single most important step gardeners can take to support pollinators is to avoid the use of pesticides and other chemicals. Insecticides sprayed on foliage may not impact pollinators visiting flowers, but they do kill feeding larvae and adults who use foliage as resting places.
Finally, the Xerces Society asks gardeners to spread the word about the important role home landscapes can play in supporting pollinator habitat and diversity.
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Dale Batchelor owns Gardener by Nature LLC, a residential design and consultation company in Raleigh emphasizing sustainable landscapes and native plants. With her husband, John Thomas, she co-created Swiftbrook Gardens, a habitat certified by the N.C. Native Plant Society and the National Wildlife Federation.