Bring in the Rare Butterflies

Like many of us, I enjoy browsing local nurseries. Often, you can run across a plant, shrub, or tree that you don’t see too often—something less likely to happen at gardening departments in big box stores. For example, about a year ago while browsing I noticed a tree for sale not often found in the garden trade in the Northeast: the Common Hackberry (Celtis occidentalis). I snatched it up immediately and planted it in a sunny place in my back yard. In the wild, this tree is grows in the alkaline soils of forests, near streams and rivers, and regenerating fields. But in your yard or garden it is very accommodating in a variety of soils in part-sun to sunny conditions.

Most herbaceous plants, shrubs, and trees take a few years to adjust to their new site, going through what’s generally called “sleep, creep, leap.” That is, they are relatively dormant the first year, start active growth the second, and flower in the third. My hackberry is thriving in its second year and putting on lots of new growth.

Why did I jump at the chance to plant a hackberry? The answer is simple: butterflies! Attracting a variety of birds to your yard with this tree is a plus, but it is the possibility of bringing in some rare butterflies that is the real bonus. There are a few butterfly species whose larvae (caterpillars) feed only on this tree. They include the Hackberry Emperor (Asterocampa celtis), the Tawny Emperor (Asterocampa clyton), and the American Snout (Libytheana carinenta). Although none are common, of these three species the Hackberry Emperor is the most often seen. The American Snout is seen only occasionally because it does not overwinter here, but migrates from the south.

Hackberry trees are members of the elm family (Cannabaceae). In the Midwest this tree is often used as a substitute street tree for the American Elm (Ulmus americana), which has been eliminated in many areas by Dutch elm disease.

The leaves of both American Elm and Common Hackberry are toothed. Elm leaves have a more oval shape and hackberry leaves are more elongated and pointed at the tip. Another way to identify a Common Hackberry tree is by its distinctive bark. The light to dark gray bark has pebbly, warty outgrowths on young trees that develop into corky, projecting long ridges on older trees.

The common name hackberry is from the Old Icelandic heggr meaning “bird-cherry tree” and ber meaning “berry.” Early colonists confused the hackberry’s fruits with the round, fleshy fruits of the Bird Cherry or Hagberry (Prunus padus), a common Old World tree in the Northern Hemisphere. Both trees attract many types of birds to their fruit.

Hackberry produces an abundant crop of orange-red to dark purple drupes, which are one-seeded fruits. Fleshy parts of the fruit are edible and taste a bit sweet, hence another of its names is Sugarberry. However, there is a related species also called Sugarberry (Celtis laevigata) found in the southeastern United States.

Let’s get back to those rare butterflies. As adults, the Hackberry Emperor and the Tawny Emperor feed on tree sap, carrion, rotting fruit, and animal dung. The American Snout nectars on a variety of plants, including dogbanes (Apocynum spp.), Sweet Pepperbush (Clethra alnifolia), and goldenrods (Solidago spp. and Euthamia spp.).

The two Emperors are often associated with each other. Researchers have found that they display niche partitioning. That is, they don’t compete with each other. Tawny Emperor larvae usually feed on older leaves, whereas Hackberry Emperor larvae feed on younger leaves.

So keep an eye out for this remarkable tree. If you find it and have room in your yard, plant one. Before you know it, you’ll be hosting and enjoying some rare native butterflies.