Diggin’ In: Dogbane: Good for insects, bad for dogs

October 10, 2016

Interesting fruits and seeds in the fall garden add a visual interest that draws the eye as much as stunning flowers do.

Summer-flowering native dogbane is one of those very plants.

"After pollination, fruits appear as long cylinders that split open, releasing seeds covered with long tufts of silky hairs, easily dispersed by the wind," says Helen Hamilton, past president of the John Clayton Chapter, Virginia Native Plant Society, and retired biology teacher living in Williamsburg, Va.

Dogbane, or Apocynum cannabinum, is a shrub-like herbaceous perennial that grows 3 to 5 feet tall with attractive purplish stems that branch near the top, according to Hamilton. Like milkweeds, which they superficially resemble, both stems and leaves produce a milky sap when broken. Monarchs and other butterflies sip nectar from the flowers and occasionally lay a few eggs, but none develop into caterpillars.

May through July, white bell-like flowers, sweetly fragrant, appear in clusters at the ends of branches. The flowers produce lots of nectar and attract many kinds of insects — bees, beetles, bugs and butterflies.

Easy to grow with erect stems, dogbane fits nicely at the back of a perennial border or at the edge of woodlands, but the plant spreads quickly from underground rhizomes and can be too aggressive for a small garden, advises Hamilton. Dogbane prefers full sun and somewhat moist soils but tolerates both flooding and drought. The plant grows naturally in all counties of Virginia and throughout the United States and Canada.

The common name, dogbane, refers to the plant’s toxic nature, which has been described as "poisonous to dogs," but it is poisonous to animals and humans alike. Apocynum means "away, dog" and cannabinum means "like hemp," in reference to the strong cordage that was made by weaving together the stem’s long fibers.

Also known as "Indian hemp," Native American women made miles and miles of twine from the long fibers in the stems of dogbane. Their homes were constructed of vertical and horizontal poles covered with bent saplings, all lashed together with dogbane twine, which also furnished fishnets, baskets, mats and ropes.

"Such uses are thousands of years old — remnants of dogbane fibers have been found in ancient archeological sites," Hamilton says.

Attracting pearl crescent butterflies

If you see a medium-sized orange and black butterfly without the tails of a swallowtail butterfly, you can bet it’s a pearl crescent, or Phyciodes tharos.

Adrienne Frank, coordinator of the Butterfly Circles in the Williamsburg area, says: "Pearl crescents are named for the tiny moon-crescent shape on its hindwing, seen when the wings are folded up (closed). They are sometimes known as ‘pearly crescentspot.’"

In Hampton Roads, there are several broods each year, which is why pearl crescents are seen nearly all season, feeding on many flower species, according to Hamilton. Their favorites include dogbane, asters, swamp milkweed, black-eyed susans and thistles, all plants that thrive in full sun and open areas.

"This year was a good year for them in our area," Frank says.

"We’ve had them in our home garden almost all summer long. We’ve seen them on a wide array of flowering plants, probably because they have small mouth parts. They seemed particularly interested in yellow cone flowers and mountain mint."

Male pearl crescents are distinguished by black knobs on their antennae, according to Hamilton. The female lays her eggs in small groups on the underside of aster leaves, their host plants. Several species of asters are familiar food for the growing larvae, including Frost Aster (Symphyotrichum pilosum) and Smooth Aster (Symphyotrichum laeve), fall-blooming plants with multiple flowers on branching stems. The larvae are dark brown with a light line and covered with black bristly spines.

Pearl crescents are common in Hampton Roads and throughout the eastern United States and western states, according to Hamilton.