A friend asked for help in identifying a plant growing on her property. She thought it was a milkweed, and she was excited at the prospect that it might attract Monarch butterflies. Milkweeds are the only food plants on which Monarch caterpillars can thrive. Monarch numbers have declined steeply in the past few years, largely due to loss of habitat and their caterpillar food plants, the milkweeds.
The plant in question turned out to be a dogbane, a species commonly called Indian Hemp (Apocynum cannabinum). There is a closely related species called Spreading Dogbane (Apocynum androsaemifolium), but Indian Hemp is the species I see most often. These two species also interbreed.
It’s easy to understand how my friend was fooled, since Indian Hemp and the other dogbane species resemble milkweeds. You might even say there is a family resemblance, since milkweeds are in the Dogbane (Apocynaceae) family. Both have simple, opposite, untoothed oval leaves with a strong midvein, and look similar at a glance.
My friend, disappointed that the plants weren’t a milkweed species, asked ‘What good is dogbane?’.
Plenty, as it turns out. It’s a great source of nectar in early summer, before many other species start blooming. The US Department of Agriculture – Natural Resources Conservation Service (USDA NRCS) ranks Indian Hemp’s value to pollinators as ‘very high’. Many bee species are frequent visitors to Indian Hemp, feeding on both nectar and pollen.
Butterflies also visit Indian Hemp for its nectar.
Many other beneficial insects can be found feeding on Indian Hemp. Adult Pennsylvania Leatherwings (Chauliognathus pensylvanicus), sometimes called Goldenrod Soldier Beetles, are known for foraging on goldenrods for pollen, but they visit a variety of other flowers, including Indian Hemp. Their larvae prey on the eggs and larvae of other insects, helping to keep those other insect populations in check.
Tachinid flies may visit Indian Hemp for nectar. These beneficial critters lay eggs on nymph or adult insects, some of which are harmful to crops or to plants in general, including stink bugs, squash bugs, and even Gypsy Moths and Japanese Beetles. Their larvae live inside these host insects, feeding on their insides. This prevents the victimized insects from reproducing, and ultimately kills them. (Science fiction writers, eat your hearts out!)
Small Milkweed Bugs (Lygaeus kalmii) are primarily seed eaters, but they have a broader palate than their name implies. The adults feed on a variety of food sources, including nectar from many flowers such as the dogbanes.
When Dogbane flowers are pollinated, they produce a pair of fruits, reflecting the structure of the flowers’ reproductive parts. Each flower has two ovaries, and each ovary produces one fruit called a follicle, a dry (not fleshy) fruit that splits open along one seam to release the many seeds inside. Small Milkweed Bug nymphs feed on dogbane seeds in addition to milkweeds, as well as the seeds of some other plants.
Dogbanes even have a beetle named after them, the Dogbane Beetle (Chrysochus auratus). This insect feeds primarily on various parts of plants in the Dogbane family throughout its life cycle. It’s appearance is often compared to that of the Japanese Beetle, but it’s much more beautiful, with distinctive iridescent red, blue-green and copper coloring.
Dogbanes are among the food plants used by the caterpillars of the Snowberry Clearwing moth,
and of the Delicate Cycnia, also called the Dogbane Tiger Moth (Cycnia tenera).
Like the milkweeds, dogbane stems contain fibers that can be used to make rope. The common name Indian Hemp is based on the fact that this species is a particularly good source for these fibers, and were used by Native Americans for this purpose.
Birds take advantage of these fibers and the fluff from dogbane seeds for nest-building, just as they do with the fibers and seed fluff from milkweeds. (See Milkweed – It’s not just for Monarchs.)
Dogbanes share some of the chemical compounds, including cardiac glycosides, that make milkweeds indigestible or toxic to many herbivores that would otherwise eat them. These chemicals are especially potent in Indian Hemp. A few sources (Natural History Museum; The Book of Swamp and Bog by John Eastman) say that Monarchs may use Spreading Dogbane as a caterpillar food plant. Since the protection offered by sequestering these chemicals in parts of their bodies is the reason Monarchs have evolved to specialize on Milkweeds, maybe they can evolve to use dogbanes, too. Have you ever seen a Monarch caterpillar on a dogbane? (I haven’t, but I’ll keep looking!)
Even without Monarchs, dogbanes are pretty productive plants!
Eastman, John. The Book of Swamp and Bog. 1995.
Eaton, Eric R.; Kauffman, Ken. Kaufman Field Guide to Insects of North America. 2007.
Elpel, Thomas J. Botany in a Day. 2006.
Evans, Arthur V. Beetles of Eastern North America. 2014.
Rhoads, Ann Fowler; Block, Timothy A. The Plants of Pennsylvania of Pennsylvania. 2007.
Attracting Beneficial Bugs
Small Milkweed Bug:
Illinois State Museum