Caterpillars are Eating My Monarda

Butterflies and Moths That Visit Monarda

• The various types of Monarda attract a wide variety of moths and butterflies, including the Painted Lady, Milbert's Tortoise Shell and Mourning Cloak butterflies and Eastern Tiger swallowtails. In most cases, Monarda serves as a nectar plant for these creatures -- meaning they do not lay their eggs on the plants, and their caterpillars feed off of other plants. The caterpillars of some types of hummingbird moths use Monarda as a food source. These include the Hermit Sphinx (Sphinx eremitus or Lintneria eremitus), the Pyralid moth (Pyrausta orphisalis) and the Gray Marvel (Agripodes teratophora), according to the Illinois Wildflowers website.

Caterpillars of Concern

• Hermit Sphinx caterpillars are night feeders. Look for them near the base of the plant, where they hide during daylight hours, according to the Restoring the Landscape with Native Plants website. The caterpillars are dark gray with a prominent black spot on their heads. This spot is surrounded by a paler, tan/yellow color.

  The caterpillars of the Pyralid moth or Orange Mint moth may silk together leaves on plants they populate. This moth produces several generations per year, and its caterpillars feed from May to October, notes the Oregon State University Integrated Pest Management on Peppermint website. The caterpillars have two dark brown- or black-colored lines visible along their backs, running the length of their bodies. Their bodies may be orange, green or yellow in color.

  Monarda serves as a host plant for the larval and caterpillar forms of the Gray Hairstreak. The butterfly deposits its eggs on Monarda flowers. When the caterpillars are young, they eat the flowers of the plant, and as the caterpillars mature, they move to feed on the plant's leaves. Gray Hairstreak caterpillars come in a wide range of colors, but the long hairs of the thick-bodied larvae make them easy to identify. The Bugguide notes that these caterpillars may be attended by ants.

Treatment

• Remove caterpillars by hand if you find them on your plants. Sticky cards and pheromone traps placed near your plants can catch adults before they lay eggs. The microbial insecticide Dipel (Bacillus thuringiensis var. kurstaki) is used to control caterpillars, and natural enemies of caterpillars such as parasitic wasps may help reduce their populations.

Considerations

• The caterpillar stage lasts only a week to 10 days. Nearby weeds may serve as cover and a nectar source for adults, so weed control can help control butterfly and moth populations. In most cases, the creatures visiting your plants will not be of a harmful type. Traps and insecticides may kill harmless moths and butterflies along with the ones that feed on your Monarda, so consider relocating any caterpillars you find or sacrificing a few flowers for a few lovely butterflies and showy moths.