An interesting caterpillar was reported this spring feeding on a number of different perennials, including coreopsis, Rudbeckia, New England aster, and Echinacea (coneflower). These caterpillars were first reported during early June, although they probably hatched sometime in late May. The caterpillars feed until mid-June when they pupate. They are expected to emerge as adults later this summer.
These caterpillars grow to be a little over an inch long. They are black with tufts of spines on each body segment. As they grow larger, they develop a tannish stripe down the sides of their body. Although a pest in your garden, these caterpillars grow up to be an attractive nymphalid (brush-footed) butterfly, probably a species of checkerspot butterfly. In most cases, feeding in gardens is not severe and you can ignore small or moderate numbers.
If caterpillars are abundant, they can cause significant defoliation. If you need to manage these caterpillars, you have several options. You can handpick them and toss them into a bucket of soapy water. Although the spines are dangerous looking, they are not irritating to the touch. You can also apply an insecticide if necessary. There are many contact products that would be effective. Examples of less toxic options include, insecticidal soap, Bacillus thuringiensis, and spinosad. Treat as soon as you notice the caterpillars when insecticides are generally more effective and to minimize plant damage.
Published in Yard & Garden Line News, July 1, 2004