Bagworm on arborvitae. Photo courtesy Purdue University
West Lafayette, Ind. — Relatively mild Indiana winters over the last several years have caused bagworm infestations to spread northward across the state, said a Purdue University entomologist.
“Typically, bagworms were found in the southern part of the state,” said Cliff Sadof. “The last 10 winters have been somewhat mild, causing infestations to spread farther north and increase in severity throughout the state.”
These caterpillars, named for their habit of living in leaf-covered bags, are most commonly found in dense plantings of evergreen spruces, pines and arborvitae. They damage these trees by stripping their leaves.
“Homeowners who had their trees defoliated by bagworms last year should be preparing themselves and scouting their trees for this year’s crop of pests,” Sadof said. “There are two ways to determine whether or not a bagworm infestation has survived. The easiest way is to wait until eggs have hatched and inspect host plants for small bagworm caterpillars feeding on leaves.”
These insects emerged in Evansville in mid-May and will emerge in early June in central Indiana and mid-June in the northern part of the state.
“The second way to determine whether or not a bagworm population survived the winter is to cut open the bags to reveal the body of the female,” he said. “Break apart the female and examine the eggs. If the eggs are creamy white, they are viable and will hatch into caterpillars. People in communities affected by bagworms have been learning just how important it is to inspect their trees in the month of June,” Sadof said.
“Doing so can help them identify infestations earlier and control them with insecticides before too much defoliation occurs.”
For homeowners who haven’t experienced bagworm issues in the past, Sadof said inspecting trees in late June for new infestations is a good idea.
“New infestations start in June, but symptoms won’t likely start until a month has passed,” he said.
Here’s a Purdue Extension publication that give tips for controlling bagworms, including some biological or natural products.
