Mature bagworm on Colorado blue spruce. (Photo submitted)
Mature bagworm on Colorado blue spruce. (Photo submitted)

Now is a good time to inspect trees and shrubs in your landscape for bagworms. Bagworms form small, 1-2” bags of dead plant material that are commonly found across Ohio and the Midwest. Bagworms often go unnoticed as their “bags” can be mistaken for cones that are commonly found on evergreen trees. Inside each bag resides a caterpillar.

Bagworms feed throughout the summer on over a hundred different types of trees and shrubs. They especially like arborvitae, juniper, spruce, and sycamore. Bagworms use a plant’s leaves or needles to create the “bag” that surrounds their bodies. These bags grow in size as the bagworms feed throughout the summer.

Within the next month, bagworms will stop feeding and “tie off” their bags with strong silken threads. These threads allow the bags to remain in place on twigs, branches, and other structures for several seasons. I have even seen them attached to the buildings and overhangs.

What happens inside the bag? Both male and female bagworms pupate and transform into moths. Male moths exit the bag and fly around seeking out female bagworms to mate. The female never leaves the bag but remains inside, lays up to 1000 eggs after mating, and dies.

The bags of female bagworms will hatch tiny caterpillars next spring, usually in early June. The caterpillars exit the bottom of the bag and spin a silken thread. The caterpillars are carried by the wind until they land on an object. If they land on a tree or shrub they may begin feeding. Otherwise they climb to the top of the object and allow the wind to carry them to another location.

What can you do now? Removing the bags by hand can effectively reduce the number of caterpillars emerging next year. Make sure hand-picked bags are placed in a sealed garbage bag or burned as the bagworms can move to other trees if dropped on the ground. If the bagworm numbers are too large, you can wait until next spring to use insecticides.

The best time to use insecticides to control bagworms is when the caterpillars are small and actively feeding, generally late June through early July. Insecticide options for bagworm control include Bt (Bacillus thuringiensis), carbaryl, cyfluthrin, spinosad, malathion, bifenthrin, permethrin, among others. Make sure to read and follow all label directions. Insecticidal sprays this time of year may control smaller bagworms that are still actively feeding, though larger bagworms may be unaffected.

For additional information, please contact the Putnam County Extension office at 419-523-6294, at scheckelhoff.11@osu.edu, or stop in at 1206 East Second Street in Ottawa. You can also find us on Facebook by sear