Native to the United States, the bagworm, Thyridopteryx ephemeraeformis, is a defoliating caterpillar in the order Lepidotera that commonly feeds on the foliage of many coniferous and deciduous trees east of the Rocky Mountains. The bagworm’s self- spun bag, which can be found hanging from the host plant by mid-summer is unsightly. Excessive feeding can strip away large quantities of leaves, causing branch dieback, and dead patches on the host plant.
Trees at Risk
Bagworms affect: arborvitae, fir, hemlock, juniper, pine and spruce, baldcypress, black locust, honeylocust, sweetgum and sycamore, boxelder, cotoneaster, maple, elm, buckeye, willow, crabapple, linden, poplar, and many more trees.
Signs of Damage
- Yellow spots on the foliage, usually in the upper portions of the tree, in late summer.
- Dead, open patches are common on coniferous hosts.
- 1-1/2 inch to 2 inch cone shaped bags hanging from tree branches by late summer.
- Often heavy defoliation by late summer.
Bagworms are difficult to control because they often go undetected until it is too late in the season to treat effectively. It is important to treat the larvae before they mature because young larvae are more sensitive to treatments. This means treatment is necessary in early spring to mid-summer. Picking bags off by hand can help to reduce populations, but is not always feasible. Look for bags during the winter to identify plants for treatment the following year.