Like last year, we are currently experiencing what has been described by OSU's State Extension entomologist as a "bumper crop" of bagworms.
The common bagworm - Thyridopteryx ephemeraeformis - is found most in its larval, or baby, form. The insect larva creeps around and feeds on tree foliage while living inside of a bag that is constructed from foliage and other tissues. Adult males are small moths with a wingspan of about an inch. Adult females are wingless and retain many features of the larvae. Bagworms are a native species found in most states east of the Rocky Mountains.
Eggs survive the winter in bags and begin to emerge in April or May each year. These young larvae feed and construct bags immediately.
They begin around one quarter of an inch long and can reach 2 inches long before wintertime. In late summer, adult males leave their bags as moths in search of adult females who have remained in their bags. They mate, and as a result, 500-1,000 tiny eggs will be left inside the bag. In Oklahoma, the most common hosts are eastern redcedar - Juniperus virginiana, arborvitae - Thuja spp., and other junipers. Some will feed and live on other species, such as sycamore and willow.
Damage to host plants can be severe and can cause death if there is no attempt at pest control. Evergreens do not produce new foliage each year, so recovery from damage can take years of management. Infestations can be reduced by removing the bags by hand and burning them.
Do not attempt to climb ladders to reach upper canopy populations; contact an International Society of Arboriculture certified arborist for help. Chemical controls are most affective if applied before early June. Products such as Bt spray or Spinosad can be used then. Large larvae, like we are seeing now, should be controlled with products that contain carbaryl (Sevin) or malathion.
It is important to understand that bagworms exist within a food web where they are the prey of certain species of wasps. It is expected for them to have heavy and light population years. We do not know when the population counts of bagworms will decrease, but for now, happy picking and burning!
Contact the Cherokee County OSU Extension office at (918) 456-6163 for questions.
Garrett Ford is an agriculture educator for the Cherokee County OSU Extension office.