Bag Worms

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 chemical treatments. Treatments in May/Early June are most effective for treating bag worms, but they can be treated throughout the Summer months as well.

Picking bags off by hand can help to reduce populations but is usually not feasible for commercial companies. Look for bags during the winter to identify plants for treatment the following year. 

Below is some information on what trees are susceptible hosts, what bagworm damage looks like and more:

Susceptible Hosts

Several Species Including: 

  • Arborvitae (Thuja)
  • Fir (Abies)
  • Baldcypress (Taxodium)
  • Honeylocust (Gleditsia triacanthos)

Signs of Damage

  • Initial feeding damage on evergreen trees causes branch tips to appear brown and unhealthy. 
  • Branch decline on severely infested twigs.
  • Stripping of foliage, usually in the upper portion of the tree, in late summer. 

Physical Appearance 

  • Egg: Yellowish, cylindrical in shape and laid in mass. 
  • Larva: Dark brown and ¾-1” long with black spotted heads. Larva bags are generally 1 ¼  to 2 inches long. 
  • Pupa or “Baby Bagworms” are dark brown/black and will remain in the bag. 
  • Male bagworm moths are sooty black with a densely hairy body, clear wings, and a wingspread of about 1 inch. Female adult bagworms are soft-bodied and grub-like, and are yellowish-white in color with no functional legs, eyes, or antennae. 

Life Cycle

  • Eggs hatch in late spring and young larvae emerge, construct a silklike bag about ⅛ inch long around its body, and begin feeding on plant tissue. 
  • The larvae continue to feed into midsummer until pupation begins. As the larvae feed and grow, the bag enlarges. Pupation lasts two to three weeks. 
  • By late summer the male adults emerge from the bag and mate.
  • The females remain in the bag. After mating the female encases the egg mass, and remains in place until spring. 
  • One generation per year.

Don’t wait before they hatch. 

Specialty Tree Service now has an application that is systemic and can be done prior to hatching. This is a soil injection and requires no spraying, so no fear of spray drift from wind, complaints from any neighbors, and harming bees that might be pollinating.

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