How Do You Kill Bagworms?

How to Kill Bagworms

What are they? 

Bagworms are actually a type of moth. They create a very distinct spindle-shaped bag which resembles a small pine cone. Bagworm eggs will overwinter in these bags attached to branches by a silk thread. There can be well over 500 eggs inside a single bag! So what factors cause bagworms to show up in your landscaping, and how can you get rid of bagworms for good? We have a few suggestions…

Caterpillars in the bag

When the larvae hatch and emerge from the bag in the spring, they feed on the host plant for about six weeks. Each of these caterpillars creates their own bag from silk and bits of plant material. The bag starts out at about a quarter of an inch long, and typically by the end of the summer reaches a length of 2″.

​Females will basically stay in this bag their whole life, even after pupation. Males will emerge to mate as a small moth with clear wings. After mating, the female bagworm will lay her eggs in the bottom of the bag and then die, starting the cycle over again.

What plants do bagworms eat?

Bagworms can eat quite a few different types of trees and shrubs. 128 different varieties actually! Generally, though they are found on conifers. Leyland cypress and junipers seem to be some of their favorites here in Virginia, but they can feed from other cypress varieties, pines, spruce, arborvitae, and even cedars.

​If left unchecked, they will defoliate the host plant, often resulting in the death of the tree or shrub because it becomes too weak.

Distinct Spindle-Shaped Bags

How do I get rid of bagworms? 

Because there are many eggs per bag, bagworms can and will spread extremely quickly. If you notice them, it is very important to take care of the problem right away. Here are a few options.
  • The most effective bagworm removal strategy
Handpicking is by far the best way to control them. It’s simple, and can be done with no toxic insecticides. Once picked, the “bags” should be soaked in a bucket of soapy water to suffocate the eggs. 
  • Organic bagworm spray
In some situations, handpicking may be too time consuming or impractical if the worms are attached to high branches. Bacillus thuringiensis is a naturally occurring bacteria found in the soil, and is available in powder or spray form. Bacillus thuringiensis contains a protein that is toxic to bagworms, but generally safe to other wildlife. You will need to time your application with the emergence of the larva- typically this happens in June. Often, you will need to repeat the application a few times about a week apart for effective control.
  • Preventing bagworms with dormant oil
Dormant Oil can be used to control bagworms, but it does not have a 100% success rate. Oils work by suffocating the pests, forming a coating on their body and blocking their ability to breath. Using oil before bagworms appear usually is a good idea to stay ahead of the problem. Oil can also help control other pests like scale or mites.
  • Why you shouldn’t use insecticide
There are plenty of insecticides that will do the trick. However, I recommend avoiding these at all costs, as they will cause harm to other insects in the vicinity.
How to Prevent Bagworms