Bag Worm Treatment: All You Need to Know for a Healthy Garden

Bagworms are a common and pesky problem for many homeowners who take pride in their landscape. These caterpillars live their entire lives in tough, protective “bags” made of silk, feeding on foliage until the end of summer.

An infestation of bagworms can lead to unsightly damage to various types of trees, including arborvitae, red cedar, juniper, and spruce¹.

Knowing how to treat and prevent bagworm infestations is essential to maintaining a healthy and attractive landscape.

In this article, we’ll explore all you need to know about bagworm treatment, from identifying symptoms to taking effective action against these destructive pests. Stay tuned for valuable tips on keeping your trees and plants bagworm-free.

Bag Worm Lifecycle

Eggs and Hatching

Bagworms lay their eggs in protective silk bags during the fall, which hatch in spring. Each female bagworm can lay up to 500-1,000 eggs within the bag, ensuring a large population in the next season.

Larval Stage

As the tiny caterpillars hatch, they construct their own bags using silk and nearby host plant materials. The larvae remain in these bags while they feed on the leaves of various trees such as arborvitae, red cedar, and junipers.

• Bags made of silk and plant materials
• Larvae feed on various trees’ foliage

Larvae will continue growing and feeding throughout the summer months.

Pupa and Adult Stage

By late summer, bagworms enter the pupal stage within their bags. During this stage, they undergo metamorphosis and turn into adult moths.

Males transform into fully developed moths that can fly, while females remain underdeveloped, wingless, and do not leave their bags.

Males vs. Female Adult Bagworms:

Characteristic	Males	Females
Appearance	Fully developed moths	Underdeveloped, wingless
Movement	Can fly	Do not leave their bags

Males will then seek out the sedentary female bagworms for mating. After mating, the female’s lifespan ends, and she lays her eggs within the bag to start a new generation of bagworms. The adult males also die shortly after mating.

Identifying Bagworms and Infestations

Bagworms on Trees and Shrubs

Bagworms are common insect pests that affect trees and shrubs, particularly evergreens like junipers and arborvitae. They create cone-shaped bags using silk and bits of host plant materials.

Here are some common plants affected by bagworms:

• Arborvitae
• Juniper
• Pine
• Spruce
• Willow
• Oak
• Locust

Visible Damage to Plants

These pests can cause defoliation and visible damage in landscape plants, including deciduous trees. Bagworms consume leaves and needles, causing trees and shrubs to lose foliage.

Signs of bagworm infestation:

• Bags hanging from twigs
• Chewed or chewed off leaves
• Thinning of foliage
• Branch dieback

Comparison Table

Plant Type	Damage from Bagworms	Examples
Evergreens	Defoliation	Juniper, Arborvitae, Pine
Deciduous	Some leaf consumption	Oak, Locust, Willow

Bag Worm Treatment and Control Measures

Natural Predators and Biocontrol

Bagworms can cause significant damage to trees. One effective method to control their infestation is by leveraging their natural predators. Some common predators include:

• Birds
• Small mammals
• Insectivorous insects

For example, you can attract birds to your garden by providing nesting boxes and feeders. Another biocontrol method is using Bacillus thuringiensis (Bt), a natural bacterium that targets caterpillars and minimizes damage to beneficial insects.

Control Method	Pros	Cons
Natural Predators	Environmentally friendly	May not provide rapid control
Bacillus thuringiensis	Targets caterpillars specifically	May require multiple applications

Hand-Picking and Removal of Infested Plants

Hand-picking is another strategy for managing bagworm infestations. This involves:

• Inspecting your trees regularly
• Removing the bags manually as soon as you notice them

Bagworms tend to overwinter as eggs inside female bags, so it’s important to remove them during their dormant period to prevent further infestations.

Chemical Treatment for Bagworms

Proper Timing for Effective Treatment

To effectively treat bagworms with chemical control, proper timing is crucial. The ideal time to treat bagworms is during summer when they are still in their young larvae stage.

Bagworm eggs typically hatch in late May or early to mid-June, making this the prime time to initiate treatment.

Recommended Insecticides

Several effective insecticides can be used for bagworm control. These include:

• Malathion
• Carbaryl
• Diazinon
• Cyfluthrin

Insecticide	Pros	Cons
Malathion	Effective against bagworms	May be harmful if not used properly
Carbaryl	Fast acting	May be toxic to beneficial insects
Diazinon	Broad spectrum control	Restricted in some areas due to environmental concerns
Cyfluthrin	Low toxicity to mammals	Can be harmful to aquatic life

Keep in mind that chemical control should be applied to caterpillars early in the season. Late August and early September are not ideal times for treatment, as bagworms cannot be killed by pesticides at this stage.

Always follow label directions and safety precautions while using insecticides.

Preventative Measures and Maintenance

Regular Monitoring and Inspection

To prevent bagworm infestations, regularly inspect your plants for signs of feeding or defoliation. Caterpillars hide in sealed bags made of silk, making them challenging to spot.

Monitor your plants, especially those prone to infestations (e.g., arborvitae, red cedar, juniper, and spruce) between June and August, when the larval stage of bagworms is most active.

Keep an eye for additional plants that are at risk, such as black locust, elm, persimmon, honeylocust, poplar, and hemlock.

Keeping Your Garden Clean and Healthy

• Remove debris and dead leaves to limit the hiding places for bagworms.
• Encourage birds like sparrows that feed on bagworms by placing bird feeders near infested plants.
• Regularly prune your plants to maintain a healthy environment and prevent bagworms from finding attractive breeding spots.

One effective way to manage bagworm populations is hand-picking their bags from infested plants in October when they are sealed and less mobile.

Remove any egg sacks found during this time as well, taking care not to break them to prevent the next generation from emerging. Dispose of the bags away from your garden.

For larger infestations, consider using a sprayer with horticultural dish soap or specific insecticides like Orthene. However, chemicals should be a last resort, as they can harm beneficial insects and bacteria.

Keep in mind that weather can impact the mating and development of bagworms. Droughts may result in the earlier emergence of adult bagworms, while rainy conditions can delay their mating.

During the larval stage, female bagworms are fertilized by males and produce egg sacks. Regular monitoring and removing the bags can help prevent the next generation of bagworms from emerging and causing more damage.

Conclusion

To summarize, bagworms are insects that belong to the family Psychidae. They have worm-like bodies and make bags from plant materials and silk.

They are found in many regions of the world, where they feed on various plants, especially evergreens.

They can cause defoliation and death of plants if left unchecked.

You can control them by hand-picking, pruning, or using biological or chemical pesticides. Bagworms are pests that need to be treated to protect the health of plants.

Footnotes

1. Bagworm | Horticulture and Home Pest News ↩

Reader Emails

Over the years, our website, whatsthatbug.com has received hundreds of letters and some interesting images asking us about these insects. Scroll down to have a look at some of them.

Letter 1 – Bagworm

Strange leaf cocoon
Location: north side of house in Clifton VA (Fairfax)
September 13, 2011 12:51 pm
My husband took this photo today 9/12/11 at our home in Clifton, VA of a strang leaf cocoon located on a column in front of our door. It appears to be made of leaves. Can you identify it?
We have never seen it before.
On our front door I have 2 wreaths made of dry leaves that I think were used for this cocoon. It has been here for a few days.
Thanks much,
Signature: Camille W

Hi Camille,
This is the cocoon of a Bagworm.  Bagworms are caterpillars in the family Psychidae, and they begin to construct a bag from plant material when they are quite small, adding to the bag as they grow.  T

he Bagworms do not leave their bags, and eventually pupate in them.  Female Bagworm moths are flightless and legless.  The male mates with her inside the bag and she lays here eggs there as well. 

The female Bagworm truly never leaves her home.  You may read more about Bagworms on BugGuide.

Letter 2 – Bagworm

pls identify this ootheca(?)
March 13, 2010
I’ve been assuming/hoping this is a mantid ootheca, but it doesn’t look like any ootheca I’ve seen on the web. Is it a mantid ootheca or some less desirable creature? Found on a Japanese Maple tree in zip 43206. I want to hatch the mantids indoors to release in my garden…
Thanks! Tony
43206, Central Ohio, Urban micro climate

Hi Tony,
Theoretically, this is the cocoon of a Bagworm, a moth in the family Psychidae.  You may see additional examples and some species identifications on BugGuide. 

We wrote theoretically earlier because the female Bagworm is wingless, and she only crawls out of her cocoon to mate.  After mating, she returns to the cocoon and lays her eggs, so the cocoon may become an ootheca of sorts.

Thanks Daniel!  I guess I knew it wasn’t what I wanted or I wouldn’t have asked!?  At least now I know that I really do need to order a mantid ootheca.  You guys offer a great service to us laymen!  Thanks again.

Letter 3 – Bagworm

a little caterpillar with a traveling cocoon
Hi,
I’m hoping you can identify this little fellow. He’s been hanging around (literally) ,and under my blue ceramic bird bath. At first I thought he was building a cocoon, but he keeps crawling all over the place with it . Let me know, please, if you can identify him. His cocoon seems to be about 3″ long. I live in Parma, Ohio (a suburb of Cleveland). Thank you.
Mary Griffin

Hi Mary,
This caterpillar is a Bagworm. Bagworms are Moths in the family Psychidae. According to BugGuide: “Larvae (bagworms) construct spindle-shaped bags covered with pieces of twigs, leaves, etc., and remain in them, enlarging them as they grow, till they pupate (also in the bag). Adult females remain in the bag, emitting pheromones which attract adult males to mate with them.”

Letter 4 – Bagworm

Destructive Catepillar – NJ
Hi,
This Catepillar took down an Arborvite in a matter of days.  Their cocoons have blown all around in the wind and they are spreading fast.
Can you tell me what we are dealing with here, Southern NJ, zip 08086…
Kevin

Hi Kevin,
This is a Bagworm in the family Psychidae.  The caterpillars of the Bagworms construct a protective covering from plant material, generally the plant material that they feed upon. 

In the case of your photograph, that is probably the leaves of the Arborvite.  You can read more about Bagworms on BugGuide where the life cycle is briefly described as:  “Larvae (bagworms) construct spindle-shaped bags covered with pieces of twigs, leaves, etc., and remain in them — enlarging the bags as they grow — until they pupate (also in the bag). Adult females remain in the bag, emitting pheromones which attract adult males to mate with them. 

Eggs are laid inside the bag, and when they hatch the larvae crawl away to begin construction of their own individual cases.“

Letter 5 – Bagworm

bug that looks like dead hibiscus flower
Location:  Dallas/Ft. Worth Texas
August 10, 2010 9:09 pm
I found this caterpillar? slowly moving up my door jam in Texas and had never seen anything like it. Could you possibly identify it. I didn’t disturb it so I’m not sure if it is a flying or crawling bug. It moved up the door jam over several hours time. Thanks! Michele
Michele Bennett

Hi Michele,
This is a Bagworm in the family Psychidae.  Bagworms are moth caterpillars that fashion a bag from the foliage of the plants they feed upon.  Bagworms will migrate away from the food plant to find a suitable place for pupation, and they pupate inside the bag. 

The males of the species fly but the females are legless and wingless and do not leave the bag.  After mating, the eggs are laid inside the bag to begin a new generation.

Daniel,
Wow! Thanks for your quick response.  I was fascinated by “it” but now I realize I will need to kill it or it will continue to ruin my hibiscus plant right outside my front door.  Thanks again.  What a great site and service you have.
Michele

Letter 6 – Bagworm

Unknown bug on my car
Location:  Central Ohio
August 10, 2010 8:06 am
Hi my name is Vernoica Pence and I live in Hilliard Ohio. I came home from work and found an unknown bug on my boyfriends car. I have never seen a bug like this ever and I am an outdoor person. I was hoping if you could tell me what kind of bug it is.
Veronica Pence

Hi Veronica,
We are going to give you the part of the response we just gave Michele who wrote in with a related Bagworm.  This is a Bagworm in the family Psychidae. 

Bagworms are moth caterpillars that fashion a bag from the foliage of the plants they feed upon.  Bagworms will migrate away from the food plant to find a suitable place for pupation, and they pupate inside the bag.  The males of the species fly but the females are legless and wingless and do not leave the bag. 

After mating, the eggs are laid inside the bag to begin a new generation.  We actually believe your species is the Evergreen Bagworm, Thyridopteryx ephemeraeformis, which you may read about on BugGuide.

Letter 7 – Bagworm

Curious, spectacular cocoon
Location:  South Florida
September 1, 2010 9:15 pm
I found this in my crepe myrtle tree about two weeks ago. It’s a stunning piece of work, but I’ve never seen anything like it before.

Even my colleague, a caterpillar/moth/butterfly guru, has never seen the likes of it and pronounced it ”spooky.” It’s between 2-3 inches long. What made this?
wilmax

Hi wilmax,
This cocoon was made by a Bagworm, the caterpillar of a moth in the family Psychidae. 

As a caterpillar, the Bagworm spins a shelter from silk and organic matter from the plants upon which it feeds.  It drags the bag around while it feeds, never leaving its shelter.  It then uses the bag to pupate, the stage depicted in your photograph.  Adult Bagworm moths are sexually dimorphic. 

The males are winged and the females lack wings and legs and do not leave the shelter of the bag once mature.  After mating, the female lays her eggs in the bag and after hatching, the young caterpillars disperse, each spinning its own bag which is enlarged as the caterpillar grows.

Thank you!!  Thanks for choosing to feature the photo on the site. I see that you have had many similar questions in the past – I wish I had known where to start looking.