Sasha CampbellBagworms can cause serious damage to trees and shrubs. They are often found on evergreen plants, but they may also feed on some leafy trees.
You may also see small cases moving across walls or hanging from ceilings inside your home. People often call these pests plaster bagworms. However, outdoor bagworms and plaster bagworms are not the same insect.
This guide explains how to identify both pests. It also covers natural ways to control them outdoors and inside your home.
What Are Bagworms?
Outdoor bagworms are the caterpillars of moths in the Psychidae family. The common bagworm, Thyridopteryx ephemeraeformis, is a serious pest of many trees and shrubs in the eastern United States.
These caterpillars build protective bags around their bodies. Each bag is made from silk and small pieces of the plant on which the caterpillar feeds.
Plaster bagworms are different. Their correct name is household casebearers. They belong to the same moth family as clothes moths—not the true bagworm family [1].
Household casebearers usually live in warm, humid areas. They may appear on walls, ceilings, in garages, or inside closets.
Damage Caused by Outdoor Bagworms
Outdoor bagworms feed on the leaves and needles of many plants. Some of their favorite hosts include:
- Arborvitae
- Cedar
- Juniper
- Pine
- Spruce
- Cypress
They may also feed on maple, sycamore, boxelder, linden, and other leafy trees.
Large numbers of bagworm caterpillars can strip a plant of its leaves or needles. Heavy feeding can cause lasting damage to evergreens. In some cases, a badly infested evergreen may die [2].
Leafy trees often recover more easily because they can grow new leaves. However, repeated attacks can weaken them.
Household casebearers do not feed on garden plants. Indoors, they eat old spiderwebs, hair, wool, feathers, dead insects, and other natural materials.
How to Identify Outdoor Bagworms
Outdoor bagworm cases may look like small pine cones hanging from a plant. They are often gray, brown, or green.
Each case may contain pieces of leaves, needles, bark, or twigs. This covering helps the insect blend in with the plant.
Young bags are very small and easy to miss. As the caterpillar grows, its case may reach 1 to 2 inches long.
The caterpillar sticks its head and legs out of the bag to feed. It drags the bag with it as it moves.
By late summer, the caterpillar attaches the bag firmly to a twig. It then changes into an adult inside the bag.
Only the adult male becomes a winged moth. The male is dark and hairy, with a wingspan of about 1 inch.
The adult female has no wings. She stays inside her bag, where mating takes place.
After mating, the female lays hundreds of eggs inside the bag. The eggs remain there through winter and hatch the following spring. One female bag may contain 200 to 1,000 eggs [2].
How to Identify Plaster Bagworms
Plaster bagworm cases are much smaller than outdoor bagworm cases. A full-grown case is usually about ⅓ to ½ inch long.
The case is flat and shaped somewhat like a pumpkin seed. It is usually gray or brown and is open at both ends.
The larva can turn around inside its case. It pushes its head and legs out of either end when it wants to move or feed.
You may find these cases:
- On walls and ceilings
- Under furniture
- Near light fixtures
- Inside closets
- In bathrooms
- In garages or sheds
- Near old spiderwebs
- On wool rugs or curtains
Adult household casebearers are small gray or brown moths. Some females have up to four spots on their front wings.
If you are unsure which pest you have, take clear pictures and send them to your local Extension office or a pest expert.
When to Control Outdoor Bagworms
Timing is very important.
Hand-picking works best from fall through early spring. During this time, the eggs are still inside the attached bags.
Sprays work best after the eggs hatch and while the caterpillars are young. This often happens in late spring or early summer, but the exact time depends on your climate.
Small caterpillars are easier to kill because their protective bags are still small. Once the caterpillars and their bags grow larger, sprays may be less effective.
How to Get Rid of Outdoor Bagworms Naturally
The following methods can help you control outdoor bagworms.
1. Hand-Pick the Bags
Hand-picking is one of the best ways to control a small outdoor infestation.
Check affected trees and shrubs carefully. Cut or pull each bag from the plant. Pay close attention to the undersides of branches and areas near the trunk.
Do not leave the bags on the ground. Some may contain eggs that can hatch later.
Drop the bags into a bucket of soapy water. You can then place them in a sealed bag and throw them in the trash.
Try to finish hand-picking before the eggs hatch in spring.
2. Inspect Nearby Plants
Young bagworm caterpillars can spread to nearby plants. They release strands of silk that allow the wind to carry them.
After finding bagworms on one plant, inspect nearby trees and shrubs. Look closely at evergreens because the bags can blend in with the needles.
Check fences, walls, outdoor furniture, and other surfaces, too. Bagworms may attach their cases to these places before becoming adults.
Continue checking the area every week while the caterpillars are active.
3. Prune Dead or Badly Damaged Branches
Bagworms may leave some small branches dead or badly damaged. Prune these branches after removing the bags you can reach.
Place infested branches in a sealed yard-waste bag. Do not leave them near healthy trees.
Avoid removing a living branch simply because it has a few bags. Hand-picking is usually better in that situation.
Do not remove so much growth that you weaken the plant. If a large tree is badly damaged, ask a certified arborist for help.
4. Use Btk
Bacillus thuringiensis subsp. kurstaki, or Btk, is a naturally occurring bacterium. It controls certain young moth and butterfly caterpillars.
When a young bagworm eats treated foliage, Btk affects its digestive system. The caterpillar stops feeding and later dies.
Btk works best when bagworms are small. It becomes less effective as the caterpillars and their bags grow larger. More than one treatment may be needed [2].
You can buy Btk in spray or powder form at some garden centers or online.
Follow the product label carefully. Spray only the affected plants because Btk can also kill young butterfly and moth caterpillars feeding on treated leaves.
5. Apply a Labeled Spinosad Product
Spinosad is made from substances produced by a soil bacterium. Some spinosad products are approved for use in organic gardens.
Choose a spinosad product that lists bagworms and the affected plant on its label.
Spray while the bagworms are small and actively feeding. Spinosad becomes less effective against larger bagworms [3].
Although spinosad comes from a natural source, it can harm bees while the spray is wet. Do not spray open flowers. Apply it late in the day when bees are less active, and follow all label directions.
6. Try a Labeled Neem or Azadirachtin Product
Neem-based pesticides may help control young bagworm caterpillars. Azadirachtin, a substance taken from neem seeds, can slow feeding and growth in some insects.
Choose a neem or azadirachtin product that lists bagworms or caterpillars on the label. The label must also allow use on the type of plant you want to treat.
You can find neem products at garden centers or online.
Do not use a homemade mixture with a set amount of neem oil and household soap. Neem products come in different strengths. Too much oil or soap may burn plant leaves.
Test the product on a small part of the plant first. Do not spray during very hot or sunny weather.
7. Protect Helpful Insects
Tiny parasitic wasps and other natural enemies attack outdoor bagworms. These helpful insects may reduce bagworm numbers over time.
Avoid using broad insect killers when they are not needed. These products may kill helpful insects along with the pests.
You can also grow flowering plants near affected trees. Asters and daisies may provide food for some of the helpful insects that attack bagworms [4].
Do not depend on purchased Trichogramma wasps as your main treatment. There is not enough reliable guidance showing that home releases will control common bagworms.
8. Welcome Insect-Eating Birds
Several kinds of birds eat bagworms. Finches and other insect-eating birds may pull apart the bags and eat the insects inside [5].
You can attract insect-eating birds by growing native plants and providing clean water. Shrubs and trees can also give birds places to rest and nest.
Birds may help reduce pest numbers, but they will not always stop a large infestation. Combine this method with hand-picking or another suitable control.
How to Get Rid of Plaster Bagworms Indoors
The following steps can help control plaster bagworms, also called household casebearers, inside your home.
9. Vacuum Indoor Cases
Vacuuming is one of the easiest ways to remove household casebearers.
Use the hose attachment to collect cases from walls, ceilings, corners, closets, and garages. Also vacuum under furniture and around light fixtures.
Some of the cases you see may be empty. However, removing all of them helps you notice if new ones appear.
Empty the vacuum outdoors when you finish. Place the contents in a sealed bag before putting them in the trash.
10. Remove Spiderwebs and Indoor Debris
Household casebearers often feed on old spiderwebs and the dead insects caught in them. They may also eat hair, lint, feathers, and other natural materials.
Clean corners, baseboards, closets, shelves, and areas behind furniture. Sweep or vacuum away spiderwebs and dead insects.
Regular cleaning removes the insects and much of their food. UF/IFAS reports that hand-picking, vacuuming, and removing spiderwebs are usually enough to control household casebearers [1].
11. Lower Indoor Humidity
Household casebearers prefer warm, humid places. They are often more common in bathrooms, garages, carports, sheds, and rooms without air conditioning.
Use fans, air conditioning, or a dehumidifier when possible. Repair leaking pipes and improve airflow in damp rooms.
Lowering humidity will not remove every case at once. However, it can make your home less suitable for these pests.
12. Clean and Protect Natural Fabrics
Household casebearers sometimes feed on wool, silk, feathers, and other materials that come from animals. Damage to clothing is not common, but it can happen.
Wash or dry-clean affected items as directed on the care label. Vacuum rugs, closets, and fabric storage areas.
Store clean wool, silk, and feather items in sealed containers. Do not place dirty clothing into long-term storage. Sweat, hair, and skin oils may attract fabric pests.
Mississippi State University Extension notes that cleaning and vacuuming are usually enough for household casebearers found in rooms and storage areas [6].
Can You Prevent Bagworms?
You may not be able to prevent every bagworm. However, regular inspections can stop a small problem from becoming a large one.
Check vulnerable trees in fall, winter, and early spring. Remove any attached bags before the eggs hatch.
During late spring and early summer, look for tiny moving bags and new feeding damage. Treating young caterpillars is much easier than treating large ones.
Keep trees healthy by watering them during dry weather. However, do not overwater them. Add mulch over the root area, but keep it several inches away from the trunk.
Indoors, vacuum often, remove spiderwebs, lower humidity, and protect wool or silk items in sealed containers.
Takeaway
Outdoor bagworms and plaster bagworms are two different pests.
Outdoor bagworms feed on trees and shrubs. Hand-picking is the best choice when the bags are easy to reach. Btk, spinosad, and certain neem products may help when young caterpillars are actively feeding.
Plaster bagworms, or household casebearers, live indoors and feed on spiderwebs and other natural materials. Vacuuming, cleaning, and reducing humidity are usually the most useful controls.
Identify the pest first. Then choose a method that matches where it lives and what it eats.
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