How to Get Rid of Bagworms
Dream Debrief
- Bagworms are caterpillars, not worms: They build protective silk bags covered in plant debris and feed on the foliage of trees and shrubs, especially evergreens.
- Timing is everything: The treatment window runs from late May through early July. After late August, insecticides stop working entirely.
- Hand removal works for small infestations: Picking bags off in fall or winter before eggs hatch in spring reduces next year's population significantly.
- Arborvitae, juniper, and spruce are most at risk: Evergreens can't regrow lost needles, so a bad infestation can permanently damage or kill the plant.
- One missed bag can restart the problem: Each bag can hold up to 1,000 eggs. Thorough removal matters.
Bagworms are easy to miss until they've already done serious damage. Their bags blend in with plant foliage and get mistaken for pinecones or dead growth. By the time most homeowners notice them, the feeding season is nearly over and treatment options are limited. Knowing what to look for and when to act makes the difference between a manageable problem and a dead arborvitae.
What Bagworms Look Like
Bagworms build spindle-shaped cases from silk, twigs, and bits of foliage from the plant they're feeding on. The bags start small, around 1/8 inch, and grow to about 1.5 to 2 inches as the caterpillar matures. They hang from branches and blend in well enough that they're regularly confused with pinecones or dead plant matter.
To confirm bagworms, look for bags that are uniform in shape, hanging from twigs or branches rather than growing from the plant. Gently disturb one in late spring or early summer and a small caterpillar head may poke out from the top. Later in the season the caterpillar will have sealed itself inside to pupate.
Trees and Shrubs Most at Risk
Bagworms feed on over 120 species of trees and shrubs, but evergreens take the worst damage. Unlike deciduous trees, evergreens can't regrow lost needles. A heavy infestation on an arborvitae or juniper can kill branches outright or take out the entire plant over a couple of seasons.
The most commonly affected species include:
- Arborvitae
- Juniper
- Spruce
- Pine
- Cedar
- Cypress
- Oak, maple, and other deciduous trees (less common but still at risk)
If you have arborvitae or juniper in your landscaping, those are the first plants to check.
Life Cycle and Why Timing Matters
Getting rid of bagworms comes down to acting at the right point in their life cycle. Miss the window and your options shrink fast.
Fall to early spring
Eggs overwinter inside bags on the plant. Hand removal during this window eliminates the following year's population before it starts.
Hand removal onlyLate May to June
Eggs hatch and larvae begin feeding. Bags are tiny, caterpillars are small, and bio-based treatments like Bt and Spinosad work well.
Best treatment windowJune through July
Larvae continue feeding and bags grow larger. Treatment still works but requires stronger pyrethroid-based products.
Treatment still possibleLate July through August
Caterpillars seal their bags to pupate. Insecticides stop working entirely. Most homeowners notice the damage at this point.
Too late to sprayMost homeowners notice bagworms in late summer when the damage becomes obvious, which is exactly when treatment stops working. The goal is to catch them in May or June before they've had time to do much damage.
How to Remove Bagworms by Hand
For smaller infestations or as a late-season option, hand removal is worth doing. Cut or pull the bags from the plant and drop them into a bucket of soapy water to kill the insects inside. Don't toss them on the ground nearby; they'll climb back up and resume feeding.
The best times to hand-remove:
- Fall through early spring: Before eggs hatch in late May. Removing bags during this window eliminates overwintering eggs and reduces the following year's population.
- Late summer: After feeding has stopped and caterpillars have sealed their bags. Insecticides won't work at this point, but physical removal can still clear the bags before eggs hatch next spring.
Hand removal is practical for accessible, smaller trees and shrubs. For larger trees or heavy infestations, it's not realistic on its own.
How to Treat Bagworms
If you catch the infestation during the active feeding window, insecticide treatment is effective. The right product depends on when you're treating.
May through June
Bio-based: Bt or Spinosad
Works well on small caterpillars and has a lower impact on surrounding plants and beneficial insects. This is the preferred window for treatment.
Mid to late summer
Pyrethroid-based insecticides
More effective against larger larvae, though results are less consistent. Two applications spaced two weeks apart may be needed for heavy infestations.
After late August
No insecticide is effective
Once caterpillars have sealed their bags, spraying won't work. Hand removal is the only option until the following spring.
How to Prevent Bagworms
If bagworms have been a problem before, they'll likely come back. Bagworm eggs overwinter on the plant and hatch the following spring. Larvae can also balloon on silk strands and drift in from neighboring trees and properties, so a well-maintained yard isn't fully protected from new infestations.
The most reliable prevention steps:
- Inspect susceptible trees in late winter and early spring for overwintering bags
- Remove any bags found before late May when eggs hatch
- Schedule a preventive treatment in late May or early June if you've had repeated problems
- Keep trees healthy through consistent watering and mulching; healthy plants recover better from defoliation
Professional Tree and Shrub Care
The treatment window for bagworms is narrow and easy to miss. Most homeowners notice the bags in late summer when the damage is already done, and effective treatment is no longer an option. A professional tree and shrub program handles inspection and treatment timing so you're not reacting after the fact.
DreamLawn's tree and shrub care service covers bagworm treatment, along with monitoring for other common pests and diseases that affect landscape plants. If your arborvitae, juniper, or other trees are showing signs of damage, reach out for an assessment.