Bagworm

📐 FIELD GUIDE ILLUSTRATION

Original illustration by PestControlBasics.com. Use the labeled features above to confirm your identification.

🔬

PestControlBasics Editorial Team

Reviewed by Derek Giordano · Updated 2026

🔍 Identification

Bags: 5-8cm (mature); elongated; covered with foliage bits, twigs, and silk — resembles a small pine cone. Caterpillar feeds by extending its head from the bag opening while dragging the bag. Found on: arborvitae, juniper, spruce, pine, and many deciduous trees. Females: wingless, never leave the bag; lay 500-1,000 eggs inside bag in fall. Young larvae: tiny bags, visible in June — most vulnerable stage.

🧬 Biology & Behavior

Eggs overwinter inside old bags, hatching May-June. Young larvae (1st-2nd instar) are highly susceptible to Bt kurstaki through June. By late July, caterpillars are large, bags are half-developed, and chemical control is much less effective. One generation per year. Arborvitae can be killed in 1-2 seasons of heavy infestation.

⚠️ Damage & Health Risk

Progressive defoliation; arborvitae killed in 1-2 seasons of heavy infestation; significant hedge and specimen tree loss; limited natural enemy control.

🔧 DIY Treatment

Hand-remove bags in fall through winter — each bag removed eliminates 500-1,000 eggs. Bt kurstaki spray in June when bags are tiny — this is the critical window. After July 4th, chemical control becomes much less effective.

👷 When to Call a Pro

Emamectin benzoate trunk injection for severely infested valuable arborvitae.

❓ FAQ

When is the best time to spray for bagworms?

June — when bags are 1cm or smaller and larvae are in early instars. Bt kurstaki is highly effective on young caterpillars but zero effect on eggs or large caterpillars. After July 4th, chemical control becomes much less effective as caterpillars mature inside their protective bags.

Can I pull bagworm bags off by hand?

Yes, and it's highly effective. In fall and winter, pull every bag you can reach and destroy them (don't drop on ground — eggs still hatch). Each bag removed eliminates 500-1,000 eggs next spring. Combine fall hand-removal with June Bt spray for comprehensive management.

Factor	Details
U.S. Range	All or most U.S. states
Regional Detail	Distribution varies — consult your local extension service for regional prevalence data.

Factor

Details

U.S. Range

All or most U.S. states

Regional Detail

Distribution varies — consult your local extension service for regional prevalence data.

📅 Treatment Timing Guide

Treating at the right time dramatically improves results. Pest control timed to the life cycle uses less product and achieves better long-term control.

Period	Action
Spring	Inspection and perimeter treatment before pest season starts.
Summer	Active monitoring and targeted treatments as needed.
Fall	Preventive treatment before overwintering pests seek entry.

Period

Action

Spring

Inspection and perimeter treatment before pest season starts.

Summer

Active monitoring and targeted treatments as needed.

Fall

Preventive treatment before overwintering pests seek entry.

💰 Professional Treatment Costs

Service Type	DIY Cost	Professional Cost
Initial inspection	Free (self-inspect)	$75–$150 (often credited to treatment)
One-time treatment	$30–$100 in materials	$150–$500
Annual service contract	N/A	$400–$900/year
Severe infestation	Often ineffective alone	$500–$2,500+

Service Type

DIY Cost

Professional Cost

Initial inspection

Free (self-inspect)

$75–$150 (often credited to treatment)

One-time treatment

$30–$100 in materials

$150–$500

Annual service contract

N/A

$400–$900/year

Severe infestation

Often ineffective alone

$500–$2,500+

Prices vary by region, property size, and infestation severity.

❓ Common Questions About 🐛 Bagworm

How do I confirm I actually have this pest (not something similar)?

The most reliable confirmation is a physical specimen — capture one and compare to reference images on this page. For cryptic pests (bed bugs, termites), look for secondary signs: frass, shed skins, mud tubes, or bites with a specific pattern. When uncertain, a professional inspection is faster than months of misidentification.

Can I treat this myself or do I need a professional?

DIY is effective for small, accessible infestations caught early. Professionals are worth the cost when: the infestation is inside wall voids or structural elements, multiple rooms are affected, you have health-risk pests (hantavirus, venomous species), or DIY has already failed twice.

How long until the infestation is completely gone?

Expect 3–8 weeks for most infestations with proper treatment. Insects with dormant life stages (pupae, eggs) extend the timeline because those stages are impervious to most insecticides. Follow-up treatments at 2 and 4 weeks catch each new cohort as they emerge.

What's the most common mistake people make treating this pest?

Treating only the visible pest population while ignoring the harborage site, entry point, or breeding location. Killing adults provides temporary relief but the population rebuilds from hidden egg cases, pupae, or new arrivals through unaddressed entry points.

🐛 Bagworm