Imported Cabbageworm

🔬

PestControlBasics Editorial Team

Reviewed by Derek Giordano · Updated 2026

Illustrated identification guide — PestControlBasics.com

🔍 Identification

Adults: Small white butterfly with black wing spots — the 'cabbage white' common throughout North America. Larvae: 25-35mm; velvety green with a faint yellow stripe along the back; blend perfectly with green cabbage leaves; slow-moving. Eggs: tiny, bullet-shaped, pale yellow, laid singly on leaf undersides. Found on all brassicas: cabbage, broccoli, kale, Brussels sprouts, cauliflower.

🧬 Biology & Behavior

Multiple overlapping generations per year from spring to fall. Adults are excellent colonizers — a single female can lay 200+ eggs over her lifetime, one egg at a time. Larvae blend perfectly with cabbage leaves and are difficult to spot until damage is apparent. They feed primarily on leaf undersides and in the developing head.

⚠️ Damage & Health Risk

Holes in outer leaves; contamination of cabbage heads (larvae feed inside and deposit feces in the head — making the head inedible without extensive cleaning); complete plant defoliation in severe pressure.

🔧 DIY Treatment

Bt kurstaki spray — most effective organic treatment when caterpillars are small. Apply to leaf undersides every 5-7 days. Row covers from transplant prevent adult egg-laying entirely. Hand-pick larvae. Inspect cabbage heads before storage — squeeze gently to detect larvae inside.

👷 When to Call a Pro

Commercial brassica production uses threshold-based Bt programs timed to adult butterfly activity.

❓ FAQ

Is the white butterfly the pest?

The adult butterfly itself causes no plant damage — it only lays eggs. The caterpillar (larvae) is the damaging stage. The presence of white butterflies flying around brassicas is the egg-laying warning sign — apply Bt when you see the adults.

How do I get caterpillars out of cabbage heads?

Soak cut cabbage heads in salted water (2 tbsp per quart) for 30 minutes — caterpillars inside will emerge. Rinse thoroughly. This is the standard practice for harvested cabbage with suspected caterpillar contamination.

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 🐛 Imported Cabbageworm

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.

🐛 Imported Cabbageworm