Pillbugs and Sowbugs

📐 FIELD GUIDE ILLUSTRATION

Millipede and pill bug identification illustration with labeled anatomical features — PestControlBasics.com

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

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PestControlBasics Editorial Team

Reviewed by Derek Giordano · Updated 2026

🔍 Identification

Pillbug: rolls into a perfect sphere — diagnostic. Grey, 10-15mm. Sowbug: cannot roll into ball; has two visible tail appendages; slightly flatter profile. Both: 7 pairs of legs; breathe through gills requiring moisture; found in mulch, under debris, and moist organic material.

🧬 Biology & Behavior

Both are beneficial decomposers improving soil health. Finding many indoors indicates entry point and excessive moisture near the foundation — they die within 24-48 hours indoors without moisture. Minor feeding on seedlings and strawberries reported but typically secondary feeding on already-damaged tissue.

⚠️ Damage & Health Risk

Nuisance indoor entry; minor seedling damage in very heavy populations; moisture problem indicator.

🔧 DIY Treatment

Fix moisture source — reduce mulch at foundation, improve drainage. Bifenthrin perimeter spray for immediate entry reduction.

👷 When to Call a Pro

Never warranted as primary treatment.

❓ FAQ

Are pillbugs harmful?

Completely harmless — no bite, sting, or disease transmission. Beneficial decomposers in gardens. The only concern is nuisance from entry into structures, which is a moisture management issue.

Why so many pillbugs in my basement?

Pillbugs breathe through gills and need moisture. A basement with large populations has chronically high humidity — dehumidifier plus drainage improvement typically resolves the issue.

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 🐛 Pillbug / Sowbug

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.

🐛 Pillbug / Sowbug