Water Scorpion & Giant Water Bug

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PestControlBasics Editorial Team

Reviewed by Derek Giordano · Updated 2026

Illustrated identification guide — PestControlBasics.com

🔍 Identification

Water Scorpion (Nepa): 35-45mm; brown; flat and dead-leaf-shaped with long breathing tube at tail; two grasping front legs. Slow-moving; ambush predator.
Backswimmer (Notonecta): 10-15mm; boat-shaped; swims UPSIDE DOWN with long oar-like hind legs; can bite if handled.
Water Boatman: 5-12mm; swims right-side up; oar-like hind legs; generally harmless; often attracted to outdoor lights.

🧬 Biology & Behavior

All are aquatic predators (except water boatmen which eat algae). They breathe air, flying between water bodies at night. All can fly and are attracted to lights near water — this is how they end up in pools and occasionally indoors.

⚠️ Damage & Health Risk

No structural damage, no disease transmission. Backswimmer bites can be painful if the insect is handled — similar to a bee sting. Water scorpions can also bite defensively. Neither is medically significant.

🔧 DIY Treatment

For swimming pools: these insects fly in at night. Reduce poolside lighting or use yellow/sodium spectrum bulbs. Skim pools regularly. No pesticide treatment of pool water warranted or appropriate. If found indoors: capture in a jar and release near a water body.

👷 When to Call a Pro

Never warranted for occasional pool or indoor encounters with aquatic insects.

❓ FAQ

Do backswimmers bite?

Yes — backswimmers (Notonecta) can deliver a surprisingly painful defensive bite if handled. The bite is similar in intensity to a bee sting. They don't seek out people to bite and only bite when directly handled or trapped against skin.

Why are aquatic bugs in my pool?

They fly between water bodies at night and are attracted to the reflective surface of pools (which looks like a water body from above in moonlight) and to poolside lighting. They're typically found dead in the morning after swimming in chlorinated water.

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 🐛 Water Scorpion & Aquatic True Bugs

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.

🐛 Water Scorpion & Aquatic True Bugs