Rose Slug

🐛 Rose Slug

Endelomyia aethiops / Cladius difformis · Hymenoptera: Tenthredinidae

Rose slugs look like caterpillars or tiny slugs but are actually sawfly larvae. They leave characteristic papery skeletonized windows on rose leaves. Bt does NOT work — they require spinosad.

Rose SlugSawflyTenthredinidaeSkeletonizingBt Does Not WorkRose

📐 FIELD GUIDE ILLUSTRATION

Slug and snail (Gastropoda) identification illustration with labeled anatomical features — PestControlBasics.com

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

🔬

PestControlBasics Editorial Team

Reviewed by Derek Giordano · Updated 2026

🔍 Identification

Larvae: 15-18mm; yellow-green; slimy appearance (resembles slug — the source of the misleading common name); found on leaf undersides, feeding on leaf tissue leaving papery upper epidermis intact. Damage: 'window paning' — transparent papery patches on leaves where lower tissue was eaten; turns brown and papery. Three species cause similar damage: bristly rose slug (Cladius), common rose slug (Endelomyia), and curled rose slug (Allantus).

🧬 Biology & Behavior

Rose slugs are sawfly larvae — sawflies are wasps (Hymenoptera), not flies. This matters for treatment: Bt kurstaki (effective on caterpillars) does NOT work on sawfly larvae. Spinosad IS effective. Adults lay eggs in leaf tissue in early spring. Multiple generations in some species. Peak damage in May-June and again in August-September for second generation.

⚠️ Damage & Health Risk

Extensive leaf skeletonization reducing photosynthesis; unsightly papery leaf damage reducing ornamental value; repeated defoliation weakening roses.

🔧 DIY Treatment

Spinosad spray applied to leaf undersides — the most effective treatment. Insecticidal soap as contact treatment. Water spray to dislodge larvae from undersides. Neem oil as repellent and contact treatment.

👷 When to Call a Pro

Rarely warranted for residential garden roses.

❓ FAQ

Why doesn't Bt work on rose slugs?

Rose slugs are sawfly larvae — the larvae of a wasp species, not a moth or butterfly. Bt kurstaki (Bt-k) is specifically toxic to caterpillars (Lepidoptera larvae) through a mechanism involving Lepidoptera-specific gut receptors. Sawfly larvae are Hymenoptera — different gut chemistry, different receptors. Bt-k has no effect on them. Use spinosad instead.

Are rose slugs related to garden slugs?

No — they're unrelated despite the name. Garden slugs are mollusks (related to snails). Rose slugs are insect larvae (sawfly larvae, which are related to bees and wasps). The 'slug' name comes from their slimy, slug-like appearance. Treatment for garden slugs (iron phosphate, beer traps) has no effect on rose slugs, and vice versa.

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 🐛 Rose Slug

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.