Field Identification
The larva of a sawfly—not a slug at all—that skeletonizes rose leaves from the underside, leaving upper epidermis intact like windowpane damage. Heavy feeding weakens repeat-blooming shrubs and makes ornamentals look moth-eaten. Adults are small wasp-like sawflies that insert eggs into leaf tissue. Common on garden roses across temperate North America and in similar climates in the Andes and upland Central America where roses are grown—roughly zones 4–9—with multiple generations where summers are long.
Larvae are yellow-green, translucent, and broad—slug-shaped with no obvious legs from above; head capsule and thoracic legs are visible underneath. Damage starts as pale patches that become lacy. Adults are shiny dark, about 1/4 inch (6 mm), and hard to spot—timing control to larval flushes is easier than adult hunting.
How to Deal With It
Organic Control Methods
Insecticidal soap or spinosad directed to leaf undersides kills small larvae on contact; repeat every few days while new hatch appears. Neem reduces feeding when coverage is thorough. Spray in evening to reduce UV breakdown and non-target pollinator overlap on blooming varieties.
Birds, paper wasps, and predatory beetles consume larvae; small parasitic wasps attack sawfly larvae in some regions. Mixed perennial borders with diverse bloom support generalist predators without monoculture rose hedges that amplify outbreaks.
Select rugosa and other leathery-leaf types where they fit the design—often tolerate light damage better. Avoid overhead irrigation schedules that keep undersides wet and soft for long periods. Prune out heavily skeletonized canes on hybrid teas to stimulate clean growth.
Rub larvae off by hand on small plantings—gloved thumb on the underside smears them quickly. Forceful water rinse from below dislodges early instars onto soil where ground predators finish the job.
Flip leaves weekly during peak summer—first spots appear on lower interior canopy. Flag cultivars that chronically flag for targeted early soap passes next year.
Let Nature Handle It
Natural Enemies
- Paper Wasps (Polistes spp.)
- Insectivorous Birds
- Ground Beetles (Carabidae)
- Parasitic Wasps (Hymenoptera)
Threat Map