A Rose Slug by Any Other Name

By Gil Medeiros, Fairfax Master Gardener
“A rose is a rose is a rose,” wrote the poet Gertrude Stein 113 years ago. However, a rose slug is NOT a slug, and it is not even a caterpillar. It is technically a wasp. Confused yet? I will try to explain.

rose slug

Rose slug

The rose slug, bane of rose gardeners in this area, is actually the larval stage of the European Sawfly (Endelomyia aethiops, formerly Caliroa aethiops). It is in the order Hymenoptera with bees, wasps, and ants.

If you grow roses in Fairfax, you either have rose slugs or you soon will. And those “problem-free” Knock Out roses are just as susceptible to rose slugs as any other rose.

May is the month when Rose slugs first appear.

The damage appears as irregular translucent or tan spots on the leaves. This is because the young, 1/2 inch-long larvae eat only the top surface of the leaf. Their mouthparts are not large enough to chew through to the other side. Eventually the damaged areas die, and the spots becomes holes. Enough holes and spots produce a very tattered rosebush.

Fortunately for us, there is only one generation of the European Sawfly every year. But the news is not all good on this front because there is a second type of rose slug that shows up a little later in the season to finish off what’s left of the rose foliage. It is called the Bristly Rose Slug (Cladius difformis),the larvae of a different sawfly.