rose slug

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. The larva of either of two sawflies (Cladius isomerus or Endelomyia aethiops) that feeds destructively on the leaves of roses.

GNU Webster's 1913

1. n. (Zoöl.) the small green larva of a black sawfly (Selandria rosæ). These larvæ feed in groups on the parenchyma of the leaves of rosebushes, and are often abundant and very destructive.