The larvae of sawfly species, oak slugs, get their name from their resemblance to the legless molluscs, slugs, but are actually in the insect family Tenthredinidae in the order Hymenoptera which includes bees and wasps. Like similar species of sawflies on rose or pears, the larvae can be found skeletonizing leaf surfaces, usually feeding on the underside of leaves. Although the species in these images are yet to be confirmed, it is thought to be either Caliroa distincta or Caliroa labata, two species confirmed in Washington state.
Feeding damage from the larvae has been spotted in early July in the North Willamette Valley. Look on lower leaves for first damage as these sawflies generally overwinter in the soil below the trees.
At this time in Oregon, damage from oak slugs is minimal and primarily aesthetic, requiring no or limited intervention.
Web resources:
USDA-Forest Service, Northeastern Region. Scarlet Slug Oak Sawfly
University of Illinois Extension. Oak Sawfly
Original version: <3 August 2011)
Last update <24 July 2017>
Author: R.L. Rosetta, Extension Nursery Integrated Pest Management, Department of Horticulture, Oregon State University/NWREC.
Oak Slugs and Damage
Oak Slug Damage
Oak Slug Damage
Oak Slugs and Damage