By Linda Williams, forest health specialist, Woodruff, Linda.Williams@wisconsin.gov, 920-360-0665

Oaks in some northern counties are experiencing defoliation from oak sawflies this year. These native defoliating insects are small, hairless, semi-transparent larvae or “slugs” that feed on oak leaves.

Oak slug sawflies feed in groups on the undersides of oak leaves.

Oak slug sawflies can be found on the undersides of oak leaves feeding in small groups. They eat the material between the veins, leaving the upper epidermal layer intact and creating a “picture window” effect when you hold the leaves up to the light.

Close-up image highlights the semi-transparent and hairless larvae.

This insect is not considered a threat to oak trees or forests and populations are usually kept in check by natural enemies. If you want to control the pest using chemical means, make sure to use a general (not caterpillar-specific) insecticide since this is the larvae of a sawfly and not a caterpillar.